Walter Ebeling

Chapter 9, part 4
Pests Attacking Man and His Pets

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There are several groups of arthropods that do not envenomate their victims, but become pests by merely being present in homes or other locations inhabited by man and his domestic animals. Some species, such as certain midges, become so pestiferous that they may cause recreational areas to be abandoned, or may deface lakeshore property. Others, such as the eye gnats, not only annoy the residents of an infested area, but interfere with the harvesting of crops. Such species are discussed in the present section, along with the larvae of certain insects that invade body tissues or cavities of humans, causing a condition known as myiasis, which is discussed near the end of the section.

Phantom Midges (Subfamily Chaoborinae)

Some authors consider these midges to be members of a distinct family of Diptera, and give them the common name, "chaoborid gnats," from the family name, Chaoboridae. In this book, they are considered to a be a subfamily of the Culicidae, along with the dixine midges (Dixinae) and the mosquitoes (Culicinae). (The mosquitoes are by far the most important culicid subfamily, and are practically the only species with mouthparts that can pierce the skin and suck blood.)

Description and Biology. The adult phantom midges are somewhat similar to mosquitoes, but lack the long proboscis and do not bite. Their mouthparts are no longer than their heads. The wing scales so characteristic of Culicinae are present only in the hind margins of the wings of the Chaoborinae; there are few or no scales along the veins. The larvae of some phantom midges resemble certain mosquito larvae so closely, that the two might be confused by the casual observer. However, the larvae of phantom midges usually have their antennae inserted near the midline of the head; if inserted elsewhere, the antennae are provided with prehensile hairs with which the larvae can seize aquatic prey. Mosquito larvae always have their antennae inserted laterally on the head.

The term "phantom" is descriptive of the larvae, which are almost transparent and are difficult to see, even in clear water. Their antennae extend downward, and have 3 to 5 apical bristles that aid in securing food and in locomotion. The mouth has a large, eversible pharyngeal sac that functions as a crop for the selection of food and the rejection of extraneous materials. The pupae somewhat resemble those of mosquitoes. They have a large cephalothoracic area, bladderlike respiratory tubes, and 2 wide, flat, anal paddles. The dark, spindleshaped eggs float singly or in small rafts on the surface of the water, but those of some species soon sink to the bottom.

Clear Lake gnat, Chaoborus astictopus Dyar and Shannon (= lacustris Freeborn)

This species first came to attention in the Clear Lake area in northern California. The gnats appear early in May and may be found until about mid-October. In the days before effective control, they were so extremely abundant that they got into the eyes, mouths, noses, and ears of the lakeshore residents, and often became so thick on door and window screens that scarcely any light could penetrate (Herms, 1937). At one time, this gnat was a serious problem only near Clear Lake, but as the water resources of the state continue to be developed, the problem is becoming widespread - the insects are becoming as numerous in many dams, reservoirs, and smaller ponds in other parts of California as they originally were in Clear Lake. The species is very adaptable to varied water conditions (Cook, 1967). Chaoborus punctipennis (Say), a species of similar appearance and habits, is a pest in Florida and along the Atlantic seacoast.

Description. The adults of C. astictopus are brown, with a vestiture of straw-colored hairs. They are 4 to 5 mm long. The males have a longer and more slender abdomen than the females and, as in the case of the mosquitoes, have more plumose antennae; they also have a pair of claspers at the tip of the abdomen (figure 314, A).

Biology. The females lay their dark, spindleshaped eggs (figure 314, D) on the surface of the water, where they form geometrical designs similar to those of anopheline mosquitoes. Unlike mosquito eggs, however, they sink to the bottom when the water is slightly agitated. They hatch in 20 to 24 hours. When full grown, the "phantom larvae" (figure 314, E) are 8 to 10 mm long. They do not have to come to the surface for air as mosquito larvae do, for they breathe by means of gills, and possibly cutaneously as well. There are 4 larval instars (Herms, 1937). The first-, second-, and some of the third-instar larvae are free-swimming, and most of the third and all of the fourth and pupal instars stay in the bottom mud (Snell and Hazeltine, 1963). In laboratory experiments at 70 to 80°F (21 -to 27 °C) and with abundant plankton available, the larvae could mature in 11 to 25 days, although sometimes the fourth instar was greatly prolonged. Mature larvae fed readily upon small mosquito larvae that were offered to them. The pupal stage was 2 to 3 days. The adults freed themselves from the pupal skins in a few seconds, and were able to fly almost immediately. The emerging adults flew to shore, where they mated in shoreline trees (Deonier, 1943).

Snell and Hazeltine (1963) treated the water of a pond with methyl parathion at 4 ppb (parts per billion), which had a residual effect lasting only 9 days and killed only the first- and second-instar larvae and most of the third-instar larvae. By this treatment, an overlapping of instars and stages was eliminated sufficiently to enable them to measure the developmental periods by periodic samplings of the water. Under the natural ambient conditions of the pond, the period required for each stage and instar was found to be as follows: egg, 1 day; first instar larva, 5-6 days; second instar larva, 5-6 days; third instar larva, 10-11 days; fourth instar larva, 11-19 days; pupa, 2-3 days; adult preoviposition period, 2 days; resulting in 36 to 48 days for a summer generation.

Control. The chlorinated hydrocarbon TDE, in applications of up to 20 ppb in a single late. season treatment of the entire lake, resulted in effective phantom midge control for a 2-year period in Clear Lake in 1949. The lake was treated again in 1954 and 1957. The control was less effective with each treatment, that of 1957 giving only 95% control. Great concentrations of insecticide were found in fish, and large numbers of birds that nested around Clear Lake were killed. The decision was made to change to a rapidly biodegradable organophosphorus insecticide. In 1962 3 treatments with an acetone solution of methyl parathion, the first with 2.2 ppb and the second and third with 3.3 ppb, resulted in control of the gnats with no ill effects on wildlife (Hazeltine, 1962; 1963). Currently, methyl parathion is being applied in 3 treatments, approximately 3 weeks apart, in July and August, standardizing concentration at 3 ppb. This has broken the cycle of the Clear Lake gnat without measurable harm to the lake's overall biology.

