UC RIVERSIDE
ENTOMOLOGY

URBAN ENTOMOLOGY

by
Walter Ebeling

Chapter 7
Pests Of Stored Food Products

Summary | WHOLE Grain Pests | BROKEN Grain Pests | Legume Pests | Meats and Cheeses Pests | General Feeders
| Dried Fruit and Nuts Pests | Mite Pests | Figure Captions

Contents of Chapter

These pests cause losses to man by destroying large quantities of grain, corn, legumes (beans, lentils, peas), milled cereal products, flour, bran, macaroni and other paste products, pet foods, dried fruits, dried vegetables, cheese, nuts, candy, and other food materials. They contaminate, and thus eliminate for human consumption, far more food than they eat, and either cause directly or transmit diseases to man and his domestic animals (Scott, 1962-63). Although these marauders attain their greatest importance as pests of stored grain, damaging about 10% of the world's production, and as high as 30 to 40% in some tropical and subtropical countries (Munro, 1966), they are also important in the household as "pantry pests" that find their way into packaged cereals and other foodstuffs. Certain pantry pests may originate in crops when they are still growing in the field, while others may infest food products at any time until they are ready for use.

Pantry pests may fly into buildings from the outside, come from secluded harborages indoors, or migrate into uninfested items from infested ones or from refuse that has collected in cracks and crevices. They can also be carried into a building on materials other than food products. For example, drugstore and cigarette beetles, carpet beetles, spider beetles, psocids, and mites may gain entry via old furniture, rugs, drapes, bedding, or in or on almost any other product of plant or animal origin (Linsley and Michelbacher, 1943).

An idea of the species that can become pantry pests is obtained in surveys of grain elevators and feed mills. In one such survey made in Ohio, 34 species of beetles and moths were found. The granary weevil and the cadelle were the most important of the insects attacking sound, whole grain. The most important secondary invaders were the Mediterranean flour moth, flat grain beetle, sawtoothed grain beetle, mealworms, and 2 species of flour beetles (Triplehorn, 1965). In the southern states, the rice weevil is more important than the granary weevil or the cadelle, and world-wide it is considered to be "undoubtedly the most destructive insect pest of stored grain" (Cotton, 1963). However, as "pantry pests," the insects attacking sound, whole grain are relatively secondary in destructiveness. More harmful in this category are the species that attack broken grain or flour. Many kinds of insects have become adapted to feeding on stored flour, bran, and other processed grain products. In ancient times, only whole grain was stored, and there are many instances recorded of its having remained for remarkably long periods free of insect infestation (Hartnack, 1943).

Another factor affecting the infestation of stored grain or grain products is humidity, as it stimulates the growth of fungi. Sinha (1971) stated that insects that normally infested stored grain rarely occurred in the absence of fungi, and that several species were able to feed and survive on fungal diets.

Beginning in 1953, a summary was made of the results of extensive surveys by county, state, and federal inspectors of insects and mites associated with foods and seeds in storage throughout California. The specimens were identified by taxonomists of the State Bureau of Entomology (Strong and Okumura, 1958). Listed were 102 species of beetles, 27 moths, 1 psocid, 1 fly (cheese skipper), 3 Hymenoptera (the clover seed chalcid and 2 ants), 2 silverfish, 3 mites, and 9 species of natural enemies (parasites and predators) of stored-food pests. The beetles and moths comprised 87% of the arthropods found in the surveys. Beetles feed on stored products as both adults and larvae, but moths feed on them only as larvae. The great majority of pests of stored food products are beetles. A key has been prepared to help identify the species that are commonly encountered (Pratt and Scott, 1962).

Strong (1970) used a survey method that probably gave as good an idea of the relative abundance of pests that could invade the home pantry as it would be practicable to obtain on a large scale. In 30 localities, well distributed throughout California, he placed sheltered food packets in such places as carports, garages, equipment sheds, inactive dairy barns and poultry houses, old livestock barns, and other structures not being used to store dry food products, seeds, or feeds. The food packets consisted of 0.5 lb (0.23 kg) of a mixture of equal parts by weight of poultry laying mash, rolled barley, wheat, and corn, tied up in cheesecloth and covered with hardware cloth to keep out rodents. This is a mixture that would be expected to be a good food medium for insects that feed and develop on cracked grains or flour as well as those that feed and develop on whole. grains.

Table 6 lists the species, according to family, of the insects found infesting the food mixtures after ihey had been exposed in the 30 localities for 4 to 5 months during spring and summer, and also the number of areas in which each species was found. The list provides a good idea of the species that are potentially pantry pests in California, but not necessarily their relative importance, for it includes species that attack whole grains, which are seldom stored in home pantries. Nevertheless, the species one generally associates with the home pantry (cigarette beetle, drugstore beetle, sawtoothed grain beetle, confused flour beetle, red flour beetle, dermestids, ptinids, and the Mediterranean flour, Indian meal, almond, and tobacco moths) were well represented. The list includes only beetles and moths, but with the exception of the psocids (not included because they tended to escape in large numbers from.the food mixtures), other orders of insects were of no importance. The relative importance of some of the species might have been changed if dried fruits and nuts had been present along with the grains. Linsley (1942) pointed out that the majority of stored-product pests appeared to have evolved from insects infesting 1 or more of the following natural sources:

(1) Seed-infesting species which infest similar material in nature.

(2) Scavengers feeding generally on dead plant or animal products.

(3) Scavengers or semipredators living primarily under bark.

(4) Scavengers or predators inhabiting the nests of bees, wasps, or other aculeate Hymenoptera.

In the present chapter, the pests are divided into groups of similar habits with regard to the ways they affect stored food products; that is, whether they infest whole grain, broken grain, legumes, meats and cheeses, stored foods in general, or dried fruits and nuts. (Acarid mites are discussed separately.) This is followed by a section on the problems connected with insect contamination in milled cereal products. At the end of the chapter, certain control measures are discussed that may be employed while the food is still in the field, in storage, in the food-processing plant, and finally, in the home, where the offending insects and mites are generally called "pantry pests."

INSECTS INFESTING WHOLE GRAIN

Whole Grain Pests

Certain beetles and moths that primarily infest grain (wheat, oats, barley, rice, corn [maize], millet, and sorghum) have been placed in 2 groups, based on whether they feed on the whole grain or can feed on the grain only after it has been broken or ground into flour. Pests of whole grains will be discussed first. However, it should be borne in mind that stored whole grain ordinarily has enough broken kernels and grain dust to enable the second group to become established.

Granary Weevil, Sitophilus granarius (L.) (Curculionidae)

This is one of the most important and oldest known pests of stored grain. It is believed to have spread from its original home in the eastern Mediterranean area to the cooler regions of the entire world. In the United States, it is more frequently found in the northern states than in the South. It sometimes causes almost complete destruction of grain in grain elevators, farmers' bins, or ships. This species has become domesticated, and has lost its functional wings. It has forsaken both wild and cultivated field grains to infest only those in storage, and depends on man for dissemination. As a "pantry pest" in the home, it is not so important as some other beetles and moth larvae that are primarily pests of grains after they have been broken or milled. The adults have a tendency to wander about, and may first be seen by the housewife somewhat far from the infested materials.

Howe (1965) found that the granary weevil could infest acorns with cracked or removed shells, and preferred them to many common cereals. He suggested that the acorn might have been a host before the advent of primitive agriculture, especially when gathered by squirrels or man and kept in storage at moderate humidity. Another species of Sitophilus of larger size is a serious pest of acorns in India (Mathur, 1954). Sitophilus granariusmay also have been a larger insect before adapting itself to the infestation of stored grains. Likewise, the small strains of S. oryzae (described next) are believed to be adaptations toward a life in stored products (Kiritani, 1965).

Description. This polished chestnut-brown or blackish beetle (figure 177) is 9 to 4 mm long, and is similar in appearance to the closely related rice weevil, but lacks the pale markings of its elytra, and its vestigial wings are useless. The pits on the thorax are elongate rather than round or irreg.ularly shaped, as they are in the rice weevil. The small, legless larvae of the granary and rice weevils can be distinguished from those of other beetles infesting grain and other stored products by the ventral surface being straight (figure 177), while the dorsal surface is rounded. The larvae of the other beetles are more "wormlike" (figures 178 and 179). The larvae of any beetles can be distinguished from those of moths by not having the short, fleshy, leglike abdominal appendages known as "prolegs" (figures 180 and 185), that aid in locomotion and in clinging to surfaces.

Life Cycle. The female bores a hole in a grain kernel with the stout mandibles at the end of her long, slender snout, deposits an egg in the hole, and seals it with a gelatinous material. She may lay more than 200 eggs under favorable conditions. The eggs hatch in a few days, and the larvae feed on the interiors of the kernels, hollowing them out. There are 4 larval instars, and the developmental period is from 3 to 5 weeks. Pupation within the kernel requires 5 to 16 days. The entire life cycle may vary from as little as a month to as long as 5 months, depending on temperature. There are commonly 4 generations per year. The granary weevil is long-lived, surviving for 7 to 8 months as an adult. The female lays very few eggs at temperatures below 60 °F (16 °C), but can survive for 2 months or more at 35 °F (about 2 °C). A temperature of 120 °F (49 °C) for 1 hour or 130 °F (54 °C) for 0.5 hour is fatal.

Rice Weevil, Sitophilus oryzae (L.)

This insect is primarily a pest in warm countries, and in the United States it is most important in the South. The larva feeds inside a kernel of grain in which both larva and pupa must complete their development. Both larvae and adults eat similar food, but the latter can crawl or fly about and feed on various products. They have been reported to occur on beans, nuts, cereals wheat products, and grapes, and have been observed sucking the juice from apples and pears, gradually forming cavities in which they concealed themselves (Hinds and Turner, 1911). Unlike the granary weevil the adults have well developed wings, and fly from stored grain to fields of corn, wheat, or rice, and start infestations that continue in storage. In the northern states, infestation begins in new grain when it is stored in farm bins, warehouses, or grain elevators.

Description. The adult (plate IV, 5; figure 177, is 2.5 to 3.5 mm long, somewhat smaller than the granary weevil. It is reddish brown, with 4 faint reddish or yellowish spots on the elytra, round or irregularly shaped punctures on the pronotum, and with the head prolonged into a long, slender snout, bearing the mandibles at its tip.

Life Cycle. The female lives 4 to 5 months, and lays a total of 300 to 400 eggs. Like the granary weevil, she bores a small hole in the kernel with her mandibles, lays an egg in it, and covers the hole with a gelatinous fluid. The small, white, legless larva, with a brownish-black head, has 4 instars. In warm weather, the combined stages from egg to pupa may take as few as 26 days. After emergence, the adult stays in the kernel for 3 or 4 days, hardening and maturing, then bores its way out. This weevil is basically a grain pest, but has been reared from solidified farinaceous products stich as macaroni or caked flour (Cotton, 1963). The most favorable temperatures for development are 80 to 86 °F (27 to 30 °C). Below 45 °F (about 7 °C), the beetle is dormant. It usually dies after 2 weeks of freezing temperatures, or after an hour at 120 °F (49 °C).

Lesser Grain Borer, Rhyzopertha dominica (F.) (Bostrichidae)

This is one of the smallest of the grain-infesting beetles, but one of the most important. Originally native to the tropics, it has spread through commerce to all parts of the world. It is most prominent in the United States, southern Canada, Argentina, India, and Australia. In the United States, it is particularly widespread in the Gulf states. Both adults and larvae feed within the interiors of nearly all grains, including rice, and the kernels are reduced to mere shells.

Description. The adult (figure 178 and 179) is about 3 mm long, polished dark brown or black, and has a somewhat roughened surface. In common with other bostrichids, which are principally woodborers, Rhyzopertha dominica is almost cylindrical, and the head is vertically deflexed under the thorax so that it cannot be seen from above. Likewise, this insect, though small, has powerful jaws with which it can bore directly into wood (USDA, 1968). Wood may have been its original food. It can eat its way into wooden and paper boxes, and may destroy book bindings (Hoffman, 1933; Potter, 1935).

Life Cycle. The female lays 300 to 500 eggs, singly or in clusters, in the loose grain. They hatch in a few days. The larvae molt 2 to 4 times. They may feed on the flour produced by the boring of the adults, or may bore directly into kernels that have been slightly damaged. They complete their growth within the grain, transform to white pupae,.and the adults cut their way out (USDA, 1968). The life cycle takes only a month or two, depending on the temperature.

Other Bostrichids

Another bostrichid beetle that is believed to have acquired its grain-feeding habits relatively recently is the larger grain borer, Prostephanus truncatus (Horn). It is similar in appearance habits to the lesser grain borer, but is a little larger-about 4 mm long-and has a smooth polished surface. It is a tropical insect, not yet widely distributed in the United States, but can occasionally be found infesting corn in the southern states. It has also been reported from California, Texas, and the District of Columbia (USDA, 1968).

The bamboo borer, Dinoderus minutus (F.) (figure 133, chapter 5) is another bostrichid, and resembles Prostephanus truncatus in appearance, being cylindrical, brown, and 3 to 4 mm long. It infests bamboo, reducing the inner core to a fine powder. It has been recorded from many other hosts, including stored grain, but this is believed to be probably the result of misidentification (G.T.Okumura, personal communication).

Cadelle, Tenebroides mauritanicus (L.) (Ostomidae)

The cadelle is believed by some entomologists to be a native of America, for all species of the family Ostomidae are found in the New World. It is one of the best known of the stored-grain pests, in part because it is also a common "pantry pest" in the house, where adults and larvae feed on cereals, breakfast foods, potatoes, shelled and unshelled nuts, or fruit, and prefer to lay their eggs under the flaps of cartons. They can gnaw through sacks and paper packages. Unlike the granary and rice weevils, they feed not only on whole grains, but also on flour and a variety of other products, and are therefore much more important as pantry pests.

The cadelle may have been originally a predator under loose bark, as other species of the family are today. It does attack the larvae of other grain-infesting insects. Another peculiarity of this insect is its habit of burrowing into the woodwork of grain bins or other wooden structures, sometimes causing them to collapse. It may remain there for long periods in large numbers, only to emerge and infest the next load of grain. Other grain pests may also hide in its burrows.

Description. The shiny black adult (plate IV, 7) is elongate, oblong, and flattened, and is one of the largest of the grain-infesting beetles, being about 8 mm long. The prothorax, is distinctly separated from the rest of the body by a loose, prominent joint.

Life Cycle. The females lay about 1,000 eggs loosely in flour, grain, or other foodstuff. The fleshy, white to grayish-white larva has a black head and a black plate with two horny black projections at the tip of the abdomen. The life cycle may be as short as 70 days, but it may be much longer under conditions unfavorable to the insect's development. The females generally live for a year, and have been kept alive for more than 3 years.

Angoumois Grain Moth, Sitotroga cerealella (Olivier) (Gelechiidae)

The Angoumois grain moth is second only to the rice and granary weevils in its importance as a pest of stored grain in the United States. It attacks grains maturing in the field as well as in storage. Infested grain in storage has a sickening taste and smell that make it unpalatable. Only whole grain is attacked, so other grain products are safe (Linsley and Michelbacher, 1943).

Description. The adults (plate V, 2 and figure 180) are small, buff to grayish or yellowish-brown moths, with a wingspread of 13 to 17 mm. The size of the adult depends on how much food the larva has consumed. The hindwings narrow down to a point apically, and are heavily margined with long hairs.