Midges (Chironomidae)

This is a family of minute to moderately large species, the adults of which superficially resemble mosquitoes. The smaller species are believed by some people to be "young" mosquitoes. However, midges differ from mosquitoes in that the wings are not scaled and the mouthparts are short and not adapted for biting. Adult midges are slender, seldom more than 10 mm long, but usually less than 5 mm; the thorax is relatively large, partially concealing the small, spherical head; and the antennae are slender, 5- to 14-segmented, more or less hairy in the females but plumose in the males. The legs are slender and long, especially the forelegs, and the tarsi are often very long. The wings are long and narrow, bare or sparsely haired in the females and plumose in the males. The abdomen is long and narrow, especially in the males, that of the females being shorter, and more robust, and the mouthparts form a short proboscis.

Grodhaus (1963) described in concise tabular form the adults of 13 chironomid species considered to be important as nuisance pests in California, giving color, wing length, larval habits associated with mass emergences, notes on geographic occurrences in California, and the characteristics of the 3 subfamilies. A key to chironomid adults taken in or near rice fields, and keys to the species of those larvae and pupae that were reared to adults, were, prepared by Darby (1962). Keys to the adults and larvae of California lagoon-inhabiting species were prepared by Grodhaus (1967) but care should be taken when identifying adults with these keys not to include species from sources other than lagoons.

Similarly to mosquitoes, midges oviposit on water. The midge larvae are scavengers, and are aquatic or rarely terrestrial. Terrestrial species live in and on decayed vegetation, dung, fungi, mosses, under bark,,and in the soil. Aquatic larvae are found in quiet or flowing water, and may become abundant in lakes, ponds, reservoirs, and tanks. Most are bottom-feeders, and are sometimes found at depths of nearly 1,000 ft (300 m). For most species,,the food is thought to be particulate matter consisting of algae, other plant cells, and miscellaneous detritus. They possess a closed (apneustic) respiratory system and, unlike mosquito larvae, need not come to the surface for air. They absorb oxygen dissolved in the water by means of small "gills." Some larvae are freeliving, and others make mud tubes or cases on stones, leaves, and pieces of wood.

In the subfamily Chironominae, which includes the important genus Chironomus, the larvae are usually red, with some variation in intensity. They typically inhabit tubes constructed of small particles and located in the bottom sediment. The pupae also inhabit these tubes, leaving just before adult emergence (Grodhaus, 1963).

Chironomid Midges as Pests. Despite not being able to pierce the skin or bite, midges can nevertheless be serious nuisances in urban as well as rural areas. In urban areas, runoff water from the streets of residential and commercial areas finds its way into a network of drainage ditches and flood channels. The drainage water is high in nutrients and creates a very favorable environment for midge production throughout the year except, in California, during the winter floods. Immediately following the winter floods, species of Chironomus and Tanypus can become so numerous that thousands will rest on the outside walls, under the eaves, and in doorways of houses within a quarter mile (400 m) of the breeding sources, and will enter the home through the slightest crack or opening. This is especially the case at night, for they are attracted to artificial light (Thompson et al., 1970). They fly into people's eyes, ears, and mouths, and are sometimes inhaled. When in large numbers, they soon contaminate food served in illuminated areas. Where outbreaks are frequent, spiders that feed on midges soon become nuisances also. Real estate values tend to be reduced where midges are abundant. Midges also can interfere with the processing of paper, plastics, and food products, and with automotive refinishing operations (Grodhaus, 1963; Anderson et al., 1965).

Chironomids often occur in large numbers in reservoirs, and may be passed into the drinking water. They often emerge in extremely large numbers from waste-water stabilization lagoons or oxidation ponds (Usinger and Kellen, 1955; Grodhaus, 1967; Brumbaugh et al., 1969). These are shallow impoundments receiving domestic sewage or other liquid waste. Bacterial action and photosynthesis alter the organic material, and much of the waste is converted into plankton. The soft layer of organic sediment that accumulates on the bottom provides food and substrate for chironomid larvae. As might be expected, chironomid midges are produced in enormous numbers in rice fields. Darby (1962) recorded 30 species from rice fields of the southern Sacramento Valley, California, 18 of which were considered to be rare.

Chironomus plumosus L.

These midges, often called "lake flies," are common over much of the United States. They can create a serious problem in lakefront communities. The problem in one such community in California was graphically described by Bay (1967). Chironomus plumosus is a pest not only because of the presence of bothersome swarms of adults, but also because the adults may lay their eggs in large, dark, sticky deposits glued to the sides of buildings (figure 315) and to surfaces such as windows, walls, neon signs, and moored boats. These exposed egg masses, each containing up to 2,000 eggs, never hatch, for hatching is possible only when they are deposited in water. The egg masses either become hard and dry or, if they become wet, dissolve and smear inio unsightly brown stains. If there are no lights on shore during the hour following sunset, few egg masses will be deposited on terrestrial structures, but if the females are attracted by shore lights, they will remain and deposit their eggs there, dying afterward. The dry egg masses can be removed by wiping with a dry cloth. If the eggs have been smeared by rain, they should be wet with a 10 to 20% aqueous solution of Clorox or a similar commercial bleach, then washed away after a few minutes (Bay, 1967).

Description. The adults (figure 316) are about 12 mm long - the largest American chironomids. They are predominantly light brown, often tinged with green or yellow, and with the basal two-thirds of each abdominal segment dark brown. The thoracic tergites have median anterior and lateral posterior dark areas. The pale legs have narrow, dark bands at the distal end of each tarsal segment. When it first emerges, the adult has a reddish cast, but this disappears and darkens after a few hours, although some of the reddish color may be visible in the thorax for more than a day (Hilsenhoff, 1966).

Life Cycle. More than 90% of the oviposition occurs within 1 or 2 hours after sundown. The egg mass, 3 to 5 mm long, is ordinarily placed on a lake or other large body of water, where it swells to several times its original size and becomes transparent, revealing the individual eggs (figure 317). The egg mass slowly sinks to the bottom (Hilsenhoff, 1966; Bay, 1967). The time required for the eggs to hatch depends on the temperature at the bottom, and can vary from 3 days at 24 °C (75 °F) to 14 at 9 °C (48 °F) (Hilsenhoff, 1966).

The first-instar larvae are colorless, and not until late in the second instar does a pale-pink color appear. In the third instar, the color deepens to light red, becoming very deep red in the fourth instar. There is also considerable green pigment just before pupation, especially in the thoracic region. Full-grown larvae range from 15 to 30 mm in length. The larvae feed on decayed algae and diatoms. At least the last 3 instars, they construct U-shaped tubes in the mud. Fourth-instar larvae were observed to crawl from their tubes to feed while remaining anchored to the tubes by their caudal prolegs. Whereas the tubes of the second and third-instar larvae are at or just beneath the mud surface, the fourth-instar larvae may construct their U-shaped tubes to extend as far as 8 cm into the mud.

Pupation takes place in the larval burrow. In Lake Winnebago, Wisconsin, pupation may require 6 to 10 days in early May, when mud temperatures at the bottom are about 10 °C (50 °F), and as little as 1 day in July and August, when the temperatures normally range from 23 to 25 °C (73 to 77°F). As with the larvae, the pupa is also red, with some green pigment, and as it ages it becomes darker until it is almost black. Female pupae average 17.7 mm in length, compared with 16.8 mm for the males. After pupation is complete, the pupa leaves the larval burrow and swims to the surface. The adult then emerges in 15 to 30 seconds. The empty pupal cases float for at least 24 hours, and often accumulate in windrows on the surface (Hilsenhoff, 1966).

Chironomus attenuatus Walker [=Tendipes decorus Johannsen and T. attenuatus (Walker)]

This species is widely distributed in the United States, and is often a troublesome pest. It normally breeds in lakes, ponds, rivers, and streams, but in semi-arid regions, seasonal breeding situations can be developed. In California, under favorable rainfall and water conditions, it may develop 2 or more consecutive broods in the organic ooze of its aquatic habitats, with larval populations of 5,000 to 50,000 per square meter. The swarms of adults may interfere not only with normal outdoor activity, such as clothes drying and painting, but may enter houses and annoy the occupants, or enter lighted commercial buildings and cause damage, such as becoming embedded in plastic sheeting or bringing the enameling of cars to a halt (Grant 1960). Along with other chironomids, particularly Tanypus grodhausi, it can be a hazard to motorists when occurring in dense swarms near breeding sites (Bay et al., 1965).

Chironomus attenuatus was among the 3 most important species of related midges in Los Angeles County's water-spreading basins surveyed by Anderson et al. (1964), the others being C. californicus and Pentaneura monilis. It was the most important chironomid pest in the waste-water stabilization lagoons at Stockton, California (Brumbaugh et al., 1969), and was one of the few related species found in the organic material of sewage oxidation ponds (Usinger and Kellen, 1955). It was noted to occur in large numbers in California rice fields (Darby, 1962).

Description. The adults (figure 318), are 5 to 6.5 mm long, and have a ground color of light pruinose green to light brown. The antennae, mouthparts, and thoracic markings are brownish ochraceous to dark brown. The abdomen is usually pale green, with tergites 2 to 7 each having a central transverse brown band, indicated in the figure, occupying from a fourth to most of its length. In occasional specimens, the abdomen is entirely green. The males may be identified by their plumose antennae; otherwise, the 2 sexes are similar in general appearance. The usual absence of a "tarsal beard" and the heavy, dark-brown wing veins distinguish this exceptionally variable species from others in the genus.

Biology. From the time a swarm of adults is noticed at sunset, it grows in size until it may form a column 30 cm in diameter, about 1.5 m in height, and with a base about that distance above the ground. Mating takes place in the swarm. When ovipositing, the female extrudes a brown egg mass and deposits it on the hind femora. It is held there for 2 or 3 minutes, then thrown down on a water surface. The egg mass then gradually expands. There is an average of about 700 eggs in the cluster (Ping, 1917).

The larva, at first pale gray, becomes red, with a brownish head, and is about 5 mm long. In every respect it resembles the mature larva, which attains a length of 11 to 12 mm and has ventral blood gills about 2 mm long. The 1arva has been reported to feed on aquatic vegetation (Ping, 1917), but it has also been shown that the introduction of raw organic matter, when it overbalances the established agents of decomposition, tends to support high populations of this and other midges (Whitsel et al., 1963).

The mature pupa, about 7 mm long, swims tadpolelike under the surface of the water. After pupation is complete, the pupa leaves the larval burrow and swims to the surface. The adult usually frees itself from the pupal skin in less than 15 seconds, and frequently within 4 or 5 seconds. Adults have lived for as long as 6 days under very humid laboratory conditions, but might live longer in the grasses, rushes, and sedges on the shores of bodies of water. There are usually 5 generations per year (Ping, 1917; Hilsenhoff, 1966).

Chironomus californicus Johannsen (=Dicrotendipes)

Large numbers of these midges (figure 319) become nuisances when they rest on vegetation and screen doors in residential properties near reservoirs and other sources. The adults are grayish in color and about 4.5 mm long, apparently too large to pass through ordinary fly screen. According to E. C. Bay (correspondence), peak emergences usually occur between 2 and 3 weeks after newly wetted environments are formed, then decline to about 10 or 15% of their original numbers after the initial outbreak. The drying and rewetting of reservoirs, or large parts thereof, may result in additional outbreaks. Practically all mature (nonteneral) pupae within a pond transform and emerge in an evening, predominantly in a 30- to 60-minute period shortly after sundown. This is also about the time of maximum egg deposition (Frommer and Rauch, 1971).

Control of Chironomid Midges

The midges have been controlled for relatively brief periods by fogging with malathion in fuel oil at 0.5 lb (0.23 kg) of toxicant per acre (0.405 ha), or by applying fenthion in a granular formulation at 0.2 lb (0.09 kg) per acre (Hagmann, 1963; Patterson and Wilson, 1966). Tests in a shallow sewage oxidation pond showed chlorpyrifos, parathion, and methyl parathion to be effective at 0.2 to 0.25 lb (0.09 to 0. 11 kg) per acre against Goeldichironomus holoprassinus (Rempel), Tanypus grodhausi (Sublette), and Chironomus sp. 51 (Mulla and Khasawinah, 1969). Chironomid larvae have been controlled in waste-water stabilization lagoons with a specially designed, quickbreaking emulsion of fenthion and methyl parathion (Brumbaugh et al., 1969). Chlorpyrifos, applied as granules or emulsifiable concentrate at 0.2 lb per acre, gave excellent control of chironomid midge larvae in lakes. The concentrate caused slight kills of certain species of fish, but the granular formulation did not (Mulla et al., 1971). Granular formulations have the advantage of being selective, for they quickly sink to the bottom where the larvae live, and are therefore less likely to kill nontarget species (Jamnback, 1969). A fog of base oil containing 5% malathion and applied with a portable fog generator is effective in eliminating adult midges from shrubbery, lawns, and the walls of residences, but only for a few hours.