Life Cycle. Each female lays an average of about 40 tiny white eggs on or near the grain, and in 4 to 8 days these hatch into minute, white larvae that bore into the kernels. The larvae are pale yellowish when mature, with a yellowish-brown head, and are about 5 mm long when full grown. They have poorly developed abdominal prolegs (figure 180, C). The larva passes through 3 instars in about 3 weeks, but may hibernate before changing to a reddish-brown pupa in the spring. Pupation takes place in a silken cocoon in the feeding cavity in the kernel. There are 2 to 4 generations a year.

European Grain Moth, Nemapogon granella (L.) (Tineidae)

This moth is creamy white, thickly mottled with brown. It is about the size of the Angoumois grain moth, but the mottled appearance distinguishes it from that species. The forewings are mottled with brown and white and the hindwings are gray, narrowed down at the apex like those of the Angoumois grain moth, and with long hairs along the edges. The larvae feed on all kinds of grain, in the field and in storage, and web the kernels together. This species is distributed throughout the northern states, but not abundantly, and is not so destructive as the Angoumois grain moth (USDA, 1968).

Pink Scavenger Caterpillar, Sathrobrota rileyi (Walsingham) ( = Pyroderces) (Cosmopterygidae)

This highly adaptable insect had for many years been known as a scavenger commonly found in cotton in North and South America, the West Indies, and Hawaii. It was necessary to be able to distinguish the small, reddish larvae from those of the pink bollworm, Pectinophora gossypiella (Saunders), and this led to the first complete description (Busck, 1917).

Description. The moth (figure 181) has a wingspread of 9 to 12 mm. The forewings are chestnut brown, with whitish or straw-colored streaks edged by irregular black scales. The hindwings are pale gray, and are edged with long fringes. The head is light chestnut brown, the abdomen reddish brown, and the legs light reddish. The full-grown larva (figure 181) is 7 to 8 mm long, the abdomen is deep wine red, the thoracic shield is broad and dark brown, and the head is light brown. The pupa is light yellowish brown, and has a smooth surface.

Economic Importance. This insect has been causing considerable injury to corn in the southern states, beginning in the field and continuing after the corn is placed in storage. The larvae feed on the seeds, husks, and cobs, producing a large amount of frass that is loosely webbed together and fills the interstices between kernels or the cavities of kernels that have been eaten out. Although capable of causing serious damage to corn in the field and in cribs on southern farms, the insect is seldom an important pest of commercial shipments. On orange trees, it is primarily a scavenger, but when it is abundant, some larvae may feed on oranges, and have sometimes caused severe damage in California and Florida (Ebeling, 1959).

Psocids (Psocoptera)

The psocids are discussed more fully in chapter 10 as one of the groups of insects that are attracted to the household by excessively damp conditions, and, particularly by the development of molds. The greatest economic losses from psocid infestations in stored products result from the contamination of processed foods, especially when they are stored for long periods under domestic conditions (Champ and Smithers, 1965). Moderately high humidity is required for the actual survival of psocids, but the development of molds is not necessary for it. Considerable damage can be done to stored grain, for example, by feeding injury to the kernels. A psocid can chew a small hole through the seed coat and completely devour the germ. Heavy populations can develop in stored wheat, particularly if it has 12.5% or more of moisture content and the ambient relative humidity is 65% or more (Watt, 1965).

Finlayson (1933) stored wheat in trays to propagate eggs of the Angoumois grain moth, Sitotroga cerealella. Temperature was between 75 and 85 °F (24 and 29 °C), and the relative humidity varied from 75 to 90%. He observed that within 5 months-from the day the first psocids (Liposcelis divinatorius) were seen, the 32 boxes in which the trays were stored were completely covered with the psocids; he estimated that there were 200 million of these insects present. After about a month of infestation, the Sitotroga population began to decline. The psocids seemed to show no preference between feeding on crushed wheat or Sitotrogaeggs.

The humidity of the air in a storage facility and the water content of the stored product that are required for heavy infestations of psocids are about the same as for heavy infestations of tyroglyphid (acarid) mites (Solomon, 1946, 1962; Knülle, 1963a, b; Cunnington, 1965).

INSECTS INFESTING BROKEN GRAIN

BROKEN Grain Pests

This group is made up of insects that are generaI feeders on stored food, attacking not only broken grains, flour, and cereals, but such products as dried meat, vegetables, fruit, milk, sugar, candy, tobacco, or drugs. Certain insects will be briefly mentioned that are minor pests of stored foods but are also pests in other ways, and are considered more fully in other chapters. The acarid mites can be important pests of some of these stored-food products, but they are considered separately near the end of this chapter.

Confused Flour Beetle, Tribolium confusum Jacquelin duVal, and Red Flour Beetle, T. castaneum (Herbst) (Tenebrionidae)

These 2 flour beetles, along with the sawtoothed grain beetles and Indian meal moths, are considered to be the most important pests of stored foods in grocery stores and in the home. Tribolium spp. are believed to have been semipredators originally, feeding on living and dead materials under bark. Tribolium indicum Blair continues to live only under bark, and T. audax Halstead is usually found under bark, but is occasionally taken in seeds and meal. Tribolium destructor (Uytenboogaart) has been recorded only from seeds and other stored products (Good,1936). Tribolium confusum and T. castaneum are now pests of stored grains and grain products, peas, beans, shelled nuts, dried fruits, spices, chocolate, drugs, snuff, cayenne pepper, herbarium and museum specimens, and many other items, but they are sometimes found under bark also. They are unable to feed on undamaged grain, but are serious pests in flour mills. In the United States, the confused flour beetle is the more abundant of the 2 species in the northern states, whereas in the South, the red flour beetle is more abundant. They are about equal in numbers in the intermediate regions.

Description. Tribolium confusum and T. castaneum (plate IV, 6) are small, reddish-brown beetles, about 3.5 mm long. They are similar in size and appearance as well as in life histories and habits. However, they can be distinguished with the aid of a hand lens. The antenna of T. confusum is gradually enlarged toward the tip, ending in "club" of 4 segments, whereas that of T. castaneum is abruptly clublike, with the club consisting of 3 segments. Tribolium confusum has the sides of the thorax almost straight, while those of T. castaneumare curved.

Life Cycle. Each female deposits 400 to 500 clear-white, sticky eggs on or among food particles, in cracks, or through the meshes of sacks containing. food, such as cereal products. She lays only 2 or 8 per day, but she is long-lived, and may survive as long as 2 years. The tiny eggs can be removed from flour by sifting it through bolting cloth. They hatch in 5 to 12 days into small, brownish-white larvae, which go through 5 to 12 instars, and reach maturity in as few as 30 days under optimum conditions, but may require up to 4 months. The full-grown larvae are 4 to 5 mm long, slender, cylindrical, wiry in appearance, and white, tinged yellowish. They can be distinguished from the larvae of other species that are somewhat similar in appearance by the prominent, 2-pointed termination of the last body segment.

As the larvae mature, they come to the surface of the food medium to transform into naked white pupae. In heated storehouses and mills, there are 4 or 5 generations annually. Good (1936) stated that the life cycle of T. confusum was 11 "somewhat longer" than that of T. castaneum, but that the optimum temperature appeared to be the same-30 °C (86 °F) for both species. The author has observed for years, when rearing the 2 species at ordinary room temperatures in a food medium of 47.5% white flour, 47.5% cornmeal, and 5% brewer's yeast, that the yield of T. castaneum was always several times greater than that of T. confusum in a given period. In an experiment that started with 100 adults of T. castaneum in a 1-gal (4-l) rearing jar and 100 adults of T. confusum in another jar, after 32 days there were 2,135 live adult T. castaneumcompared with 112 live adult T. confusum.

Flour Beetles as Laboratory Test Insects

Neither of the foregoing beetles can climb up the vertical surfaces of glass containers. Besides this, Tribolium confusum adults cannot fly, their wings being nonfunctional, while the T. castaneum adults can fly, but seldom do. These features, plus the fact that they can be easily reared in large numbers, make the 2 flour beetles popular test insects in entomological laboratories. If a blotter is placed in the rearing jar, particularly after the food medium is momentarily agitated, large numbers of the beetles will crawl onto it, and can then be brushed into a beaker to await transfer to insecticide residues and other media used in laboratory experiments.

Yellow Mealworm, Tenebrio molitor L., and Dark Mealworm, T. obscurus F.

These 2 species are similar in appearance, habits, and life histories. Their common names are based on the colors of the larvae infesting stored products. They are nocturnal, and seek moist, dark, undisturbed places. They may be found "in accumulations of grain in neglected corners of mills, under bags of feed in warehouses and feed stores, in grain bins where some of the grain has become damp, or in the litter of chickenhouses and birdhouses where feathers and refuse grain are mixed with excrement" (Cotton, 1963).

Mealworms are of only moderate importance as pantry pests. The larvae are probably best known as fish bait or as food for fish, amphibians, reptiles, birds, and small mammals kept as household pets or in zoos. They are reared commercially in enormous quantities for these purposes. They are also commonly reared by entomologists as test insects for evaluation of insecticides or for other experimental purposes. As a food medium, Cotton (1963) suggested wheat bran, to which would be added a little graham flour and commercial meal scrap, with an occasional addition of raw, fresh vegetables, such as carrots, potatoes, or lettuce. Commercial producers of mealworms utilize joints of the prickly-pear cactus instead of fresh vegetables.

Biology. The adult Tenebrio molitor is shiny dark brown to black, while T. obscurus is pitchblack (plate IV, 6). Both are more than 12 mm long. The female lays an average of 400 to 500 beanshaped, sticky, white eggs, to which particles of the food medium adhere. The eggs are laid singly or in clusters in the food material. In about 2 weeks, they hatch into slender, white larvae, which soon acquire the characteristic color of their species: bright yellow for the yellow mealworm and dark brown for the dark mealworm. The larvae have a hard, shiny cuticle that gives them a resemblance to the larvae of elaterid beetles (wireworms). After 14 or 15 molts, the larvae pupate near the surface of their food medium. The adults normally emerge in the spring and early summer, and live for 2 to 3 months, and there is 1 full generation per year (Cotton and St. George, 1929; Cotton, 1963).

Mealworms and Canthariasis. In cases of gastrointestinal canthariasis (infestation by beetle larvae), mealworms are the ones most often implicated. Eggs or larvae are ingested in cereals and breakfast foods, and in either case live larvae may eventually be passed in the feces (Palmer, 1946).

Related Species

The lesser mealworm, Alphitobius diaperinus (Panzer), is a black or very dark reddish-brown beetle, 5 to 6 mm long (figure 182). The larva is yellowish brown, and resembles the young larvae of the true mealworms. this species may become a pantry pest in damp situations. It feeds on such materials as damp and moldy grain, milled products, and spoiled foods (Cotton and Good, 1937).

The black fungus beetle, Alphitobius laevigatus (F.) resembles A. diaperinus in form and habits. It is shiny black above, reddish brown beneath, and the antennae and legs are brownish. The surface of the thorax is coarsely and profusely punctate, while that of A. diaperinus is finely and sparsely punctate. It is not so abundant as the lesser mealworm.

Other Tenebrionid Beetles

There are some related tenebrionids of minor importance. The black flour beetle, Tribolium audax Halstead, has long been known in the United States and Canada under the name T. madens (Charpentier), which is a European species not known to occur in North America. It is 2.8 to 4.5 mm long, and very dark brown. (The true T. madens is 3.8 to 5.1 mm long, among other characters.) Tribolium audax is most abundant in the Rocky Mountain areas of both the United States and Canada, but is also widely distributed elsewhere. It has occasionally been recorded from stored grain, meal, and flour, but is more often found outdoors under pine bark, in leaf mold, and inside beehives; the latter are common habitats for species of this genus. In Utah, large numbers were collected from the cells of the wild bee Megachile rotundata (F.), a highly successful pollinator of alfalfa (Halstead, 1969).

Another flour beetle, Tribolium incidens Charpentier, is usually found under the bark of trees, but occasionally in flour, meal, seeds, and grain. The false black flour beetle, T. destructor (Uytenboogaart), resembles T. confusum, but is slightly larger, and is black. In California, it is found in flour, grains, and mixed feeds (Strong and Okumura, 1958).

The longheaded flour beetle, Latheticus oryzae Waterhouse, is pale yellowish brown, slender, flattened, and less than 3 mm long. It resembles T. confusum in size and shape, but is lighter in color. It is widespread in the southern and midwestern states in rice and flour mills, causing the same type of damage as the confused flour beetle.

The broadhorned flour beetle, Gnathocerus cornutus (F.), derives its name from a pair of broad, stout horns on the mandibles. It is a stout, reddish-brown beetle, about 4 mm long. It is common in most of the United States except in the Great Plains area, where,it is comparatively rare. It feeds principally on flour and meal. The slenderhorned flour beetle, Gnathocerus maxillosus (F.), resembles G. cornutus, but is a little smaller, and the horns on the mandibles are slender and incurved. It is less common than G. cornutus, and occurs principally in the southern states (USDA, 1968).

Flat Grain Beetle, Cryptolestes pusillus (Schönherr) (Cucujidae)

This beetle is widely distributed, and is one of the most common pests of stored grain, but it cannot attack sound, uninjured kernels. The larvae also feed on dead insects, and often subsist as scavengers.

Description. The small, flattened, reddish brown adult (plate IV, 5; figure 183) is only about 2 mm long. The male's antennae are not quite as long as its body, and those of the female are about half as long. The elytra have 5 parallel ridges. The beetles can both jump and fly.

Life Cycle. The female oviposits in crevices in the grain, or in loose, farinaceous material. The larva is slender and pale, with a black head, and has a pair of slender, black, spinelike processes at its posterior end (Linsley and Michelbacher, 1943). It is particularly fond of the germ of the wheat, and many kernels are left uninjured except for the removal of the germ. The fullgrown larva forms a cocoon of a gelatinous substance to which food particles adhere. Development from egg to adult may require only 5 weeks under favorable conditions, although the average in summer is about 9 weeks. The adult female may live a year (Payne, 1946; Cotton, 1963).

Other Cucujids

Another species of Cryptolestes, C. turcicus (Grouvelle), resembles C. pusillus, but the male's antenna is as long as or longer than its body. The rusty grain beetle, C. ferrugineus (Stephens), is similar to C. pusillus in both appearance and habits, but the male's antennae are not more than half as long as the body. In the northern states and Canada, it is more commonly found in stored grain than the other 2 species (Cotton, 1963).

Siamese Grain Beetle, Lophocateres pusillus (Klug) (Trogositidae)

This cosmopolitan species attacks a wide variety of legumes, rice and rice products, other cereals, and various food products such as cocoa beans, coffee beans, cotton seeds, nutmeg, cassava, sweet potatoes, and dried fruits (Halstead, 1968). It is basically a tropical species, and is a relatively minor pest that is particularly associated with rice. Sound rice kernels are resistant to infestation, but they can be attacked if damaged (Corbett and Pagden, 1941).

Biology. The elongated, flat, reddish-brown female lays her eggs in crevices in fanshaped clusters of 11 to 14 eggs. They fail to hatch at temperatures below 15 or above 37 °C (59 or 99 °F), and the minimum incubation period is 5.8 days at 35 °C (95 °F). There are 4 larval instars. At 23 °C (73 °F) and 75% relative humidity, the larval stage requires an average of 53.8 days. The last instar larva makes a cell in the food preceding pupation. The mean duration of the total life cycle (oviposition to adult) at 95% relative humidity is 179.7 days at 20 °C (68 °F) and 48.8 days at 35 °C (95 °F) (Halstead, 1968).