Chironomid midges are rarely nuisances in a well-balanced aquatic community. Pollution of water with materials that encourage the growth of the algae upon which the midge larvae feed results in excessive midge populations. One of the disadvantages of insecticides is that they kill the larvae without destroying, the algae. The food supply thus accumulates, and favors an outbreak of midges when the insecticide is no longer effective and the body of water is recolonized (Jamnback, 1969). The midges have been controlled in small bodies of water by stocking them with carp and goldfish at the rate of 150 to 500 lb per acre (68 to 225 kg per 0.405 ha) of water surface (Bay and Andemn, 1965).

Moth Flies and Allies (Psychodidae)

The psychodids are small, long-legged, hairy, mothlike Diptera (figure 319A). They are rarely more than 5 mm long. These flies are found in moist places, sometimes in such numbers that it is difficult to avoid inhaling them. This is especially true of some species that breed in sewage filter plants, where they are called "filter flies" or "sewage flies." Swarms of these flies, in the genera Psychoda and Telmatoscopus, may also emerge from sink and bathtub drains. The species of Psychoda have the terminal segments of their antennae reduced in size, whereas those of Telmatoscopus do not (figure 319 A). Although the moth flies have been considered only as annoyances in the United States, in South Africa they have been implicated in many cases of inhalant allergy.

Most species of moth flies are in the subfamily Psychodinae. Their wings are usually held rooflike over the body. Their mouthparts are short and are not adapted for bloodsucking. They may be found in shady places, along streams with decaying wastes, or around sap exuding from trees. Large numbers may be seen on dense foliage in swamps, crawling about on the undersurfaces of leaves. Except under artificial conditions, they are of little importance as pests. The eggs of this subfamily are pale or brown, oval, and have inconspicuous reticulations. The larvae are commonly aquatic. They are elongate and cylindrical, but are flattened ventrally and have 8 ventral suckers. The tergal plates and the posterior siphon and spiracle are conspicuous features.

Species in the subfamily Phlebotominae, the "sand flies," are less hairy than the Psychodinae, their wings are not held rooflike over the body, and the larvae are never truly aquatic. The females have rather long, piercing mouthparts, adapted for bloodsucking. The males suck moisture from any available source, such as perspiration from humans. These gnats are active only at night and when there is little or no wind. During the day, they may be found in sheltered places both outdoors and in buildings. There is only 1 genus, Phlebotomus, species of which are carriers of diseases such as pappataci fever, kala azar, leishmaniasis, and Oroya fever in many tropical areas of the world, but this does not occur in the United States.

Moth Flies in Sewage Filter Plants

Moth flies may develop in the muck or gelatinous material that accumulates in sewage disposal beds, septic tanks, compost, or dirty garbage containers, or they may emerge from the drains of sinks or bathtubs, from treeholes, rain barrels, or from very moist organic solids and bird nests that have accumulations of moist excreta. They are probably most commonly associated with filter sewage beds where the larvae and pupae thrive in the gelatinous film covering the filter stones or in other places where decomposing organic materials are found. The larvae are beneficial in that they feed on algae, fungi, bacteria, and sludge in sewage-disposal beds, breaking down the gelatinous film into small fecal pellets that are easily washed away. Moth flies are pests when the adult flies become so abundant that they get into the eyes, ears, and noses of the workmen in the area. They may also find their way into nearby homes, or may even originate in drain pipes within the homes.

Psychodids go through their life cycles in 1 to 3 weeks, and live about 2 weeks after emerging. They are weak fliers, so that in the home they are generally seen crawling on walls or other surfaces. When they do fly, their flight is in short, jerky lines and for only a few feet at a time. They are attracted to lights, and are so small that they can penetrate ordinary fly screens.

Pacific drain fly, Psychoda phalenoides (L.) (= pacifica Kincaid)

This is the psychodid most commonly referred to as a pest along the Pacific Coast, ranging from Alaska to southern California. The adult is 2 to 2.3 mm long, with brownish-gray wings and with body and wings densely covered with long hairs. As with most other psychodids, the wings are usually borne rooflike over the body, and each segment of the 13-segmented antennae has a bulbous swelling with a whorl of long hairs. Larvae and pupae of the Pacific drain fly may occur in the gelatinous lining of the portion of a drain pipe beneath a sink that is above the permanently waterfilled trap. In one experiment, when the gelatinous material was removed by forcng a paper swab with an outer coating of wax paper down the drain, no more flies emerged from the sink (Mallis and Pence, 1941).

Psychoda alternata Say

This species is 2 mm long, and has 15-segmented antennae. It ranges from Florida to Massachusetts and westward to Washington and California. The female lays a gelatinous mass of 20 to 100 eggs in any of the suitable breeding media just described. The eggs hatch in 32 to 48 hours, larval development requires 9 to 15 days, and the pupal period lasts 20 to 40 hours. The life cycle takes 21 to 27 days under room conditions. The adults are weak fliers, and can often be found resting on foliage. They seek shade in the daytime, but are attracted to light at night. They feed on nectar or polluted water. They may enter houses in large numbers (Quate, 1955; Scott, 1961c).

Other Species of Psychoda Also common in sewage filter beds are 2 species that are pale yellowish and, as with all species of Psychoda, the terminal segments of the antennae are reduced in size. Psychoda satchelli Quate has 14-segmented antennae. It ranges from Georgia to Quebec and westward to Alaska and California. Psychoda cinerea Banks has 16-segmented antennae. Unlike other species with 16-segmented antennae, the 3 terminal segments are separate and are equal in size. It ranges from Puerto Rico to Ontario and westward to Washington and California (Quate, 1955).

Telmatoscopus albipunctatus (Williston)

This is one of the moth flies that infests sewage filter beds and drain pipes (figure 319 A, bottom). It is widely distributed over the United States. The specimen shown in the figure was one of many that emerged from the drain pipe of an infrequently used sink, with a leaking faucet, in a glasshouse on our Los Angeles campus. Its color is generally brown or blackish, but with the white hairs on its thorax and antennae rather conspicuous. These features, along with the white spots at the tips of the wing veins, clearly seen in the figure, make this a well-marked species that is easily distinguished from other North American species of the genus (Quate, 1955).