Broadnosed Grain Weevil, Caulophilus oryzae (Gyllenhal) [=latinasus (Say)] (Curculionidae)

The adult beetle is about 3 mm long. It has the typical prolonged snout of the weevils, and resembles the rice weevil (Sitophilus oryzae), having pitted elytra, but is darker brown. It is widespread in the southern United States. Unlike the rice and granary weevils, this species cannot feed on whole grain or any seed that is dry and hard. It is often associated with the rice weevil, and feeds on grain that the latter has damaged. In California, it can often be found in an orchard in avocado seeds on the ground (figure 184). It bores through the rotting flesh of fallen avocados and enters the seeds. It has been known to infest avocado seeds that had been planted in nursery beds.

Life Cycle. The female lays between 200 and 300 eggs. In summer, the period from egg to adult is about a month, and the adults may live for another 5 months (Cotton, 1963).

Mediterranean Flour Moth, Anagasta kuehniella (Zeller) (= Ephestia) (Pyralidae)

The Mediterranean flour moth owes its name to the belief by some authorities that this insect, now world-wide in distribution, originated in the Mediterranean region. It first appeared in the United States in California in 1892. The larvae spin silken threads that cause a matting of flour particles that may clog machinery in flour mills. Modern fumigation methods have greatly decreased the importance of this pest in mills, but it is still one of the important pantry pests in the home.

The mature larvae crawl around extensively, and may be found anywhere in the house. This moth infests flour, cereals, bran, biscuits, dog food, nuts, seeds, chocolate, dried fruits, and many other stored foods.

Description. The adult moth (plate V, 1; figure 185) is 7 to 12 mm long, and has a wingspread of 24 mm or less. The forewings are pale gray, transversely marked with 2 zigzag black lines. The hindwings are dirty-white. When at rest, the forepart of the body is arched in a characteristic posture.

Life Cycle. The female lays several hundred eggs in flour or other larval food, and they hatch in 3 to 5 days. The larvae (figure 185) confine themselves in silken tubes, and, are full grown in 40 days, being about 15 mm long and whitish pink. They pupate in clean flour or other food material in silken cocoons or may not spin cocoons if they pupate in cracks or crevices. In any case, they leave the mass of infested material at this period. The pupal stage lasts 8 to 12 days, and the entire life cycle usually takes 9 to 10 weeks. The rate of development is largely determined by temperature. Under favorable conditions, there may be at least 4 or 5 generations in a year.

Indian Meal Moth, Plodia interpunctella (Hübner) (Pyralidae)

This cosmopolitan insect prefers the coarser grades of flour, and is therefore the most common pest in wholewheat or graham flour and cornmeal (Indian meal). The common name was given by Asa Fitch, an early American entomologist, who found the larvae feeding on cornmeal. It also breeds successfully in shelled or ear corn, matting it over with silken threads. In the home, it infests broken grain and grain products, dried fruits, seeds, crackers, biscuits, nuts, powdered milk, chocolate, candy, red peppers, and dog food. By its extensive webbing, it spoils more food than it can consume.

Description. The adult Indian meal moth (plate V, 1; figure 186) has a wingspread of about 20 mm. The wings are pale gray, and the outer portion of the forewing is reddish brown, with a coppery luster. The adults are often seen flying about in the home, and are likely to be mistaken for clothes moths, but the wing color is very distinct from the uniform gray of the clothes moth's wings.

Life Cycle. Although generations overlap as the season progresses, oviposition usually starts in April, the female layin 200 to 400 eggs, singly or in groups, on the larval food over a period of up to 18 days. Egg-laying usually takes place at night. Shortly after hatching, the dirty-white larvae secrete themselves in crevices in the food medium, and feed in or near a tunnel-like case of silk with frass incorporated into it. The larva (figure 186, B) generally retains its dirty-white color, but may be yellow, pink, brown, or greenish, depending on its food. The head and prothoracic shield are brown. The average length is about 13 mm when full grown. The larval period is considerably variable, depending on food and temperature. A heavy webbing usually extends throughout the infested material. The larvae crawl out of the infested food to spin their cocoons and pupate. In heavy infestations, they frequently pupate far away from the original food source. Complete life cycles have been noted to range from 27 to 305 days (Hamlin et al., 1931). There are generally 4 to 6 generations a year, but under favorable temperature conditions there may be 7 or 8.

The hymenopterous parasite Bracon hebetor Say is often seen in Indian meal moth infestations. According to Cotton (1963), outbreaks of the moth are nearly always terminated by this parasite, which can increase rapidly to enormous numbers.

Dermestid Beetles (Dermestidae)

The dermestid beetles are best known as scavengers and feeders on animal matter, but some species belonging to the genera Trogoderma, Attagenus, Anthrenus, and Dermestes can vary their diet by feeding at least in part on grain products. They are often found in warehouses, farm granaries, flour mills, and food-packaging plants, and particularly from the latter they may be transported to the home in infested food materials. They may also infest household food products after breeding in carpets, hides, bird or insect nests, dead rodents, or other sources of infestation within the house.

Trogoderma is the genus most commonly found in stored food, but not necessarily in the home. Some common species in the United States are T. variabile Ballion ( = parabile Beal), T. glabrum (Herbst) (plate IV, 4), T. inclusum LeConte, T. ornatum (Say), T. simplex Jayne, T. sternale Jayne, and T. grassmani Beal. Their relative abundance is greatly affected by climatic factors. In California, T. simplex was found to be the most widely distributed species among 18 climatic zones (Partida and Strong, 1970).

The khapra beetle, Trogoderma granarium Everts (plate IV, 3), is a serious pest of cereals in India and other parts of the world. Effective eradication measures have been taken whenever it has become established in the United States. According to Hinton (1945), it normally was found to feed on vegetable products, particularly wheat, barley, rice, and malt, and was the only dermestid for which he had found no recorded instances of feeding on materials of animal origin, although it would do so experimentally.

In the United States as a whole, the black carpet beetle, Attagenus megatoma (F.), is probably the dermestid pest most often encountered in the pantry feeding on farinaceous materials, but it is seldom found in California. The description and biology of this species are given in chapter 8. Other dermestids described in that chapter could also become pests of farinaceous food products. The dermestids that are principally attracted to cured meats are discussed under "Insects Infesting Meats and Cheeses" later in the present chapter.

Dermestids as Museum Pests

These beetles are notorious pests of dried plant and animal museum specimens. Dried insects are particularly susceptible to attack, and at least 22, species of dermestids have been recorded damaging insect collections in various parts of the world, apparently more than all other insect species combined. The 4 most important museum pests are: Anthrenus verbasci (L.), A. museorum (L.), A. scrophulariae (L.), and Trogoderma versicolor (Creutzer).

Allergy and Canthariasis

Dermestids can cause severe allergic reactions. A man doing research on the control of dermestid beetles and having "close contact" with the insects suffered severe reactions, including extreme difficulty in breathing. The condition became gradually worse over a 2-year period. Species principally involved were in the genus Trogoderma. A baby suffered digestive distress and pain (canthariasis) after eating cereal containing T. ornatum fragments. The irritation was caused by larval setae. Although approximately 90% of the Trogoderma, species received by the California Department of Agriculture are T. variabile, that species has not been recorded as causing canthariasis (Okumura, 1967).

After 3 years of rearing and otherwise working with carpet beetles (Anthrenus flavipes LeConte and Attagenus megatoma), a technician in our entomology laboratory began sneezing whenever he worked with the insects. After 10 years of such contacts with the beetles, he experienced severe itching and reddening of the eyeballs. The allergic reactions were apparently caused by dislodged hairs and fragments of cast skins.

Spider Beetles (Ptinidae)

Spider beetles are found throughout the world. They can remain active in freezing temperatures, and can therefore be pests in certain climates and circumstances in which other insects cannot. The farther north, the greater the relative importance of spider beetles. In North America, they attain their greatest relative importance in the northern U.S. and in Canada, where they can survive the winter in unheated warehouses and seriously infest cereal products during the spring and summer (Smallman, 1948). Because spider beetles can live as general scavengers, they can survive on rat droppings and miscellaneous debris in buildings such as empty warehouses. The source of infestation is sometimes difficult to locate.

Spider beetles tend to appear late in the succession of grain-infesting beetles. For example, in one investigation the succession of dominance of stored-grain beetles was found to be Sitophilus granarius, followed by Ptinus ocellus ( = tectus), and finally by the dermestid Attagenus pellio. Sitophilus granarius transformed whole wheat kernels into husks (empty grain) and frass (a fine powder, mostly feces), and then this species declined. The developmental rate of P. ocellus was most rapid on crushed, dead S. granarius, but was also faster on frass than on wholemeal flour (Coombs and Woodroffe, 1963, 1970).

In a large food-processing plant in Wisconsin, the principal breeding area for spider beetles was found to be the void of a dropped ceiling into which food particles sifted through cracks in the floor above. The silica aerogel Dri-die 67® was blown into the infested areas with a water-type fire-extinguisher (figure 33, chapter 3), eliminating them as sources of infestation by spider beetles and dermestids.

Biology. Spider beetles are small, 1.5 to 4.5 mm long, oval or cylindrical, and can be easily recognized by their long legs and the constriction of the prothorax near its base. As in the closely related family Anobiidae (see chapter 5), the prothorax extends over the head like a cowl. When the insect is viewed from above, the head is not visible, and only the long filiform or moniliform antennae can be seen. In figure 187, the specimens were drawn when tilted back at a 35° angle in order to make the heads visible. If they had been on a horizontal plane, the heads could not have been shown. Except for the antennae, these features combine to give the insects a fancied resemblance to small spiders, hence the common name.

The larvae are white, fleshy, and scarabaeiform (curved). There are usually 3 instars. They spin some silk, often in the form of a feeding cocoon. A cocoon is also spun in which to pupate, and the adult spends considerable time in it before emerging. According to König (1936), this cocoon is constructed from an anal secretion applied by the mouthparts, to which debris and particles of foodstuff adhere. Howe and Burges (1953) quoted Vajropala as stating that the silk of ptinids was secreted by the Malpighian tubules and mesenteron. The adult life is longer than the developmental period, and the female oviposits during most of it. However, few eggs are laid when larval food is unavailable, and readily obtainable drinking water is required to ensure maximum reproduction (Hickin, 1942; Ewer and Ewer, 1942; Howe and Burges, 1952).

Economic Importance. Most species of spider beetles are cosmopolitan, and are inclined to be omnivorous, feeding on broken grain or grain products, seeds, dried fruits or meats, wool, hair, feathers, rat and mouse droppings, insect and other animal remains, and plant and animal museum specimens. Howe (1959) pointed out that spider beetles had been observed in nature in dead or decaying wood, and that they also fed on mammal and bird dung. He made the interesting suggestion that some species were probably first introduced into primitive food-storage devices in the wood used to construct them. Some of the mammals and birds attracted to the food would have nested in the storage area, and their droppings would have provided "extra amenities" for spider beetles.

Spider beetles can be pests in warehouses, grain mills, museums, and homes, and appear to thrive best in old wooden buildings. In such structures, a typical scarring of the wood can sometimes be found where the insects have formed pupal cells. In California, one species (Ptinus ocellus) severely riddled the timbers of a grain elevator (Mackie, 1932). When preparing to pupate, this species also commonly damages containers made of cardboard, sacking, or wood. In warehouses, spider beetles are primarily pests of cereal products, particularly those that have long remained in storage. Their principal damage is the lowering of the quality of the stored food products because of the presence of dead insects and the silk and cocoons spun by the larvae. Whole grain is seldom seriously attacked, and any small damage that occurs is easily recognizable: the bran covering and the endosperm immediately beneath it are eaten off unevenly. The infestation is usually restricted to the peripheral few inches of a pile of stored grain (Howe and Burges, 1953).

One thing that increases the importance of spider beetles as warehouse pests is their habit of ovipositing through the meshes of cotton flour sacks. The adult beetles should be eliminated before they reach the sacks to oviposit (Gray, 1942; Smallman, 1948).

Principal Species

Included in the specimens identified by entomologists of the California State Bureau of Entomology from among the insects collected by county, state, and federal inspectors in a wide variety of foods and seeds in storage were 8 species of spider beetles. These, and the number of counties in which each species was collected, were as follows: Ptinus clavipes Panzer, 37; P. ocellus Brown, 18; P. fur (L.), 3; P. gandolphei Pic, 3; P. villiger (Reitter), 1; Gibbium psylloides (Czenpinski), 3; Mezium americanum (Laporte), 2; and Trigonogenius globulum Solier, 15 (Strong and Okumura, 1958). Among the species Strong (1970) collected in California in his mixed food baits, Ptinus clavipes was again the most abundant, but a few of the other species just named were not collected (table 6). However, 5 species not found in the 1958 survey were collected: Ptinus cognatus Fall, P. californicus Pic, P. verticalis LeConte, P. extendus Smith, and Niptus ventriculus LeConte.

These surveys may have indicated the relative importance of the various species as "pantry pests" in California, but their potentials for household damage might be different in other geographical areas. The least widely distributed species in California (P. villiger) is the most important one in Canada.

Australian Spider Beetle, Ptinus ocellus Brown (= tectus Boieldieu)

This is a cosmopolitan species, second only to P. clavipes in California in its importance as a pest (Strong and Okumura, 1958; Strong, 1970). Although it was not recorded in England until 1892, it has become one of the most widely distributed pests of stored food products in that country (Hickin, 1964).

Description. Ptinus ocellus (figure 187, A) is dull reddish brown, 3.5 to 4 mm long, with golden-brown or yellowish hair covering its elytra. This hair hides a series of longitudinal rows of small pits that are visible only when the hair is rubbed or worn off. This species can be confused with the male of P. fur.

Life Cycle. The female lays about 100 opalescent, sticky eggs, singly or in small groups, over a period of 3 to 4 weeks. Food and debris adhere to the eggs. The fleshy larva, covered with fine hairs, is strongly curved, and rolls up into a tight ball when disturbed. It can chew its way through sacking, cellophane, or cardboard, and can hollow out a chamber in adjacent woodwork when making a place in which to pupate. Pupation takes place in a tough, spherical, thin-walled cocoon. The adult may remain in this cocoon as long as 3 weeks after emergence (Hickin, 1964). Howe (1943) found that at 21 °C (70 °F) and 70% relative humidity, the eggs hatched in 8.6 days; the 3 larval instars required 59.9 days; the pupal stage, 15.9 days; the pre-emergence period (adult in cocoon), 9.5 days; and the total life cycle, from egg to the adult leaving the cocoon, 93.9 days.

Habits and Food Preferences. The adults are most active during darkness, emerging from their hiding places at dusk and returning at dawn. The hiding places are usually cracks and small crevices, and the larvae are inclined to pupate in them (Howe, 1950; Howe and Burges, 1953). This species can live and develop in accumulations of organic dust or in rodent droppings, and is often found in the nests of pigeons and other birds, even though it cannot fly (Howe and Burges, 1953). Large numbers of Ptinus ocellus were found in the nests of house sparrows in a warehouse, and the beetles were most numerous on or around the stacks of flour sacks nearest the nests (Cutler and Hosie, 1966).