The larva is 8 to 10 mm long. It has 26 tergal plates: 2 on segments 1 to 4 and 3 on segments 5 to 10 (Quate, 1955). Its brown or blackish color distinguishes it from the pale-yellowish color of the Psychoda species. (Scott, 1961c). Besides being found in sinks and drains, the larvae have been found in mud, in water in treeholes and rain barrels, in shallow pools partly filled with dead leaves and debris, and in the rinds of kukui tree fruit (Aleurites moluccana Willdenow; candlenut; Euphorbiaceae) (Williams, 1943).

Allergic Reactions to Moth Flies Thirteen cases of bronchial asthma were reported among workers at a sewage plant in the Transvaal, South Africa, all the result of allergic response to the moth fly Psychoda alternata. The inhalant allergen was demonstrated to be the dust resulting from the disintegration of the flies' bodies. One individual who was investigated with particular thoroughness was found to have no family history of allergy, and was not found to be sensitive to any of the more common causes of allergy, such as feathers, dusts, and pollens (Ordman, 1946).

Control of Moth Flies in Sewage Filter Beds

In sewage filters, flooding and treatment of the slime layer result in good control of moth flies. However, the efficiency of the biofilter depends on the activity of this slime layer, and it must not be destroyed. Treating the slime with insecticides disrupts its biological equilibrium by killing large numbers of key organisms, and the toxicant may poison aquatic life downstream from the filter bed. Scott (1961c) suggested that weeds and grass be mowed short throughout the sewage plant area, and that walls and other structural elements of the filters be sprayed with 2.5% malathion suspension at 1 gal per 1,000 sq ft (4 L per 93 sq m), using a flat-spray nozzle, to give a residual deposit. He suggested that the spray treatment extend out from the edge of the filter for 20 ft (6 m), but that the slime layer not be sprayed. If necessary, the edges and walls of sludge-drying beds could be sprayed, and steps to improve the quality of the product coming from digestors should be taken. The treatment should be repeated as needed, typically at 2-month intervals. Scott recommended DDT for the treatment of sludge beds, but DDT, aldrin, and dieldrin are no longer registered for such uses as the control of filter fly larvae in sewage systems or the control of mosquito or tabanid larvae in aquatic outdoor areas (Anonymous, 1970a). The appropriate state authorities should be consulted for information on effective, currently registered insecticides. Scott also noted that the removal of vegetation reduced favored resting sites for filter fly adults, and that residual insecticides killed adult flies so rapidly that large populations could not build up. Some larvae might remain in the filter beds, and occasionally small "blooms" of adults might occur, but they usually persisted in such small numbers that they were no longer pests.

Frit Flies and Eye Gnats (Chloropidae)

The frit flies are very small insects, rarely exceeding 3 mm in length. They are very common, and may be collected almost anywhere on many plants and particularly on grasses, on which the larvae feed. Many species are pests on cereal plants all over the world, the wheat stem maggot, Meromyza americana Fitch, the frit fly, Oscinella frit (L.), and the American frit fly, 0. soror (Macquart), being the principal species in the United States (Schread, 1964). Two species, 0. neocoxendix Sabrosky and 0. coxendix (Fitch), cause "silver top" of bluegrass (Poa pratensis) (Starks and Thurston, 1962).

The eye gnats (Hippelates spp.) are strikingly different from other chloropids in habits and in the manner in which they are pests. In California, they occur south of Madera County at lower elevations; the species are H. collusor (Townsend), dorsalis Loew, impressus Becker, pusio Loew, robertsoni Sabrosky, and hermsi Sabrosky. All except H. hermsi are pests (Ecke, 1963). Herms (1928) pointed out that H. collusor was probably responsible for the epidemics of bacterial conjunctivitis (pinkeye) in the Coachella Valley in southern California, and a few years later the same species was incriminated as the vector of the disease in Florida (Bengston, 1933). Eye gnats later created problems in other cultivated areas, such as the Imperial and San Joaquin valleys. They are present in many desert areas of California, such as the Mojave Desert (Womeldorf and Mortenson, 1963), and could create problems if and when such areas were intensively cultivated and irrigated.

Some gnat-producing areas are adjacent to residential tracts, but many are 1 to 5 mi (1.6 to 8 km) from them. By means of gnats tagged with radioactive phosphorus, it was shown that H. collusor could disperse both upwind and downwind, with the greatest distances traveled in 2 experiments being 4.1 and 4.3 mi (6.6 and 6.9 km), respectively, in the direction of the wind (Mulla and March, 1959).

Hippelates impressus, first collected in California in 1963, has been reported from near sea level to 6,000 ft (1,800 m) elevation in large areas of southeastern California, and occurs in border states east to Texas, as well as in Mexico and the Virgin Islands. It is highly pestiferous in foothill and mountain habitats. Among eye gnats in California, it is exceeded in importance only by H. collusor and H. dorsalis. Nothing is known about the biology and breeding habits of H. impressus, but heavy summer rains, which may occur in the mountains despite the seasonal aridity of the general desert region, seem to cause outbreaks of this eye gnat (Mulla, 1971).

Description of Stages. Adult eye gnats are 1.5 to 2.5 mm long. Most species range from shiny black to dull gray, with yellow, orange, or darkbrown and orange legs (plate VIII, 3; figure 320). Hippelates impressus is a small, reddish-orange species. Most Hippelates eye gnats have a large, black, curved spur on the hind tibia. They can also be distinguished from other small flies by their small mouthparts and short antennae with rounded third segments and bare aristae.

The eggs are 0.45 to 0.52 mm long, at first pearly white or translucent, but becoming snowy white as they mature. They are fluted lengthwise, distinctly curved, and bluntly tapered at either end. The larvae have the typical maggotlike form, and are 2.5 to 3.5 mm long when full grown. Hall (1932) found that the females would oviposit upon various kinds of excrement and decaying meats, fruits, and other vegetable matter. He did not determine the number of eggs a single female could deposit, but found an average of 24 fully formed eggs in gravid females, as well as developing eggs in the "ovarian spaces." Under moist conditions in the insectary, the average incubation period was 3.7 days. Later investigations showed that H. collusor oviposited in soil that contained minimum levels of moisture adequate for egg hatching and subsequent larval development (Legner and Bay, 1965; Legner, 1968). Recently cultivated soil or emergent vegetation stimulated oviposition. The eggs were generally "ejected with propulsion" to depths averaging less than 5 mm below the soil surface.

Hall (1932) observed that the larvae burrowed into a food medium or surrounding sand as soon as they emerged from the eggs. If the medium was sufficiently moist, the larvae came to the surface, and as the moisture decreased, they retreated to their tunnels in the soil. Their resistance to desiccation increased with increasing age. The larval period ranged from 5 to 46 days, depending on food medium, moisture, and temperature. On human excrement, it averaged 11.4 days; on canine excrement, 8.7 days; and on decaying oranges, 17 days. Hall also determined that H. collusor (figure 320), under insectary conditions, could complete its development from egg to adult in 11 days. The longest period was slightly more than 3 months and the average period was 18.5 days. Herms and Burgess (1930) determined that in the laboratory at temperatures ranging from 80 to 105 °F (27 to 41 °C), the life cycle required an average of about 3 weeks. Much more information was obtained by workers in later years on the biology of eye gnats under field conditions.

After emerging from eggs in the soil, the larvae of H. collusor move to greater depths and feed on the living roots of plants and on dead organic matter that has been made available through water saturation (Legner et al., 1966; Legner and Olton, 1969). Pupae are usually found in the larval tunnels, either in the food medium or in surrounding sand. After the adult emerges from the puparium, it digs through several centimeters of soil to reach the surface, where it inflates its wings (Legner et al., 1971).

Habitat. Hippelates larvae feed on decaying organic matter in soil. It is necessary that the soil be friable, tilled, and with adequate moisture in order to support heavy populations of gnats (Mulla, 1963c). Most of the eggs are laid within a few hours after the land has been plowed (Bigham, 1941; Mulla, 1966). Eye gnats probably were not a problem until agricultural operations were begun. Some species of eye gnats breed in limited numbers in alfalfa fields, golf courses, lawns, ditch banks, river basins and banks, and lake shores, but tilled farm lands produce by far the greatest number. However, this is the case only when organic matter is worked into the soil.

Injury Caused by Eye Gnats. Eye gnats are attracted to wounds, scabs, pus, blood, sebaceous material, the natural orifices of the body, and especially to the eyes. They do not bite; in fact, they have sponging mouthparts similar to those of the house fly. They feed by everting the soft, pseudotracheate labellum over moist surfaces and then sucking in liquids. The labellum has spines that produce many minute scratches on the eyeball while the insect is feeding, assisting the entry of pathogenic organisms, and resulting in the malady known as "pinkeye." Even if they were not vectors of pinkeye, the gnats would be very annoying.

Repellents. Chemical repellents for eye gnats were investigated by Mulla (1963b), using an olfactometer and skin tests. In the skin tests, 2.5 ml of each repellent solution were rubbed evenly on the face, ears, back of the neck, and on the arms of each of 3 or 4 different people on different occasions. Tryile Mix (dimethyl phthalate 64%, ethyl hexanediol 17%, Indalone 19%), ethyl hexanediol, and dimethyl carbate performed best in both the olfactometer and the skin tests.

Control. Control has so far been based principally on certain cultural measures. In experiments made in a date garden in the Coachella Valley in southern California, Mulla (1963c) found that when weeds were controlled by the use of herbicides, gnat control was very good. Herbicides were found to be superior to frequent tillage in controlling weeds and suppressin gnat breeding. Petroleum oils applied to weeds and cover crops up to 9 days before disking the ground resulted in excellent control of H. collusor, as well as H. dorsalis and other eye gnats of less importance in experiments made in the Coachella Valley. This was probably because the oil caused vegetation to be unfit for food for the larvae after it had been disked into the soil. Certain components of the oils might also have acted as repellents against ovipositing eye gnats or as ovicides or larvicides, even after they had been disked in (Mulla et al., 1966). However, oil treatments applied immediately after disking also resulted in good control. This was probably because the gnats tended to increase oviposition activity after disturbance or disking of their natural breeding habitats. Most of this oviposition took place within 24 hours, and oil applied immediately after disking probably repelled the ovipositing insects. Peak emergence of eye gnats and the duration of the emergence period were influenced by weather, but in the Coachella Valley, most of the emergence took place within 2 to 4 weeks after disking (Mulla, 1966). (Where vegetation is controlled by a herbicide, as in "clean culture" of citrus orchards, disking does not affect eye gnat breeding, for no eye gnats are present.)

The effect of disturbance of the soil on the eye gnat population was again demonstrated in South Carolina, when plots of fairly high grass 100 x 100 ft (30 x 30 m) in area were either plowed under or left undisturbed. Emergence traps placed in the plots at intervals between the eighteenth and thirty-third day after plowing showed striking differences in the catches of flies in the plowed and unplowed plots. Of the 4 species involved H. pusio; a variant of H. pusio; H. bishoppi Sabrosky; and H. dissidens (Tucker) the lastnamed, a relatively unimportant species, was the only one not significantly affected by plowing (Gaydon and Adkins, 1969).

Natural Enemies. Legner et al. (1971) considered the natural enemies of Hippelates collusor to be of sufficient importance to justify consideration of "integrated control" (see that heading in chapter 2). The whole community of predators and parasites, as well as nonpredatory species, should be taken into consideration, for the latter can be regarded as potential competitors of eye gnats for food and space. Reductions of field populations of H. collusor, as well as of the biting midge Leptoconops kerteszi, were obtained with granular and spray applications of urea to the soil. The possibility of reducing the breeding potential of pestiferous soil arthropods by this method without creating problems of resistance and destruction of natural enemies was indicated by Legner et al. (1970). More natural enemies have since been introduced, but they are helpful only under conditions in which the soil is not disturbed by cultivation (Legner and Bay, 1970).