The amazingly omnivorous nature of P. ocellus is typical of spider beetles in general, and is indicated by the following list of foods and other materials that it has been known to consume or bore into: almonds, beans, cacao, carpets, casein, cayenne pepper, chocolate powder, corn, crab meat, desiccated soup, dried fruits, dried insects, figs, fish food, fishmeal, furs (completely destroyed), ginger, lead cable, nutmegs, packaging materials, paprika, poultry food, raisins, rye, stored hops, and wood timbers. This beetle thrives best when the vitamin B content of its food is high, but can complete its development on materials of relatively low nutritive value, such as casein and pure starch. Its longevity and egglaying capacity are greatly increased if it has access to water at least once a week (Coombs and Woodroffe, 1965).

Brown Spider Beetle, Ptinus clavipes Panzer (=hirtellus) Sturm and brunneus Duftschmid)

Mallis (1969) stated that this insect was a scavenger in cellars, attics, storehouses, henhouses, and the like, and fed on "books, feathers, skins, dried mushrooms, the excrement of rats and other animals, the powdered leaves of such drugs as senna and jaborandi [Pilocarpus: Rutaceae], dried fruit, grains, and sugar." It was found to be more widely distributed and was taken from a greater variety of grains, legumes, various seeds, animal feeds, and mixed-food baits than any other spider beetle in California (Strong and Okumura, 1958; Strong, 1970).

Description. This beetle (figure 187, E, E) is uniformly pale brown in both sexes, as a rule, but may vary from dark brown in the male to blackish brown in the female; it ranges from 2.3 to 3.2 mm in length.

Life Cycle. Howe (1956a) gave the following data: The eggs hatched in 13 days at 22.5 °C (about 72 °F) and 70% relative humidity. The complete life cycle required 6 to 9 months. However, about one-third of the larvae entered diapause (see chapter 4), and remained larvae more than 10 months. Ptinus clavipes was able to complete a generation in 5 months at temperatures in which P. ocellus could not have survived.

Hairy Spider Beetle, Ptinus villiger (Reitter)

Smallman (1948) stated that this species was the spider beetle most commonly found in grain warehouses in Canada, with P. fur and P. raptor also occurring.

Description. The adult beetles (figure 187, D) are reddish brown. The elytra of both males and females have irregular white patches anteriorly and posteriorly, and those of the females also have several longitudinal rows of shallow pits. The length varies from 2.2 to 4 mm.

Life Cycle. The female may lay up to 40 pearly, spindleshaped eggs, 0.6 mm long. They are usually laid on the outsides of bags, through the meshes of sacks, and in flour debris in cracks and corners. They hatch into cream-colored larvae with brown head capsules, that complete their development in 3 months in warm weather, and become about 4 mm long when full grown. Pupation takes place in a silken cell coated with food material. The larva often overwinters in this pupal cell, and does not pupate until the following spring (Gray, 1934).

Whitemarked Spider Beetle, Ptinus fur (L.)

Description. The beetles are reddish brown, 2 to 4.3 mm long, and are covered with yellow hairs. The females (figure 187, C) are larger and more nearly globular than the males (figure 187, B), and unlike them, have 2 white patches anteriorly and posteriorly on each elytron. In some specimens, the patches are joined to form white stripes. This species closely resembles P. villiger in appearance and habits.

Life Cycle. The larvae, which superficially resemble those of the drugstore beetle (Stegobium paniceum), feed in a globular cell formed from their foodstuff. The complete life cycle varies from 1 to 3.5 months, depending on temperature and other factors.

Golden Spider Beetle, Niptus hololeucus (Faldermann)

In addition to the usual wide variety of products that are generally attacked by spider beetles, the adults and larvae of this species feed on woolens, linens, and natural silks, particularly if the fabrics are soiled with grease. The beetles are most commonly found in vegetable and animal debris in warehouses, poorly kept storerooms, cellars, and old houses, and sometimes occur in considerable numbers. They shun light, but move actively in the dark (Hickin, 1964). The nests of bees, wasps, and birds provide their natural habitats (Howe and Burges, 1952).

Description. The adults are 3 to 4.5 mm long and golden yellow, with long, silky hairs covering the fused elytra. Flight wings are absent.

Life Cycle. Oviposition and the appearance of the eggs and larvae are similar to their equivalents in Ptinus ocellus. The eggs hatch in 11 to 20 days at 64 to 68° F (18 to 20°C); the larval period lasts about 150 days; and the pupal period, 18 to 26 days. The adults may live as long as 250 days (Hickin, 1964).

American Spider Beetle, Mezium americanum (Laporte)

This species has been noted to occur in dwellings, warehouses, and mills in California, and has been taken from such materials as dried animal products, melon seeds, mixed feed, and woolen carpet (Strong and Okumura, 1958), and in grain, tobacco, cayenne pepper, and opium (Papp and Okumura, 1959). In a San Francisco residence, a continual renewal of infestation after treatment led to the discovery that spider beetles of this species were coming from an old rat nest under the bathroom. The nest contained dead rats, rat droppings, old bones, and other materials on which the insects could subsist. The otherwise inaccessible area could be reached with an insecticide dust, and control was obtained (Montgomery, 1936).

Description. Mezium americanum has a particularly striking appearance. It is 1.5 to 3.5 mm long, broadly oval, and the elytra are strongly convex (figure 187, I). It is shining dark reddish brown to nearly black. The "humped" elytra give this, as well as the following species, a conspicuous structural feature for easy identification.

Shiny Spider Beetle, Gibbium psylloides (Czenpinski)

This is a cosmopolitan species that is well established in California and other western states, where it has been recorded as feeding on woolens and various dried animal products.

Description. The shiny spider beetle (plate IV, 5; figure 187, G) is red to nearly black, with dense, short, yellow hairs beneath, and is 1.7 to 3.2 mm long. It closely resembles Mezium americanum in appearance and habits, but the head and thorax are entirely bare, while in M. americanum they are densely covered with small scales and scalelike hairs. Both species are striking in their "humped" appearance, and are easily distinguished from other spider beetles.

Life Cycle. Relatively few eggs are laid when compared with some species, such as Ptinus ocellus. The immature stages are similar in appearance to those of P. ocellus. The larvae do not wander away from the foodstuff for pupation, which takes place in a spherical cocoon. Gibbium psylloides appears to thrive under drier conditions than other spider beetles. The life cycle requires 22 to 42 weeks, and the adult usually lives another 30 to 40 weeks, but an adult life of 18.5 months at 25 °C (77 °F) has been recorded (Hickin, 1964).

Economic Importance. This beetle has been found in houses, hotels, warehouses, mills, granaries, bakeries, and latrines, and on sponge-rubber bath mats, woolens, and towels. It is recorded as feeding on cereals, wheat, bran, baby food, stored seeds, stale bread, dog biscuits, decaying animal and vegetable refuse, cayenne pepper, and opium cake (Hinton, 1940; Curran, 1946a). In England, it has long been known to occur in large numbers in old houses, damaging woolens and paper. It infests tallow, and has the ability to thrive on drugs, including opium (Hickin, 1964).

Globular Spider Beetle, Trigonogenius globulum Solier

Essig (1926) recorded this species from dried animal products, herbarium and insect specimens, seeds, red pepper, and cereals. He kept a living colony in a jar of manure for 8 years. Papp and Okumura (1959) recorded the beetle as breeding in large numbers in a manure pile and being found in burlap sacks and old clothing, as well as in grains and feeds.

Description. This spider beetle (figure 187, H) is 2.5 mm long, with both prothorax and abdomen nearly globular, the latter being twice as wide as the former. The adult is pale or dark brown, and is densely clothed above and beneath with pale yellowish-brown scales that are irregularly dispersed with darker brown on the elytra, atid with a small, elongate, blackish-brown spot on each side of the suture at the base of the elytra. There are no scales on the prothorax, but it bears a dense mat of interlacing hairs.

INSECTS INFESTING LEGUMES

Legume Pests

Bean Weevil, Acanthoscelides obtectus (Say) (Bruchidae)

This beetle, thought to be indigenous to North America, is the principal pest of stored legumes (kidney beans, peas, lentils) and certain other seeds, attacking them both in the field and in storage if they are stored in a warm place. If the field-infested material is brought into storage, the insects can reinfest the dried seeds. The bean weevil can be eliminated by destroying infested legumes because it does not attack grains, cereals, or other stored food products.

Description. Despite its name, this pest is not a true weevil; its head is not prolonged into a beak (plate IV, 8; figure 188). The adults are 2 to 3 mm long, robust, somewhat triangular (cut off squarely at the rear and narrowing toward the front), almost flat above, and are velvety gray or brown, with pale, linear markings on the elytra, which do not cover the tip of the abdomen. The thorax is covered with fine, yellowish-orange hairs, the legs are reddish yellow, and the antennae have serrate (sawtoothlike) segments.

Life Cycle. The female lays an average of 75 eggs, singly, on or near the beans or related seeds. The eggs hatch in 5 to 20 days, and the tiny, legless larvae proceed to bore into the seed; several larvae can develop in a single bean. The life cycle requires 21 to 80 days, and the newly emerged adult makes an exit hole and leaves the seed. The adults do not eat legume seeds. They fly actively during the day at 70 °F or more.

Cowpea Weevil, Callosobruchus maculatus (F.)

This insect is similar in size and habits to the bean weevil, but infests only cowpeas. The elytra are reddish brown, and each has 2 large, red spots. The thorax is covered with fine, white hairs. Whereas in the bean weevil the basal segment and the last segment of the antenna are reddish yellow, in the cowpea weevil only the basal segments are that color and the remainder of the antenna is dark.

Pea Weevil, Bruchus pisorum (L.)

Pea weevils are 4 to 5 mm long, gray to brownish gray, with small, distinct, white spots on the elytra. They attack peas in the field - one beetle per pea. The females must lay their eggs on the pods of growing pea plants in the spring or perish without ovipositing. Infested peas may be brought into storage, but eggs are never laid on dried peas, and there is no reinfestation in storage. Therefore, it is a relatively unimportant pantry pest compared with the bean weevil.

Broadbean Weevil, Bruchus rufimanus Boheman

This weevil is a pest only in California. It is only about two-thirds as large as the pea weevil, but is otherwise almost identical in appearance and habits. It prefers broad "beans" (Vicia faba), but also attacks other peas and vetches. Several weevils may be found in a single seed.

INSECTS INFESTING MEATS AND CHEESES

Meats and Cheeses Species list

Redlegged Ham Beetle, Necrobia rufipes (De Geer) (Cleridae)

This beetle is the most important of the insects that infest dried or smoked meats. It can be a serious pest where smoked meats are stored for long periods, and is the principal reason for the wrappings, sacks, and washes used for their protection. The larvae boring into the meat, particularly the fat parts, do most of the damage; the adults are surface feeders. The redlegged ham beetle has also been recorded attacking cheese, bones, hides, drying carrion, copra, salt fish, herring, dried egg yolks, dried figs, "guano", bone meal, palm-nut kernels, and Egyptian mummies. Substances infested but not fed upon have been silk, baled cotton, and woolen goods. These beetles belong to a family that is principally known as predaceous, and it is not surprising that they feed on the larvae of blow flies and cheese skippers that infest meat. When redlegged ham beetles become very numerous, their numbers are reduced by cannibalism (Simmons and Ellington, 1925). Infestation has been prevented by installing tightfitting doors and careful screening with fine (30mesh) wire cloth.

Description. The adult beetle (plate IV, 3; figure 189) is shiny green or greenish blue, with legs and bases of the antennae reddish brown, and is 3.5 to 7 mm long. It is convex, straightsided, and noticeably "punctured."

Life Cycle. The smooth, shiny, translucent eggs, 1 mm long, are glued in place, usually in clusters, on the surface of the foodstuff; during the adult life of 14 months or more, as many as 2,100 eggs may be laid. They hatch in 4 or 5 days in warm weather. The full-grown larvae are about 10 mm long, slender, tapering toward the head, and are purplish in color. They are repelled by light. There are 3 or 4 larval instars. The larva uses a frothy oral secretion for the construction of a white cocoon for pupation. The life cycle varies from 36 to 150 days or more, depending on the type of food and the temperature (Simmons and Ellington, 1925).

Related Species Two other species of Necrobia with habits similar to those of N. rufipes, but seldom recorded as pests are the redshouldered ham beetle. N. ruficollis (F.), and N. violacea (L.) (figure 189). Necrobia ruficollis is 6.2 mm long. The front of the head and the apical three-fourths of the elytra are metallic blue; the ventral surface of the head, the prothorax, the bases of the elytra, the meso and metasternum, and the legs are brownish red; and the antennae and abdomen are dark brown. Necrobia violacea is 4.5 mm long, and metallic dark blue or dark green, with very dark brown or entirely black antennae and legs. Both these species are cosmopolitan, and are commonly found on the skin and bones of dead animals and on dead fish. Necrobia violacea has been mentioned as a predator of Dermestes larvae, and may be more beneficial than harmful (Papp, 1959).

Larder Beetle, Dermestes lardarius L. (Dermestidae)

Refrigeration, the purchase of meat in small quantities, and almost complete discontinuance of the home curing of meat have resulted in the larder beetle becoming less important as a pest in modern times. It is now more likely to be introduced into the home with dog and cat food (Gray, 1947).

Description. This dark-brown beetle is about 8 mm long. On the basal third of each elytron there is a wide, yellow band with 3 black spots. The ventral surface of the body and the legs are covered with fine, yellow hairs, and the antennae are distinctly clubbed. The larva is brown and very hairy, as is typical of dermestids, and is 11 to 13 mm long. There are 2 curved dorsal spines (urogomphi) on the next-to-last abdominal segment.

Life Cycle. The adults overwinter in crevices of bark, and enter buildings in spring and early summer. They seek food such as ham, bacon, dried beef, dried fish, cheese, feathers, horn, skins, or hair on which to oviposit, but will lay eggs in cracks and crevices if no food is available. The female lays 100 or more eggs, and they hatch in 12 days or less. The larvae may burrow into ham, bacon, or anything available in the vicinity, such as wood or even lead. The male larvae molt 5 times and the females, 6, before seeking places in which to pupate. There is usually a single generation per year, but as many as 5 or 6 have been observed (Kreyenberg, 1928; Hinton, 1945).

Black Larder Beetle, Dermestes ater De Geer (=cadaverinus F.)

This species, in common with Dermestes lardarius, is an occasional pest of cured meats, cheese, and other foods of animal origin, and is sometimes found in packaged pet foods. Johnson (1945) stated that this species was commonly found in incinerators in Connecticut. In one apartment building, for example, it was found flying about, apparently having bred in dead mice in the building. The adults were often observed coming out of crevices and from behind baseboards and moldings. They appeared to have dispersed via wall voids from the incinerator room in the basement. Complete combustion of all waste material in the incinerators was recommended because odors from unburned garbage attracted the adult beetles. It was also suggested that all ashes and unburned material be removed every 2 weeks.

Biology. Dermestes ater is a black beetle, about the size and shape of D. lardarius, and with a yellowish-gray pubescence. It can be easily distinguished from D. lardarius because it lacks the dull-yellow band across the base of the elytra of the latter. The female may lay up to 400 eggs over a period of about 2 months. At 80 to 82 °F (27 to 28 °C), the period from egg to adult requires 6 weeks (Roth and Willis, 1950).

Hide Beetle, Dermestes maculatus De Geer (= vulpinus F.)

The hide beetle prefers to feed on hides and skins, and is less likely than the larder beetle to be a pest of stored food products. This species can damage such hard substances as hair brushes, cork, tea chests, and woodwork, which the mature larvae bore into in order to pupate. Severe damage to rafters of Douglas fir (Oregon pine) was caused by D. maculatus in a mill in which bones and offal were received (Brimblecombe, 1938).

Description. This species (plate IV, 3) is similar to the larder beetle in size, shape, and habits. It may be distinguished from that species by the fact that the elytra are uniformly dark and the undersurface is white. Each elytron terminates in a sharp point where the elytra join. The apical margins of the elytra are serrate.

Life Cycle. In one investigation, it was noted that the female oviposited in any available crack or crevice, and that the eggs hatched in 3 days. After 6 molts, the larvae sought places to pupate, boring into any available material. The pupal period lasted 10 to 11 days. The life cycle required 64 days (Illingworth, 1918).

Dermestes frischii Kugelann

Description. This species is similar to Dermestes maculatus in appearance and feeding habits but may be distinguished by the fact that the apical margins of the elytra are not serrate.

Life Cycle. Amos (1968) determined that the eggs hatched in periods ranging from 2 to 3 days up to 11 to 15 days in temperatures ranging from 40 to 15 °C (104 to 59 °F). The average number of eggs laid was 215. The larval stage lasted from a mean of 19.6 days at 35 °C (95 °F) and 90% relative humidity to 170.5 days at 20 °C (68 °F) and 45% RH. The investigation demonstrated the striking effect that humidity may have on the developmental periods of some insects. With this species, variation in relative humidity had about as great an effect as variation in temperature. Thus, at 25 °C (77 °F), the larval period averaged 40.5 days at 90%, 54.9 days at 75%, 74.6 days at 60%, 86.3 days at 45%, and 130.8 days at 30% RH. About the same range in the duration of the mean larval period was found at different temperatures at a constant RH of 60%: 35 days at 35 °C, 33.7 days at 30 °C, 74.6 days at 25 °C, and 132.8 days at 20 °C (95, 86, 77, and 68 °F).

Of equal interest in Amos' investigation was the finding that the presence of salt in fishmeal increased the developmental period and reduced the oviposition and rate of increase of Dermestes frischii. His data supported earlier field observations on the value of thorough salting and drying of fish for the control of this pest.

Cheese Skipper, Piophila casei (L.) (Diptera: Piophilidae)

The pests already described that infest meats and cheeses have all been beetles. There is also a fly of considerable importance - the cheese skipper. It occurs throughout the United States and most of the world. It is an important pest of cheese, but can also be destructive to cured pork. Other materials reported as foods of the cheese skipper include salted beef, smoked fish, brinecured fish, bones, animal carcasses, human cadavers, and various other materials consisting largely of animal proteins. When they are accidentally eaten with infested cheese or other cold, infested food, live maggots can pass into the intestines, where they may cause irritation, lesions, and diseases. Unspoiled, salvaged meat can be eaten safely if it is thoroughly cooked (Fulton, 1953).

Description. The adult (figure 190) is a small, black or bluish-black fly, with bronze tints on the thorax, yellow face, mouthparts, and antennae, reddish-brown eyes, and iridescent wings that lie flat over the body when at rest.

Life Cycle. The female lays an average of about 130 eggs on the surface of the food substance. The maggot travels by peristaltic movements of its body or, when full grown, by "skipping," a movement by which it can propel itself as much as 25 cm horizontally or 15 cm vertically. It bores into cheese or meat for the most part. When about to pupate, the larva (figure 190) migrates to some dark, dry crevice. The life cycle may occupy as little as 12 days. The adults feed on the juices of the larval food, but live only 3 or 4 days, and appear only in the warm season (Simmons, 1927).

Control methods for the cheese skipper are given under "Control of Pantry Pests" at the end of this chapter.

GENERAL FEEDERS ON STORED FOODS

General Feeders

Sawtoothed Grain BeetIe, Oryzaephilus surinamensis (L.) (Cucujidae)

This beetle often does considerable damage to grains, although its attack generally follows that of other insects, such as the granary or rice weevils; it cannot attack sound kernels. Its flat form allows it to penetrate into very narrow cracks, crevices, and imperfectly sealed packages. It is almost omnivorous, and attacks such foods as cereals, bread, macaroni, dried fruits, nuts, dried meats, sugar, and many other products. It is one of the most common pantry pests.

Description. The adult (plate IV, 5; figure 191) is a small, slender, flattened, brown beetle, about 3 mm long. It can be easily identified by the 6 sawlike "teeth" on each side of the thorax. The posterior femora of the males are armed with a tooth, while those of the females are not.

Life Cycle. The female lays 45 to 285 white, shiny eggs over a period of 2 to 5 months. They are deposited singly or in clusters in crevices in the foodstuff. In warm summer weather, at 80 to 85 °F (27 to 30 °C), they hatch in 3 to 5 days, and in cool spring and fall weather, at 68 to 73 °F (20 to 23 °C), in 8 to 17 days. The larvae molt 2 to 4 times (usually 3). When mature, they are yellowish white, and less than 3 mm long. Before pupation, they generally construct crude pupal cells or cocoons from particles of seeds or other foodstuffs, fastening them together with an oral secretion. Whether this cell is made or not, the larva attaches itself by its anal end to some solid object to pupate. The complete life cycle (egg to egg) may range from 27 to 375 days. The adult life may vary from a few days to more than 3 years (Back and Cotton, 1926). The adults have apparently never been seen in flight, although they have sometimes been captured in flight traps (Mallis, 1969).

Merchant Grain Beetle, Oryzaephilus mercator (Fauvel)

This species closely resembles Oryzaephilus surinamensis, and for many years the two were considered to be synonymous. Eventually, crossbreeding experiments proved that they were distinct species (Howe, 1956b). Also, a morphological difference can be seen with the aid of a hand lens. In O. mercator, the length of the temple (the region directly behind the eye) is less than half the vertical diameter of the eye, while in O. surinamensis, it is greater than half that dimension (figure 192) (Howe, 1956b; Hinton and Corbet, 1963). An extensive survey made in Canada in 1966 revealed that O. mercator was widely distributed in that country, but mostly in recessed cereals (rolled oats, rice, flour, cake mixes, macaroni, and cookies). In addition, it was found infesting nuts, coconut, and candy bars made with peanuts and puffed rice. It was found most frequently in kitchens in both apartment buildings and private residences. In imported commodities, those most often infested were copra, peanuts, and cashews from Asian countries, confirming Howe's belief that O. mercator was chiefly associated with oilbearing-seeds. This species has not been recorded in Canada from grain stored in either farm granaries or grain elevators. On the other hand, Oryzaephilus surinamensis is a pest of both stored grain and processed cereal products. It can apparently endure the low Canadian temperatures in unheated granaries, whereas O. mercator cannot (Loschiavo and Smith, 1970).

Cigarette Beetle, Lasioderma serricorne (F.) (Anobiidae)

This beetle is considered to be the most destructive pest found in stored tobacco, but it also has the reputation of attacking a wider range of foods than any other storage pest. It can live and fly outdoors in the tropics and subtropics, but can survive only in warm buildings in temperate regions. It is distributed throughout the United States and southern Canada.

Description. The adult beetle (plate IV, 7; figure 193) is light brown, small, oval, and about 3 mm long. In common with other anobiids, the ptinids, and the bostrichids, the head and prothorax are bent downward so as to give the insect a strongly humped appearance. It has occasionally been confused with the drugstore beetle (Stegobium paniceum), but L. serricorne has serrate antennae and smooth elytra, whereas in S. paniceum the last 3 antennal segments are long and broad, forming a distinct "club" and the elytra are striate. The larvae of the two species are also similar (plate IV, 7), except that the larva of L. serricorne has more and longer hairs, giving it a more fuzzy appearance.

Life Cycle. The female lays her oval, whitish eggs in and about the food materials, and they hatch in 6 to 10 days in warm weather. There are 4 to 6 larval instars. The full-grown larvae are about 4 mm long, curved, hairy, and pupate in silken cocoons covered with bits of foodstuffs. The life cycle may require 40 to 50 days, and there are usually 3 to 6 generations per year. The developmental period is affected by both humidity and temperature. Howe (1957) determined that at 30 °C (86 °F), the period required for the complete life cycle varied from a mean of 33.9 days at 70% relative humidity to 78.8 days at 40%, and that natural mortality increased from 50 to 73%, respectively. At 30% RH, there was 100% mortality. The minimal temperature for development was about 18 °C (65 °F), and food stored below that temperature was found to be safe from infestation. Swingle (1938) found that all stages of the beetle were killed at 36 °F (2.2 °C) for 16 days and 25 °F (-3.8 °C) for 7 days.

Food and Other Materials Attacked. Based on the records of many investigators, plant materials attacked by the cigarette beetle include: aniseed, areca nuts, atta (a wheat product in India), bamboo, beans, biscuits, cassava, chickpeas, cigars (figure 194), cigarettes, cocoa beans, coffee beans, copra, coriander, cottonseed (before and after harvest), cottonseed meal, cumin, dates, dried banana, dried cabbage, dried carrot, dried fruits, drugs, flax tow, flour, ginger, grain, herbs, herbarium specimens, insecticides containing pyrethrum, juniper seed, licorice root, paprika, peanuts, rhubarb, rice, seeds of various trees and plants, spices, and yeast (figure 194). It also breeds in animal matter, such as dried insects and dried fish, fishmeal, and meatmeal, and has been recorded attacking leather and the stored wax of Cocos coronata. This insect also feeds on furniture stuffing and bookbinders' paste, and may incidentally damage cloth, upholstery, paper, and books (Howe, 1957). Paprika and dog food are commonly infested in the home.

Drugstore Beetle, Stegobium paniceum (L.) (Anobiidae)

This cosmopolitan species resembles the cigarette beetle, and rivals it as a pantry pest. It feeds on any of the household foods and spices, as well as wool, hair, leather, horn, museum specimens, and drugs. It has been known to perforate books and wooden objects, and even tin or aluminum foil and lead.

Description. The adult is cylindrical, and 2.25 to 3.5 mm long (plate IV, 7; figures 193 and 179 [larval). The color is uniformly reddish to reddish brown. Very fine hairs are -arranged in longitudinal rows on the elytra. The drugstore beetle can be distinguished from the cigarette beetle by the distinctly striate elytra, the 3 enlarged segments at the tips of the antennae, and by the less hairy larva. When comparing the 2 species in figure 193, note that the sides of the pronotum of the cigarette beetle are more uniformly rounded than those of the drugstore beetle. The drugstore beetle resembles even more closely another anobad, the furniture beetle, Anobium punctatum (figure 115, chapter 5), which also has striate elytra and a 3-segmented antennal club. However, the front margin of the pronotum of the drugstore beetle is much more rounded than that of the furniture beetle, which is more squared off (truncate). There is also a close resemblance in the appearance of the larvae, although that of the drugstore beetle is less hairy.

Life Cycle. The life cycle resembles that of the cigarette beetle.There may be from I generation to as many as 4, depending on the temperature. The drugstore beetle possesses symbiotic organisms that resemble yeasts and produce vitamins of the "B" group, and is therefore not dependent on the presence of this important nutritional factor in its foods. For this reason, it may subsist on foods of very low quality (Hickin, 1964).

Tobacco Moth, Ephestia elutella (Hübner) (Pyralidae)

This cosmopolitan pest of stored tobacco is also a pest of cereals, chocolate, cocoa beans, coffee, cottonseed, dried fruits, flour, nuts, seeds (various), and spices.

Description. The adult moth has a wingspread of 15 to 16 mm. The forewings are brownish gray, crossed with 2 oblique, light-colored bands, while the hindwings are uniformly gray. The mature larva is 10 to 15 mm long, and creamy white, tinged with yellow, brown, or pink. The lightbrown pupa turns nearly black just before the emergence of the adult.

Almond Moth, Cadra cautella (Walker) (Pyralidae)

The larvae of this cosmopolitan insect feed on cereals, cocoa beans, dried fruits, flour, grain, peanuts, seeds (various), and shelled nuts. For some unknown reason, for many years the moth seldom infested dried fruit in California, whereas it evidently did so in other parts of the world (Donohoe, 1946). However, it has finally become a pest of some importance in California on both dried fruits and almonds (H. D. Nelson, correspondence). Cadra cautella is second only to the tenebrionid beetle Tribolium castaneum in its abundance in foodstuffs imported into Great Britain (Freeman, 1964).

The most common insects in the descending order of frequency in imported stored foodstuffs were: Tribolium castaneum, Cadra cautella, Oryzaephilus mercator, Necrobia rufipes, Corcyra cephalonica, Oryzaephilus surinamensis, Lasioderma serricorne, Alphitobius diaperinus, Sitophilus oryzae, Trogoderma granarium, Plodia interpunctella, and Tenebroides mauritanicus.

Description. The almond moth resembles the Mediterranean flour moth, Anagasta kuehniella. It has a wing expanse of 14 to 20 mm. The forewings are mottled gray on most individuals, but on some they are strongly suffused with fawn-colored scales. The moths fly with a conspicuously rapid wing vibration, and dart about quickly. The larvae are so similar to those of the raisin moth, Cadra figulilella (described in the next section), that the two can be distinguished only by an expert (Okumura, 1955).

Whiteshouldered House Moth, Endrosis sarcitrella (L.) [=lactella (Dennis and Shiffermuller)] (Oecophoridae)

This widely distributed insect feeds on a great variety of plant material, such as dry seeds, seed potatoes, rubbish in bird nests, thatch on roofs, fungi on trees, and miscellaneous dry vegetable refuse. It is known to do serious damage in wine cellars by boring into corks, and is also said to infest homes, feeding on dry seeds, meal, and carpets (Austen et al ., 1935). In Great Britain, where the oecophorids appear to be more important pests of stored products than they are in the United States, Endrosis sarcitrella is almost certain to be found wherever broken grain, flour, or other vegetable debris is allowed to accumulate undisturbed (Munro, 1966). This species is widely distributed in California, and in a survey of insects on stored foods and seeds, it was recorded from corn and other grains, mixed feeds, and wheat bran (Strong and Okumura, 1958).

Description. The male and female average 6.3 and 10.5 mm long, respectively. Recently emerged adults can be readily recognized by their white shoulders and prothorax, contrasting with the grayish-whiteforewings that are marked by dark patches. The hindwings are narrowed toward the tips, somewhat like those of the Angoumois grain moth (Sitotroga cerealella), but not so acutely.

Life Cycle. Egg incubation requires 10 to 58 days, the larval period is 38 to 133 days, and the period from egg to adult is 62 to 235 days. The full-grown larva is about 12 mm long, and white, with a brownish head (Austen et al., 1935; Woodrote, 1951; Munro, 1966).

Brown House Moth,Hofmannophila pseudospretella (Stainton) (Oecophoridae)

This is another cosmopolitan species that appears to be especially important as a pest in Great Britain. The larvae feed on book bindings, cereals and cereal products, clothing, corks, dried fruits, dried plants and insects, furniture stuffed with horsehair, furs, grains, herbs, leather, legumes, mohair furniture, paper, seeds (various), and skins. They can cause damage by boring into the corks of wine bottles, causing them to leak. They can also eat their way through nylon, plastics, and the insulation of cables, and are known to infest bird nests (Austen et al., 1935; Bender, 1941; Woodroffe, 1951). Cole (1962) concluded that the brown house moth in "attics and roof spaces" fed on bird and animal droppings, dried corpses, and other dry organic debris. In his experience, carpets were the household articles most often damaged, especially the edges of fitted carpets when they were folded under.