Other Chloropids

These insects are sometimes so numerous in buildings in Europe that they cover ceilings and windows and make some rooms uninhabitable. The principal pest is Thaumatomyia notata Meigen (= Chloropisca). Therefore, it is of interest that a closely related species, T. annulata (Walker), was found by Sabrosky (1940) in great numbers around window casings of a hotel in Michigan, appearing year after year. These gnats were said to be easily controlled with pyrethrum sprays or dusts. C. W. Sabrosky (correspondence) has since received reports of this species in houses, sometimes in large numbers, in areas ranging from Idaho to New Hampshire. One correspondent from Montreal, Wisconsin, stated that the flies were nuisances in the homes throughout his immediate neighborhood.

stable fly, Stomoxys calcitrans (L.) (Muscidae)

The stable fly (figure 160, B, chapter 6) is often mistaken for the house fly. Distinguishing features and biology are discussed in that chapter. The house fly and the stable fly may be found together in houses, but the latter is primarily an outdoor, day-biting fly that is most likely to be found indoors in the fall and during rainy weather. Unlike the house fly, it has a stiff proboscis (figure 46, G, chapter 4), with which it can inflict a painful bite even through socks or stockings, pierce the skin, and draw blood. The small labella at the tip of the proboscis are everted, exposing on their inner surfaces a set of filelike teeth with which the fly rasps a way through the skin. A rapid twisting of the labella aids in the cutting, and the slender anterior part of the labium is soon completely inserted. If the fly is left undisturbed, it may feed for as long as 15 minutes and consume about 25 mg of blood-about 3 times its own weight. Thus, the stable fly takes much bigger meals than the house fly, does not have to seek food continuously, and spends more time resting than the house fly. Both sexes bite and suck blood, and attack domestic animals and man. The stable fly is often found on piles of seaweed on beaches and along the vegetation-strewn shores of lakes, particularly where wet plant debris has accumulated in compost mounds, and can be a great annoyance in recreation areas. In Florida, the application of 1% methoxychlor emulsion to piles of decaying aquatic vegetation has controlled stable flies for periods of 30 days or longer. Methoxychlor is chemically related to DDT, but has a much lower mammalian toxicity (LD50, 5,000-7,000 mg/kg), and is much more readily biodegradable and less persistent in the environment. The stable fly differs from others discussed in this section of chapter 9 in that it inflicts a painful bite but apparently does not envenomate. It should be able to transmit disease germs, at least mechanically, and has been occasionally incriminated as a carrier of certain ailments to animals, but apparently not to man.

March Flies (Bibionidae)

March flies are small to medium in size, robust, mostly black, dark gray, or reddish brown, and hairy. They have large heads, well-developed mouthparts, and large eyes that are holoptic (contiguous) in the males. The antennae are short, and 8- to 16-segmented. The anterior femora are usually thickened and sometimes greatly swollen. The cylindrical, legless larvae have large heads, and feed on decaying vegetable matter, dung, and especially on the roots of grasses. They pupate in the soil. According to Curran (1965), the common name is derived from the frequent occurrence of Bibio albipennis Say (= hirtus Loew), the most widespread North American species, in large numbers during the month of March. This species is common in California, as well as B. vestitus Walker. The adults of both species feed in great numbers on nectar in the blossoms of fruit trees. Both are small, black and reddish in color, and hairy, with a conspicuous black spot near the middle of the costal margin of the wing (Essig,1926).

The Genus Dilophus

Inquiries are sometimes received concerning small, black flies," identified as Dilophus occipitalis Coquillett, that are attracted to windows in large numbers. These insects are about 3 mm long, and both sexes are black throughout except for the reddish thorax of the female. She has a conspicuous black spot along the foremargin of each wing, and has a smaller head than the male. This species is common in southern California, and may account for some of the infestations of small flies and "gnats" that are called to our attention every spring (Ebeling, 1964a).

Another bibionid that gives rise to occasional calls from homeowners in southern California is D. orbatus Say (figure 321). It is black, robust, very hairy, and about 6 mm long. In one infestation in June, 1964, adults emerged from a lawn in large numbers in the morning and were abundant by 11 o'clock, but had nearly disappeared by 1:30 in the afternoon. They managed to get into the house and garage. An infestation in another residential property was observed in October, at 3 p.m. The flies were clinging in large clumps to blades of grass in,the lawn. In both instances, the lawn had been excessively fertilized with manure and bloodmeal. All infestations of bibionids have been recorded from affluent neighborhoods where lawns are likely to be heavily fertilized (Ebeling, 1964a). In Florida, sod farm operators report that the larvae of Dilophus orbatus feed on grass roots. Flights of adults are annoying to motorists, but less so than flights of the much larger "lovebug," Plecia nearctica (L. A. Hetrick, correspondence). In England, Dilophus species are believed to be important pollinators of fruit trees (Collyer and Hammond, 1951).

Lovebug, Plecia nearctica Hardy

A native bibionid that has captured public imagination in recent years is the "lovebug," is known in Florida, or,the "honeymoon fly," so named in Louisiana. Other common names are telephonebug, doubleheadedbug, unitedbug. and March fly. These flies range throughout the Gulf states and into Mexico and Central America. They neither bite nor sting, but their mere presence is a nuisance when they occur in large numbers, and they are plagues to motorists and filling-station attendants. The adults in flight splatter on windshields, lights, grills, and radiators of motor vehicles, and their dried remains are hard to remove. They may cause overheating of motors with extensive damage when large numbers are drawn into the cooling systems of liquid-cooled engines. In the northern half of peninsular Florida, there has been a "population explosion" of the lovebug since 1965, but the reason for this is not known. A flight in September, 1969, was estimated to extend over approximately 25% of the land area of Florida, and to reach altitudes of 1,000 to 1,500 ft (300 to 450 m) (Hetrick, 1969, 1970a, b).

Description. The adults are black, with black wings, and with the dorsal portion of the thorax red. The female is 15 mm long and the male is somewhat smaller (figure 322). The larva is slategray, with a darker head capsule. It is 11 to 12 mm long.

Biology. The adults of the first generation fly in May and of the second in September, each for a period of about 4 weeks. The pair mates in flight, and copulation continues until the male dies, flight and crawling being controlled by the larger female. The males live only 2 or 3 days, but the females may live for a week or longer, and may mate with more than 1 male. The mating pairs rest at night, usually on low-growing vegetation. The female lays over 300 eggs in decaying vegetation. The larvae feed on the accumulated decomposed material, often skeletonizing dead leaves. They require adequate moisture and favorable soil temperatures. The pupal stage lasts 7 to 9 days (Hetrick, 1970a).

Control. The flies may be avoided by traveling at night. There is less splattering of them on a vehicle when driving speeds are reduced. Window screen placed between the grill and radiator of an automobile will prevent clogging of cooling fins and overheating of engines. Several minutes of soaking with water will make the fly remains much easier to remove. In May or September, when the adults are in flight, exterior painting of buildings should be avoided.