In California, this species is widely distributed, but is not an important pest and is not commonly found in homes. In a survey of pests of stored products, it was reported from cantaloupe seeds, celery seeds, fishmeal, grain, and mixed feeds (Strong and Okumura, 1958). In warehouses in Britain, it is usually an omnivorous scavenger in spilled cereals and flour, but sometimes attacks bulk wheat, bagged flour, and other commodities, and is also found in homes. This moth is believed to owe its persistent survival to its omnivorous habits, its high reproductive capacity, and the resistance to adverse conditions of all stages except the growing larvae, which thrive only in high humidity. However, the larvae can undergo prolonged diapause, during which they are resistant to desiccation (Woodroffe, 1951; Munro, 1966).

Description. The adult moth is bronze-brown, with dark-brown to black flecks on the forewings. The male and female average 8.5 and 14.5 mm in length, respectively. The full-grown larva is white, with a tan head, and is about 6 mm long.

Life Cycle. Egg incubation requires 8.5 to 110 days, and the larval stage lasts 71 to 145 days, both varying greatly with the temperature. The larva spins a cocoon in which it incorporates its foodstuff. The life cycle varies from 192 to 440 days in the laboratory, and takes about 12 months in nature (Woodroffe, 1951; Munro, 1966).

INSECT PESTS ATTACKING DRIED FRUITS AND NUTS

Dried Fruit and Nuts Pests A number of moths and beetles are important pests of dried fruits, although some of them may be equally or even more important as pests of nuts, cereals, and other stored products. Of particular importance are the larvae of certain pyralid moths and the larvae and adults of nitidulid beetles. Some species infest fruit before it is harvested or while it is drying on trays. Others infest fruit principally or even entirely after it is completely dry and in storage or in packages.

(A) Insect Pests of Ripening or Partially Dried Fruits

Raisin Moth, Cadra figulilella (Gregson) (Pyralidae)

This moth is world-wide in distribution, and is one of the most common pests of dried fruits, but it occasionally feeds on cereals and nuts, and also bores holes in oranges on low-hanging branches in Tulare and Fresno counties in California. Damage to dried fruits, particularly raisins, is caused by the larvae feeding on the surface of the fruit and by the resulting pellets and webbing. This species primarily infests fruit in orchards or vineyards or while it is drying. Sound grapes ma:y be attacked, but the larvae usually infest only grapes that have been injured by other causes, chiefly the crackink and crushing of the berries in tight bunches. After the fruit is dry, there is little danger of infestation. Processed fruits in storage, if less than a year old, may sometimes be infested; if older, this rarely occurs, and then only very lightly (Donohoe, 1946).

Description. The adult moth (plate V, 2) is about 10 mm long when at rest with its wings folded. The forewings are grayish and the hindwings are satiny white. Both pairs have a prominent, satiny fringe. The full-grown larvae are about 13 mm long, white, with 4 rows of purple spots along their backs.

Life Cycle. The adults, which live only about 2 weeks, stay inshaded and protected places during the day and are active chiefly in the early evening. The female lays about 350 minute, white eggs, scattering them over the surface of the host fruit. They hatch in about 4 days, and the larvae feed on the fruit for about a month, starting with the ripening of the earliest kinds, such as muIberries. They then enter the soil or some dark retreat to pupate. Breeding may continue from April or May until November.

Driedfruit Beetle, Carpophilus hemipterus (L.) (Nitidulidae)

This beetle is among the most important insects that damage fruit, such as figs, dates, and less often raisins, before they are completely dried and stored. Infestation takes place mainly on cracked or fermenting fruits; sound ones are rarely attacked.

Description. The adults (plate V, 4) are 3 mm long, dull or shiny black, with 2 conspicuous, amber-brown spots at the posterior tips of the elytra and 2 smaller, more obscure spots of the same color near the bases of the lateral margins of the elytra; the antennae and legs are amber; and the surface of the body is finely punctate, each pit giving rise to a hair. In common with most nitidulids, the elytra are short and truncate, exposing the 2 posterior abdominal segments. The antennae are distinctly knobbed.

Life Cycle. The female lays an average of over 1,000 small, white eggs in ripe figs, or on piles of fermenting fruits in orchards or refuse dumps. The incubation period is 1 to 7 days, averaging 2.2. The full-grown larvae are 6 to 7 mm long, white or yellowish, with the head and posterior tip of the body amber-brown. The body is clothed with hairs, and has 2 pairs of large, dorsal tubercles and I pair of small, lateral ones at the posterior end of the abdomen. All larval stages are very active, and try to hide quickly when disturbed. Larval development takes 6 to 14 days. The pupae are robust, oval, somewhat spiny, about 3 mm long, and white or pale yellow, becoming amber when nearly mature. The pupal stage lasts 5 to 11 days. The complete life cycle may vary from a minimum of 15 days in summer to several months in winter. In winter, the adults survive in decaying melons, cull figs, waste dates, and moist raisins; the larvae may be found in such favorable locations as moist cull figs or dates. The pupae generally overwinter in the soil (Simmons et al.,1931; Stickney et al., 1950; Lindgren and Vincent, 1953).

Other Nitidulid Species

Three other species of nitidulid beetles are associated with Carpophilits hemipterus as pests of dried fruits. The corn sap beetle, Carpophilus dimidiatus (F.) (plate V, 4), is about 5 mm long, pitch-black to dull yellow-brown, with the elytra somewhat paler yellow-brown. Haptonchus luteolus (Erichson) is one of the smallest, averaging about 3.5 mm in length. It is yellowish brown, but considerably lighter in color than the preceding species. The pineapple beetle, Carpophilus humeralis (F.) (= Urophilus) (ffigure 195), is entirely black, and is one of the largest of the 4 species found in dried fruits, being 4 to 5 mm long.

(B) Insect Pests of Dried Fruits During Storage

Unlike the pests already discussed, those in this section generally begin their infestations after the fruit has been harvested and dried (usually during storage), particularly if the infested products have been stored for long periods. Certain species that are important pests of dried fruits in storage are not discussed fully in this section, since they are even more harmful to other stored foods. Their habits and biological data are given under more appropriate headings. The acarid mites are important pests of dried fruits, but are considered later under a separate heading.

Indian Meal Moth, Plodia interpunctella (Hübner) (Pyralidae)

In California, this is the most important moth attacking dried fruits in storage and in the home (figure 186). Although it is principally a storage pest, it can also attack fruit before it is dried. Infestations may begin on a ranch where the fruit has been dried and temporarily stored in boxes, and the insects will continue to develop in packing houses unless the fruit is fumigated and stored in insectproof enclosures (Simmons et al., 1931). Because it attacks a wide variety of foods, the Indian meal moth is one of the most common species found in the home. The "white worms" seen in packaged dried fruits are nearly always the larvae of this moth (Donohoe, 1946). Abundant webbing in infested materials is characteristic Of infestations by the Indian meal moth. Its larvae are often found far from infested foods because they usually crawl away from their foods to construct silken cocoons in which to pupate. (The description and life cycle of the Indian meal moth have been discussed earlier in this chapter.)

Mediterranean Flour Moth, Anagasta kuehniella (Zeller) (= Ephestia) (Pyralidae)

The larvae of this species infest dried fruits, and leave their webbing. As with the Indian meal moth, they crawl away from the food to construct pupal cocoons, but usually near the infested product. They may also migrate to other parts of the pantry or kitchen, or even elsewhere in the house.

Almond Moth, Cadra cautella (Walker) (Pyralidae)

This cosmopolitan insect, described earlier in the present chapter, was once referred to as the "fig moth"; because early investigators in California believed it to be an important pest of dried fruits, particularly figs. However, despite being widely recorded in the world's literature as a major pest of dried fruits in storage, Donohoe (1946) and other investigators, after examining thousands of moths reared from dried fruits from field and storage areas throughout California and parts of Arizona, found no instance of infestation by this particular species. In fact, the moths were not even found in dried fruits when they were stored close to almonds, the favored hosts. The earlier records of the moths on dried fruits in California were believed to be results of misidentification. Their absence during a long period was considered to be a biological mystery. As already stated, Cadra cautella is again assuming some importance as a pest. According to the USDA Dried Fruit and Tree Nuts Insect Investigation Laboratory in Fresno, C. cautella is infrequently observed infesting raisins or other dried fruits and nuts in California (H. D. Nelson, correspondence).

Driedfruit Moth,Vitula edmandsae serratilineella Ragonot (Pyralidae)

This insect develops readily in dried fruits, preferably slightly fermented ones, as well as in rotting bee combs. It has also been found in the cells of a carpenter bee, Xylocopa tabaniformis orpifex, where the larvae hid probably fed on pollen (Linsley, 1943a). The adults are likely to be found in the dark corners of storage bins of dried fruit or between rows of stacked boxes.

Description. The mottled-gray moths are nearly twice as large as the Indian meal moth. The larvae, 18 mm long, are white or pinkish except for the head, prothoracic shield, and anal plate, which are brown. They are larger than those of the Indian meal moth, but have the same habit of prepupal migration (Essig, 1926; Donohoe, 1946). They closely resemble the larvae of the raisin moth, Cadra figulilella (Okumura, 1955).

Stored Nut Moth, Aphomia gularis (Zeller) (Pyralidae)

This moth occurs principally in India, China, and japan, and is found occasionally in Britain, continental Europe, and North America. It was first reported from North America in 1919 in a shipment of peanuts to California that originated in China. It was reported again in 1930 and 1931 from San Jose, California, under conditions that indicated it was infesting prunes. Its larval food appears to be limited to seeds, flour, nuts, and dried fruits. It is found in California somewhat rarely. It has been reared from walnuts in Montreal, Canada. (It is included in this section because nuts do not form its only diet.)

Description. The forewings are 10.5 mm long and 3 mm broad, and the length from head to tip of abdomen is about 10.5 mm. The forewings are light yellowish brown, and the hindwings are lighter. The thorax, abdomen, and legs are of the same basic color as the forewings.

Sawtoothed Grain Beetle, Oryzaephilus surinamensis (L.), and Merchant Grain Beetle, O. mercator (Fauvel) (Cucujidae)

These beetles (figures 191 and 192) infest dried fruits, usually after they have been stored for long periods. (They have been described under "General Feeders" earlier in this chapter.) The lower the moisture content of the fruit, the more severe the infestation can be. Without adequate protection, dried fruits, particularly raisins, can be so severely damaged by these pests as to be virtually worthless. They readily penetrate the packages in which foods are kept. The small, brown, flattened adults are only about 3 mm long, and the prothorax bears 6 sawlike teeth on each side (see figure 192). It is difficult to distinguish one species from the other, and the relative impprtance of the two has not yet been determined in regard to dried fruits.

Flour Beetles Tribolium spp. (Tenebrionidae)

These beetles, Tribolium confusum Jacquelin duVal and T. castaneum (Herbst), described earlier in this chapter, rarely infest dried fruits severely, but both species can survive in them, and care should be taken to prevent infestation, particularly when dried fruit is stored or shipped in close proximity to products that are even more subject to infestation.

Rusty Grain Beetle, Cryptolestes ferrugineus (Stephens) (= Laemophloeus) (Cucujidae)

This very small cosmopolitan beetle (also mentioned earlier) is usually found in stored grain and other foodstuffs and under the bark of trees. It can also be found in stored fruits, and is sometimes the dominant species in moldy ones, especially in winter. The adults frequently infest fallen, moldy, drying fruits, particularly figs.

(C) Moths Attacking Walnuts and Almonds in the Orchard

Persian walnuts and almonds are grown commercially in the United States, principally in areas on the Pacific slope in California. The nuts can become infested in the orchard with the larvae of certain moths. The same species may also infest stored nuts, and can be accompanied by others that attack the nuts only after they are in storage. Insects found infesting walnuts or almonds in the home usually come from nuts obtained from dooryard trees and stored indoors. Also, moths emerging from the nuts outdoorssometimes become accidental intruders in the home.

Codling Moth, Laspeyresia pomonella (L.) (= Carpocapsa) (Olethreutidae)

This is an age-old cosmopolitan pest of apples. It was not found in walnuts until 1909, and had become a serious pest in a limited area of southern California by 1918. It is now widely distributed on walnuts, and annual treatment with pesticides is required.

Description. The adult moth (figure 196) has a wingspan of about 20 mm. The forewings are brownish, with several gray or paler cross lines and a dark-golden and coppery patch at the tips. The hindwings are paler. The outer margins of the wings are fringed with hairs.

Life Cycle. The female lays flat, white, discoidal eggs, about 1 mm in diameter, singly on foliage or nuts. The full-grown larvae are about 20 mm long, yellowish or pinkish, with the heads and thoracic shields brown. They pupate in any hidden retreats in white, felty cocoons. The pupae are light amber to dark brown, and are about 13 mm long. In the larval stage, the winter is passed in cocoons (figure 196) under loose flakes of bark, in old pruning cuts, tree crotches, in litter on the ground, or in other protected places. Pupation occurs in early spring, and the first brood of moths appears in April or May. There may be a complete second generation within any year, depending on seasonal temperatures, and in some years even a partial third.

Cultural Control. It is helpful to destroy the hiding places of the hibernating larvae by scraping the loose bark off old trees and removing prunings and other rubbish from the ground.

Filbertworm, Melissopus latiferreanus (Walsingham) (Olethreutidae)

This pest, also known as the Catalina cherry moth, was formerly known to infest only the Catalina cherry (Prunus lyonii) in southern California, and the large, green galls of the blue oak (Quercus douglasii) in central and northern California. Investigations conducted in 1944 showed that this insect was an important pest of walnuts in the Sacramento Valley (Bacon et al., 1948), and it now attacks most varieties of walnuts throughout the state. It may also attack acorns and hazelnuts (filberts). It is likely to become destructive only in areas where one of its native hosts, the oak-apple gall, is produced in abundance; the moths migrate from oaks to walnuts.

In 1968, the author received many larvae and cocoons of the filbertworm collected from a deeppiled woolen rug in a home in San Marino, California. The larvae had not been feeding on the rug, but appeared to have originated from infested walnuts in or outside the house. There are many oak trees near-by.

Description. The adult moth (figure 197) has a wingspread of about 13 mm. It is pale or dusky bronze, and has a complete, broad, coppery median band and a broken postmedian coppery band on each forewing.

Life Cycle. The whitish, disklike eggs are laid in the fruit of the host plant or on oak galls. The full-grown larvae are about 20 mm long. They resemble the larvae of the codling moth, but in the later instars they become uniformly creamy white, while the codling moth larvae become pinkish. The filbertworm larva's head is a clear amber color, while that of the codling moth larva is brown.

Although the larvae are able to feed on the walnut kernel (figure 197) at any stage of its development, they cannot gain access to it until cracks appear in the husk at the time of maturity. Therefore, the nuts are not damaged until late August or September. If a continuous food supply is present, as when walnuts are grown near oak trees, there are 2 broods per year and a partial third brood (Bacon et al., 1948).

Navel Orangeworm, Paramyelois transitella (Walker) (= Myelois venipars Dyar) (Pyralidae)

This insect was known for many years as a scavenger in cracks or wounds of navel oranges. Beginning about 1943, it began to attack walnuts, depositing its eggs on the green husks, and it now occurs throughout most of the nut- or fruitgrowing areas of California. It is also found in many varieties of fruits as a scavenger, developing in those that are mature but injured or mumm fied. It is considered to be a primary pest of walnuts and almonds. The larvae can enter the sound nuts after their hulls have cracked, thus causing the damage a few weeks before harvest. Some larvae only rasp the surface, while others bore deeply into the nut meat. Webbing produced by the larvae is sometimes so profuse as to hide any unconsumed nut meat (Wade, 1961). When almonds are infested and damaged in th I e field by the navel orangeworm, peach twig borer, or codling moth, they are more subject to attack in storage by the merchant grain beetle (Spitler and Hartsell, 1967).

A Related Species. Another moth, Ectomyelois ceratoniae (Zeller), with similar habits, is the most important pest of stored almonds in Israel. It also attacks other nuts, dried fruits, stored carob pods (Ceratonia silique) and stored seeds in Israel, as well as walnuts in South Africa (Calderon et al., 1969). It is said to infest dried fruits, seeds, and nuts from widely separated areas in Europe, Africa, and "America" (Corbet and Tams, 1943).

Description of the Navel Orangeworm. The adult (plate V, 3; figure 198) is silvery gray, with irregularly narrow to broadly wavy lines on the forewings. The hindwings are uniformly light, except for a darkening at the tips and along the veins. The females average 10.9 mm in over-all length; the males, 9.7 mm. The larvae (figure 198) are at first reddish orange and, after the first molt, pinkish orange to cream-color. As they develop, they may be entirely cream-colored if they are reared on oranges. If the food is contaminated with spores of black mold, the intestinal tract will appear black. Full-grown larvae range from 13 to 19 mm in length. The pupae are dark brown, with sutures clearly evident. They range from 7.25 to 12 mm in length, those of the females averaging larger (Wade, 1961).

Life Cycle. The larvae and pupae overwinter in old nuts left on the trees. The adults emerge in the spring, and the female lays her first eggs in April on old, sticktight nuts remaining on the trees or on twigs fairly close to the old nuts. The oval, flattened egg has many ridgelike marks on the surface. It is at first lustrous creamy white, but changes to pink and finally to reddish orange. Infestation becomes evident sometime in August, for the current crop is attacked only after the hulls have split. The infestation increases until the nuts-are harvested (Wade, 1961).

Cultural Control. Early and complete harvest of nuts is desirable in order to minimize the possibility of their becoming infested. Sticktights Nhould be removed from the trees and destroyed, as well as nuts left lying on the ground or in tree crotches. Good codling moth control is an aid in the control of the navel orangeworm, which often enters nuts through holes made by codling moth larvae. There is no known effective chemical control for the navel orangeworm.

Almond Moth, Cadra cautella (Walker) (Pyralidae)

This moth has already been discussed as a pest of dried fruits. It derived its common name from its former importance as a pest of almonds in California. Then for many years it was seldom seen, but is now observed in increasing numbers on almonds as well as dried fruits.

Peach Twig Borer, Anarsia lineatella Zeller (Gelechiidae)

This moth is a serious pest of peaches, almonds, apricots, nectarines, plums, and prunes. The larvae injure the buds and young twigs and also enter the fruits, particularly those of the almond. They are also known to infest walnuts. The fullgrown larvae average 10 mm in length, and are reddish brown except for the yellowish-white intersegmental membranes and the black head. The pupae are 6 mm long, naked, smooth, and dark brown. The adults are about 8 mm long, steel-gray, with white and dark scales. The wings are narrow and fringed, with an expanse of 12 to 15 mm, and are held rooflike when at rest.

Fruittree Leafroller, Archips argyrospilus (Walker) (Tortricidae)

This tortricid occurs on many varieties of fruit trees, feeding principally on foliage, but the larvae are occasionally found in walnuts. They are about the same size as those of the codling moth, but- are greenish, while the codling moth larvae are often pink.

(D) Storage Pests of Walnuts and Almonds

Unless the field-insect pests of walnuts and almonds just discussed are controlled, they will continue to feed within the shells, and may completely destroy the nut meats. In addition, these insects create conditions favorable to the establishment of many secondary feeders among storage pests, such as Tribolium confusum, T. castaneum, Oryzaephilus surinamensis, and O. mercator. The Indian meal moth, Plodia interpunctella is a primary feeder among the storage pests, and can become a problem if the nuts are stored more than 30 days (Spitler and Hartsell, 1969). (See figures 186,191, and 192.)

MITE PESTS OF STORED FOOD PRODUCTS

Mite Pests
  1. ACARID MITES
  2. PREDACEOUS MITES

ACARID MITES (ACARIDAE) (= TYROGLYPHIDAE)

Acarid Mite Pests

There are several species in this cosmopolitan family that are of importance chiefly as pests of stored foods, flour, grain, seeds, and bulbs, feeding on these products or the fungi that develop on them. These mites are mostly very minute, almost colorless, with the body bearing a few long setae, and with the legs terminating in 1 claw and usually a sucker. When very abundant,, the mites and their cast skins form a buff-colored dust and give rise to a characteristic odor. The living mites move slowly away from a source of light. An interesting characteristic of these mites is a nymphal resting stage (hypopus), during which they take no food but attach themselves to other mites, insects, and humans by means of suckers, and are thereby transported to other suitable places for development, where they drop off, molt, feed, and develop to the adult stage. The hypopus may be resistant to fumigants. However, the "cheese mites" Tyrophagus casei and T. longior do not have a hypopial stage. An exhaustive treatise on the morphology and biology of the mites that may be found in stored foods was written by Mrs. A. M. Hughes (1961).

Prolonged storage of products subject to infestation without cleaning of pantries and shelves where such materials are placed may result in serious infestations, for these mites can subsist on organic debris in cracks, crevices, and corners, and are readily spread to other areas.

Control methods for acarid mites are given under "Control of Pantry Pests" at the end of this chapter.

Grain Mite, Acarus siro L. (= Tyroglyphus farinae De Geer)

The grain mite (figure 199) is the most important and best known of the mites infesting grain and flour, but can also infest other stored food products. In severe infestations, grain mites are responsible for the "mite dust" on the surface of cheese or on the floor at the bases of stacks of flour or wheat sacks. Although the bodies of the mites are almost colorless, their legs are brown, so the"mite dust" has a brownish tinge. If the mites are crushed, their "minty" odor is easily recognized. Whereas Acarus siro is widely distributed in temperate zones, it occurs in the tropics only through repeated introductions with grains and foodstuffs. It is not an important pest in hot climates, if it persists at all (Solomon, 1962).

Description. This mite is pearly white, with legs varying in color from pale yellow to reddish brown. The male is 0.32 to 0.42 mm long, and the female, 0.35 to 0.65 mm. The mite can be distinguished from members of other genera because of the femur of the male's foreleg being enlarged and bearing a stout spine ventrally, a characteristic of the genus Acarus (A. M. Hughes, 1961).

Life Cycle. In a day, a female may lay 20 to 30 oval, smooth, white eggs, 0.12 mm long, singly or at random on the food material. Under favorable conditions, the female can lay up to 800 eggs in her lifetime (about 40 days). The larvae feed and grow rapidly for 3 days, then lie motionless for 2 days before molting. The life cycle may require 17 days at a favorable temperature ranging from 64 to 71 °F (18to 22 °C), but during the winter at 50 to 60 °F (10 to 16 °C), it requires 28 days (A. M. Hughes, 1961). Acarus siro does not have tracheae, so the cuticle must be permeable to gases and therefore also to water vapor. Although the epidermis and cuticle obviously have some ability to regulate water balance, this does not suffice to prevent a lethal rate of water loss below 60% relative humidity, and the mites cannot survive at such humidities (Solomon, 1962; Munro, 1966). The distribution of the grain mite in stored grain is conditioned by the relative humidity of the air between the kernels, which in turn depends on the water content of the grain. The mite avoids relative humidities below 75% and above 85% (Knülle, 1963a).

Curry (1971) found wholewheat flour to be the best substrate for rearing this species. In 5 plastic vials, each containing 3 grams of foodstuff plus mold inhibitor, he reared a total of 26,055 mites in wholewheat flour, 6,140 in cornmeal, 1,395 in polished rice, 68 in white flour, and 48 in enriched white flour in a period of 30 days. He concluded that white flour, in the absence of mold, was not a suitable food substrate for A. siro. Fungi not only attract these mites to a food, but are themselves good food sources. On unbroken grain, fungi serve another function, for the mites cannot feed on unbroken kernels. The fungi weaken the hull, permitting access to the germ, where the mites can feed and reproduce (Thomas and Dicke, 1971).

The grain mite is commonly found in bird nests around houses and stores, and it is believed that birds aid in its dispersal. Rodents and other mammals also probably contribute to dispersal, as well as humans on their shoes and clothing (Woodrote, 1953). The mites are common in grocery stores, and are usually the culprits responsible for a severe dermatitis known as "grocer's itch". In fact, probably any acarid mites could cause dermatitis on the body of a sensitive person (Pratt, 1963; Busvine, 1966).

Cheese Mite, Tyrophagus casei (Oudeman)

These cosmopolitan mites are common in stored food, cheese, grain, damp flour, old honeycombs, and insect collections. They can eat out small holes in cheese, and have been cultured for addition to Altenburger cheese to impart a characteristic "piquant" taste. When the cheese is covered with a grayish powder, consisting of enormous numbers of living and dead mites, cast skins, and feces, it is considered by some people to be "ripe" and particularly delectable (A. M. Hughes, 1961; Busvine, 1966).

Biology. This species, like others of the genus, has at least 4 pairs of long bristles trailing from the hind end of the body. It is translucent, but has tan-colored legs and mouthparts. The males are 0.45 to 0.55 mm long, and the females, 0.50 to 0.70 mm. The life cycle requires 15 to 18 days at 23 °C (73 °F) and 87% relative humidity.

Tyrophagus longior (Gervais)

These mites are commonly associated with grain, hay, and straw, but are also found on cheese. In the United States, they are not so serious a problem as Acarus siro (A. M. Hughes, 1961). Tyrophagus longior has been implicated in human pulmonary, urinary, and intestinal acariasis (Baker et al., 1956).

Biology. The mites are translucent like the foregoing species, but the legs and chelicerae are more deeply tan. The males are 0.33 to 0.53 mm long, and the females, 0.53 to 0.67 mm. The life cycle requires 14 to 21 days.

Mold Mite, Tyrophagus putrescentiae (Schrank) (= lintneri Osborn)

This is one of the most destructive pests of stored products. According to A. M. Hughes (1961), the mold mite is found most frequently on products having a relatively high fat content, such as linseed, dried egg yolk, peanuts, cheese, ham, herringmeal, and copra, but occurs on dried banana, spilled wheat, oats, barley, and flour, and is also a pest on mushrooms. Linsley and Michelbacher (1943) recorded this mite in California, under the synonym Tyroglyphus americanus Banks, as occurring in enormous numbers in cereals and cereal products. They stated that the mites sometimes caused considerable concern and annoyance when infesting stored products in homes, and were responsible for the severe dermatitis called "grocer's itch" when attacking humans who handled infested materials. The mites also cause "copra itch" familiar to persons handling infested copra dust (A. M. Hughes, 1961). As already stated under Acarus siro, itches can also be caused by other acarid mites, among which A. siro is very notable.

Biology. This is a small, translucent mite, with almost colorless chelicerae and limbs. The males are 0.28 to 0.35 mm long, and the females, 0.32 to 0.41 mm. It is more slender than other acarids, and the long setae do not project so stiffly from the surface of the body. The life cycle requires 2 to 3 weeks at 23 °C (73 °F) and 87% relative humidity.

Driedfruit Mite, Carpoglyphus Iactis (L.) (= Acarus passularum Hering)

This species is found principally on dried fruits, jams, and products containing lactic, acetic, or succinic acids. It has been found in honeycombs, fruit drink residue, senna confections, wine clinging to pieces of cork or forming a floating scum on the surface, rotting potatoes, flour, dried-milk powder, and caramel used in manufacturing sweets.

It seems to be particularly attracted to substances that are starting to ferment (A. M. Hughes, 1961). In California, this species is sometimes found in enormous numbers on a variety of dried fruits, imparting a disagreeable odor. It has also been observed on cured hams and the pollen paste of bees (Essig, 1926; Simmons et al., 1931; Donohoe, 1946). Carpoglyphus lactis can cause "driedfruit mite dermatitis" (Baker et al., 1956).

Biology. This oval, slightly flattened mite is translucent, except for the color of the contents of the alimentary canal, which can be seen through the body wall. The legs and mouthparts are pinkish. There is no transverse suture dividing 2 body regions, as with certain other species. The 2 sexes are 0.38 to 0.40 mm long, and are similar in appearance. The females can lay 25 to 30 eggs in a week, attaching them to the substrate by means of a stalk, and can then survive another 35 to 45 days.

Thyreophagus entomophagus (Laboulbene)

This mite, found on dried fruits and jams, has an elongate and oval body, a colorless, shiny cuticle, and pale-brown, stumpy legs. The males are 0.30 to 0.45 mm long, and the females, 0.45 to 0.60 mm. It has been recorded from England, France, Germany, Italy, Russia, and the United States (A. M. Hughes, 1961).

Glycyphagus destructor (Schrank)

This cosmopolitan mite is one of the most common species on stored products, often in association with Acarus siro. A. M. Hughes (1961) stated: "It lives in stores of grain, any kind of cereal, linseed, dried fruit, hay, cheese, straw, rodent and bumble bee nests." [The last 2 records probably represent its natural habitat.] This species is considered to be strictly mycophagous (fungus-eating), but is also attracted to sugar, and will live on fresh wheat germ.

Biology. The body is pearshaped, being somewhat constricted behind the fourth pair of legs. Minute papillae give the cuticle a dull-whitish coloration. The males are 0.35 to 0.50 mm long, and the females, 0.40 to 0.56 mm. Pectinate (feathery) hairs are characteristic, and are particularly long on the posterior third of the body. The legs are long and thin. The mite moves with a characteristic jerking gait.

Grocer's Itch Mite, Glycyphagus domesticus (De Geer)

This mite (figure 199), also called "house" or "furniture" mite, is world-wide in distribution, being found in "flour, wheat, hay, linseed, tobacco, sugar, cheese, and bee frames, in bees' and birds' nests, and in the sweepings from barns. It will increase to enormous numbers on rush furniture and on upholstered chairs stuffed with green Algerian fibre" (A. M. Hughes, 1961). As the common name implies, the mites often cause "grocer's itch," in common with some other acarids just noted. (See also, chapter 10.)

Biology. Live mites of this species can be distinguished from Glycyphagus destructor by having a more rounded body and by a uniform, unhurried gait in contrast with the jerking progress of the latter. The long hairs oii the body and legs are less coarsely pectinate than those of G. destructor, and in life they radiate stiffly from the surface. Like the related species, this mite has long legs with tapering segments. The males are 0.32 to 0.40 mm long, and the females, 0.40 to 0.75 mm (A. M. Hughes, 1961).

PREDACEOUS MITES

Predaceous Mite Pests

Together with the acarid mites in stored products, one can often find their predators. Under conditions of proper temperature and humidity, these predators can greatly suppress acarid mite infestations, but in the meantime their presence in stored food is likewise a nuisance, and some species also cause dermatitis in humans. Prominent among the predaceous mites are those of the family Cheyletidae, an extensive review of which was prepared by Summers and Price (1970). The family Pyemotidae also figures prominently.

Cheyletus eruditus (Schrank) (Cheyletidae)

This is one of the most common predaceous mites. Like most predators, it is a solitary animal, and doesn't gather in masses like its victims. It moves about rapidly. A striking structural character is the pair of stout, pincerlike pedipalps used to seize its prey. It probably injects venom into its victim, for the latter is soon paralyzed. It then takes about a half hour to suck the disabled prey dry. Male mites are rare; reproduction is mainly parthenogenetic. The females are 0.45 to 0.62 mm long. The efficacy of this species as a predator is limited by the fact that it requires moderately high temperatures. It reduced the grain mite, Acarus siro, practically to extinction in grain at 25 °C (77 °F) and 70 or 90% relative humidity, but was unable to prevent its increase at 5 to 10 °C (41 to 50 °F). Acarus siro can increase in temperatures at which Cheyletus eruditus is static. However, the latter can live when the moisture content of the grain mite's food is too low to allow reproduction. Under such a condition, the predator may completely suppress A. siro. In summer, C. eruditus tends to be dominant, but A. siro is dominant under the moister and cooler conditions of winter (Solomon, 1962; Kniille, 1963b). Some species of Cheyletus may infest man and cause localized skin troubles (Horsfall, 1962).

Acarophenax tribolii Newstead and Duvall (Scutacaridae)

The females of this mite are parasites of flour beetles (Tribolium spp.), as the specific name indicates. They are 0.16 to 0.19 mm long before becoming gravid and 0.24 to 0.29 mm in diameter when gravid. The nongravid female is round and arched, tapers slightly toward the posterior end, and is yellow. With their styletshaped chelicerae, the mites pierce the cuticle of their host where it is soft, beneath the second pair of wings, and suck the body contents. Then, with bodies distended with embryos, they leave the victim. About 14 or 15 mites develop within the female's body, and only one of these is a male, which never leaves. Therefore, the females are probably all fertilized before leaving the enlarged genital opening. The mother dies as soon as the young have emerged (A. M. Hughes, 1961).

Straw Itch Mite, Pyemotes ventricosus (Newport) (Pyemotidae)

The females of this mite are ectoparasites 6n the immature stages of many arthropods, including pests of stored products. This species is discussed more fully in chapter 9, under "Mites" because of its primary importance as a cause of human dermatitis.

The scutacarids and pyemotids are closely related. Pyemotes ventricosus rivals Acarophenax tribolii in the peculiarity of its biology. In both species, the mites reach maturity within the mother's body, but in the case of P. ventricosus the male emerges to fertilize the females after they have left the body (A. M. Hughes, 1961; Munro, 1966).

INSECT CONTAMINATION OF MILLED CEREAL PRODUCTS

From the great number of storage pests discussed in this chapter, the reader may conclude that the identification of all species would be a truly formidable task. Then, how much more difficult would be the identification of insect fragments in canned, milled, or otherwise processed foods! However, specialized methods have been found to accomplish this task (Harris, 1946, 1955; Harris et al., 1952, 1953, 1969).

Detection of contamination by rodents, insects, mold, and sometimes yeasts and bacteria can often be accomplished by simple examination, preferably aided by the use of a hand lens or microscope. For example, live insects or the webbing of moths are obvious evidences of insect infestation. Insects may also leave characteristic feeding marks on the various food products, or leave their frass (excreta, cast skins, or particles of food) on them. The fecal pellets of rodents are also easily identified. If flour is sifted through a No. 64 wire screen, most of the eggs, larvae, and adults of any insects that may be present can be removed. Photographs of the hundreds of types of insect fragments from the many species of all orders and families of insects that commonly contaminate stored foods may be found in a monumental treatise on the subject by Kurtz and Harris (I962).

Insect mandibles are resistant to grinding, and may be recovered from ground food products and examined microscopically. Kurtz et al.(1952) published a key for the identification of the mandibles of common insects infesting stored grain, recovered from various food products. Heuermann and Kurtz (1955) published a paper on the identification, on the basis of elytral patterns, of 20 insects associated with food products. Even small pieces of elytra can be used to identify insect species.

If food contamination is severe, the nature of the contaminant can sometimes be determined by its odor. Tribolium and Rhyzopertha produce a musty, penetrating odor, and tyroglyphid (acarid) mites produce a distinctive, sweet "minty" odor.

With low-voltage X rays, it is possible to reproduce an image of the amount of tissue removed from seeds by insects. Live insect larvae can be detected in a radiograph because larvae contain much water and X rays do not readily penetrate it. Pupae are less readily visible, and adult insects are practically invisible. Dead larvae can occasionally be seen, but not dead pupae or adults.

Various methods have been devised to isolate the contaminant. Some are based on the insolubility of the contaminant (or a product thereof) in solvents, chemical reagents, and enzymes that can dissolve the food product. Some are based on differences in size of the food and the contaminant. Others are based on differences in specific gravity or on selective wetting. The Waldman trays procedure, for example, is based on the fact that animal hairs, insects, and insect fragments are wet by oil, and plant material is wet by water, and the specific gravity of oil is less than that of an aqueous medium. Several of these principles of isolation are usually combined in an isolation and detection method (Harris et al.,1969).

CONTROL OF PANTRY PESTS

For all pests, control begins in the field, but this is particularly true of the pests of dried fruits. The pests that infest injured fruits on the tree or vine or while the fruit is on drying trays can be partially controlled by eliminating near-by breeding places, such as waste fruits, or by protecting drying trays from infestation. Raisins dried on trays containing about 100 mg of malathion per sq ft (929 sq cm) are protected from insects during drying and storage (Nelson, 1967; Nelson et al.,1967).

Figs are fumigated with methyl bromide for the control of field pests at the beginning of storage, and again every 30 to 60 days to control storage pests. Many pests of dried fruit are removed during processing, sorting, and cleaning before it is packaged. Malathion dust has proved to be effective in protecting almonds (Spitler and Hartsell, 1967), walnuts (Spitler and Hartsell, 1969), dried figs (Spitler, 1969), raisins (Spitler and Hartsell, 1970), and prunes (Spitler and Clark, 1970) for as long as a year in storage. Phostoxin tablets, placed on paper plates on large stacks of natural raisins in sweat boxes, have been found to give complete kills of merchant grain beetles (Oryzaephilus mercator), Indian meal moth larvae (Plodia interpunctella) and raisin moth larvae (Cadra figulilella) at dosages as low as 5 tablets per 1,000 cu ft (28 cu m) when the gas was allowed to remain for 6-day periods. Effective treatments leave residues of less than the 0.01 ppm federal tolerance.

Some pests, such as the sawtoothed grain beetle and Indian meal moth, attack dried fruits only after they are in storage or in the home pantry. Regardless of the source of infestation, the homeowner's efforts must be directed toward the detection and removal of infested material.

Methyl bromide fumigation is used to control both field and storage insects in the"in-shell" nuts. However, there is some danger that with repeated fumigations, the tolerance of 200 ppm of methyl bromide may be exceeded. Recent preliminary investigations with malathion, patticularly as a dust in a "tumbling" method of treatment, indicated that this insecticide, applied to the surface of the walnut shell, would protect the nut meat from insect attack. The malathion caused no differences in flavor or odor, but the heaviest dust treatment resulted in a lighter color of the shell (Spitler and Hartsell, 1969).

In January, 1972, the Environmental Protection Agency's Pesticides Regulation Division registered the use of malathion 57% E for the protection of stored in-shell almonds from the Indian meal moth and merchant grain beetle. A suitable mechanical spray applicator should be used that regulates the rate of application of the insecticide to the flow of the almonds. Tle spray nozzle should be shielded against wind and air currents. A mist so fine that it drifts away should not be used. Four fluid ounces of the emulsifiable concentrate are enough to treat 5 tons of almonds (about 120 ml for 4,500 kg).

Some infestations of packaged food originate in the food-processing plant or warehouse. Broken packages should not be purchased, or should be exchanged for unbroken packages when discovered, for the chance of these being infested is greater than for perfectly sealed ones. Even iealed packages can be penetrated by some species of insects. The Food and Drug Administration currently approves only synergized pyrethrins for the treatment of packages to make them insect repellent.

Opportunities for packaged foods to become infested in the home are numerous. Pantry pests, such as various species of beetles, moths, psocids, and mites, may gain access to a home in old furniture, rugs, drapes, bedding, and other products of plant or animal origin. Some pantry pests breed in the nests of rodents or insects, or in dumps or other places where by-products and waste from processing plants are deposited. They may enter the home under doors, through broken or loosefitting screens, through fireplace flues, or around utility pipes. Some may breed in spilled food products on pantry shelves, particularly material in cracks, crevices, and corners that may have been overlooked for long periods. Periodic cleaning of the shelves helps to prevent infestation of stored food products by pantry pests.

Infestations are most likely to occur in packages that have been opened for the removal of a portion of the contents and then left unsealed for long periods. Some of the pests may find their way into other food packages, but even those in a single package may become so numerous that large numbers may find their way into every suitable material in the home, and will eventually crawl over floors, climb up walls, and gather about windows. Control of pantry pests requires that all sources of infestation, usually opened or damaged packages of such things as cereals, dried fruits, nut meats, flour, meal, cornstarch, crackers, breakfast foods, dehydrated foods, macaroni, chocolate, cocoa, dry soup mixes, spices of all kinds, dry dog food, or birdseed be found and destroyed. If the pests have already begun to migrate from the original and most obvious source of infestation, all exposed foodstuffs should be thoroughly examined. If there is any doubt as to whether or not they are infested, they should be destroyed. If insects are suspected in packaged food products but cannot be found, the packages can be placed in plastic bags for a few days. Occasional inspection of the transparent bags will reveal any insects that may have escaped.

Materials believed to be uninfested should be kept in tight containers, such as jars or tins with tight-fitting lids. Then for several weeks, food products subject to insect attack should be purchased only in quantities that can be consumed quickly without prolonged storage. Cheeses have been dipped in wax to provide a complete protective coating against mites. If only a small, incipient infestation of insects has been noted, the removal of the source of infestation may be all that is required for control. If the insects have had the opportunity to become widely distributed, it may be desirable to remove all the pantry contents, clean the shelves, and spray them with a safe and approved insecticide.

Residual sprays of 2% chlordane, 2% malathion, 1% diazinon, or 0.5% lindane are generally effective when applied on shelf surfaces, thoroughly treating all cracks and crevices. Malathion is sometimes used because of its low mammalian toxicity, but even "odorless" malathion leaves an odor that many people consider to be objectionable. Space sprays containing pyrethrins are useful for the rapid, elimination of flying moths, but they have very short residual activity. Resmethrin (SBP-1382®), synergized with piperonyl butoxide, has been found to be effective against a strain of red flour beetles (Tribolium castaneum) that was highly resistant to pyrethrins.

Ham and cheese may be protected against cheese skipper infestation by sanitation and flyproofing. The latter requires tight-fitting doors and 30-mesh wire or plastic screen, as well as residual sprays applied to walls and floors. Certain types of bags have been found to protect hams from infestation (Fulton, 1953). Cheese can be protected with cheesecloth and paraffin.

Infestations of acarid mites can be prevented by keeping their potential environment moderately dry. The mites are destroyed by a temperature of 130 °F (54 °C) for several hours (Linsley and Michelbacher, 1943). When chemical control is attempted, infested foodstuffs should first be removed and destroyed and the shelves cleaned. Sprays of pyrethrum and piperonyl butoxide or other suitable synergist have been successfully used against the cheese mite. Ethylene dibromide was found to be outstandingly effective as a fumigant against 2 species of mites found infesting packages of chapatties, a common baked wheat preparation in India. It was 46 and 17 times more effective in controlling Tyrophagus putrescentiae (Schrank) than methyl bromide and phosphine (normally generated from Phostoxin tablets), respectively, and 4 and 6 times more effective against Caloglyphus krameri (Berlese) than methyl bromide and phosphine, respectively (Muthu et al.,1970).


Figure Captions

Fig. 177. Granary weevil, Sitophilus granarius. A, adult; B, lateral view of adult; C, larva; D, ventral view of pupa; E, lateral view of pupa; F, rice weevil, Sitophilus oryzae (adult). (From Linsley and Michelbacher, 1943.)

Fig. 178. Lesser grain borer, Rhyzopertha dominica. A, adult; B, pupa; C, larva. (From Linsley and Michelbacher,1943.)

Fig. 179. Adult of lesser grain borer, Rhyzopertha dominica (top),and adult and larva of drugstore beetle, Stegobium paniceum. (See the latter under "General Feeders.")

Fig. 180. Angoumois grain moth, Sitotroga cerealella. A, adult in normal resting position; B, adult with wings spread; C, larva; D, pupa. (From Linsley and Michelbacher, 1943.)

Fig. 181. Pink scavenger caterpillar, Sathrobrota rileyi.

Fig. 182. Lesser mealworm, Alphitobius diaperinus.

Fig. 183. Flat grain beetle, Cryptolestes pusillus. A, adult male; B, head and antennae of female; C, pupa, ventral view; D, pupa, lateral view, E, pupa case cut open, showing pupa within; F, larva. (From Linsley and Michelbacher, 1943.)

Fig. 184. Broadnosed grain weevil, Caulophilus oryzae. A, adult; B, adult and larvae in an avocado seed; C, injury to avocado seeds.

Fig. 185. Mediterranean flour moth, Anagasta kuehniella A, adult in normal resting position; B, adult with wings spread; C. larva; D, enlarged drawing of 2 segments of larva in the region of the proleg; E, pupa. (From Linsley and Michelbacher, 1943.)

Fig. 186. Indian meal moth, Plodia interpunctella A, eggs; B, larva; C, pupa case and pupa; D, adult. (Courtesy Stennett S. Heaton.)

Fig. 187. Spider beetles. A, Ptinus ocellus; B, Ptinus fur (male); C, Ptinus fur (female); D, Ptinus villiger; E, Ptinus clavipes (male); F, Ptinus clavipes (female); G, Gibbium psyllodes; H, Trigonogenius globulum I, Mezium americanum, J, Mezium affine. (Courtesy C. S. Papp.)

Fig. 188. Bean weevil, Acanthoscelides obtectus. A, adult; B, lateral view of head and thoracic region; C, larva; D, pupa. (From Linsley and Michelbacher, 1943.)

Fig. 189. Three species of Necrobia that infest dried and smoked meats. A, redlegged ham beetle, Necrobia rufipes; B, Necrobia violacca; C, Necrobia ruficollis (From Papp, 1959.)

Fig. 190. Cheese skipper, Piophila casei. A, eggs; B first-instar larva; C, third-instar larva (dorsal); D, third-instar larva (lateral); E, puparium; F, adult. (From Fulton, 1953.)

Fig. 191. Sawtoothed grain beetle, Oryzaephilus surinamensis.

Fig. 192. Head and thorax of Oryzaephilus mercator (left) and Oryzaephilus surinamensis, showing difference in lengths of temple regions (seen directly behind the eye). (Courtesy H. E. Hinton.)

Fig. 193. Cigarette beetle, Lasioderma serricorne (left), and drugstore beetle, Stegobium paniceum.

Fig. 194. Damage by cigarette beetles to a can of yeast (left) and to cigars.

Fig. 195. Pineapple beetle, Carpophilus humeralis.

Fig. 196. Codling moth, Laspeyresia pomonella. Top, female; bottam overwintering larva in a silken cocoon.

Fig. 197. Filbertworm, Melissopus latiferreanus. (Top), male (above); female (below). Bottom, larva infesting a walnut. (Courtesy Oscar Bacon.)

Fig. 198. Navel orangeworm, Paramyelois transitella. Top, adult; bottom, larvae in a walnut.

Fig. 199. Mite pests of stored products. Grain mite, Acarus siro (left), and grocer's itch mite, Glycyphagus domesticus. (From A. M. Hughes, 1961.)


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