Scatopsids (Scatopsidae)

These insects were once included in the family Bibionidae. They are small, black or brownish flies, with the appendages and thorax often partly yellowish. The femora of the legs are robust, as with the bibionids, but the legs are somewhat shorter. The antennae have 7 to 12 segments, and are usually slightly longer than the head. There are 3 ocelli (simple eyes), and the proboscis is short and stout (Curran, 1965). The scatopsids were recognized as a separate family by Melander (1916), who stated that the family included "minute black flies, at present bearing the stigma of human disapproval owing to their habit of living in houses but breeding in excrement. Several species have been reared from privies and exposed human feces, and the same species frequently swarm in windows."

Scatopes fuscipes Meigen

A species of scatopsid was found in large numbers on a screen door of a house in Los Angeles, and many had gained entry into the building. They were identified as Scatopse fuscipes, probably the most common scatopsid in this country. The larvae live and feed in all kinds of decaying plant materials, such as cannery waste, winery waste, rotting vegetables, and livestock manure. The best control is sanitation, but if an unidentifiable infestation occurs, dichlorvos may be applied as a spray, and will be quite effective as an insecticide (E. F. Cook, correspondence).


This is the invasion of living tissues or cavities of man or animals by fly larvae (maggots). Similar conditions caused by beetle or moth larvae are called canthariasis and scoleciasis, respectively. Insects of other orders could be involved, but fly maggots account for over 90% of invasions of human beings by insects (Scott, 1964b). Myiasis may be termed gastric, intestinal, urogenital, rectal, nasal, auricular, ophthalmic, or dermal (cutaneous), depnding on the body area invaded. Only accidental or facultative myiasis will be discussed here.

Obligate myiasis, in which the larvae of bot flies or warble flies must live parasitically in the body of an animal, is a veterinary problem, and is not treated in the present volume.

Fly larvae are most likely to enter the human intestinal tract by being swallowed as eggs or young maggots on cold foods, such as meat, cheese, and fruit. The eggs or larvae may be destroyed or digested, in which cases no adverse effects are noted, but they may also survive and cause stomach pains, nausea, vomiting, diarrhea with discharge of blood, and such symptoms as aching of joints and severe nervousness. Myiasis is referred to as "furuncular" if boil-like lesions develop, and "traumatic" if maggots get started in wounds and work their way into healthy tissue. Among cases coming to the attention of the Public Health Service over an 11-year period, 35% were furuncular. Second in number of case was enteric myiasis, with 30%.

James (1947) tabulated 112 species of myiasis producing Diptera in 20 families. The families Calliphoridae and Sarcophagidae contained 34 and 26 species, respectively, or 53.5% of the total. They were particularly important in traumatic myiasis. [James (1947) reported a case of traumatic myiasis involving the sarcophagid Lucilia caesar so serious that it resulted in the amputation of a hand. Merritt (1969) described and illustrated an incredibly horrible infestation by larvae of the calliphorid Phaenicia sericata in large, atrophic ulcers in the legs of an elderly woman who had developed stasis of the lower extremities. It was necessary to amputate both legs. Such a severe infestation could take place only under extremely unusual circumstances, but it indicates that traumatic myiasis remains a potential threat to man.] The third in number of species were the Muscidae, with 15, including the house fly, Musca domestica. The muscids were particularly involved in enteric myiasis.

follicle mite, Demodex folliculorum (Simon) (Demodicidae)

Demodicids are mites that live in the sebaceous pores and hair follicles, usually on the nose, forehead, cheek, and chin. However, they may inhabit follicles, with or without hair, anywhere on the body. When "blackheads" are squeezed out of the skin and examined under the microscope, demodicids are sometimes found, but there is apparently no evidence that the mites cause the blackheads. Demodicids have a curious body form the long, striate abdomen giving them a somewhat wormlike appearance (figure 323). Their legs are mere stumps. They have been found on as many as 97% and 100% of adults examined in different surveys. Children and adolescents are seldom infested. Among adults, those with oily skin or who use cosmetics such as lubricating creams extravagantly and fail to cleanse the skin properly are the ones particularly subject to infestation (Ayres and Anderson, 1932; Ayres, 1963; Ayres and Mihan, 1967; Morgan and Coston, 1964; Coston, 1967). Demodex folliculorum infests hair follicles and D. brevis Akbulatova infests sebaceous glands (Desch and Nutting, 1972). Both may be present on the same individual, but D. folliculorum is the species that has received the most attention.

Description and Habits. The mite is less than 0.4 mm long, and usually escapes notice. Its developmental period is about 14.5 days (Coston, 1967). Inflammation and secondary infection often result when a large number of mites congregate in a single follicle. A Demodex type of acne rosacea or "rosacea-like demodicidosis" affecting the medial portion of the face is believed to result from excessive numbers of follicle mites; it disappears rapidly following the topical application of a suitable antiparasitic medication (Ayres, 1963; Ayres and Mihan, 1967; Morgan and Coston, 1964).

Bacteria have been located on the bodies of D. folliculorum, suggesting the potential of this mite as a mechanical transmitter of disease germs (English et al., 1970).

The follicle mite can cause an inflammatory condition of the eyelids called demodex blepharitis. Many mites can be found clinging to or migrating about on extracted eyelashes. As many as 25 mites have been seen clinging near the root end of a single eyelash, "packed together like sardines" (Coston, 1967). The infested eyelashes may be soggy or waterlogged, and sometimes can be pulled out with virtually no resistance (English,1971).

On Domestic Animals. Demodicid mites infest the sebaceous glands and hair follicles of most mammals, e.g., Demodex canis Leydig (dog), D. cati Mégnin (cat), D. phylloides (Sokor) (pig), D. bovis Stiles (cattle), D. equi Railliet (horse), and D. caprae Railliet (goat) (Coston, 1967). With a "maceration flotation technique," the paired eyelids from a total of 269 cattle, horses, sheep, goats, and deer were examined in the southwestern United States. The mites were found in 11.4% of the cattle, 59.7% of the horses, 11.1% of the goats, but none in either sheep or deer (Baker and Fisher, 1969).

Nearly all dogs are infested (Greve and Gaafar, 1964). In the "red mange" or "demodectic mange" of dogs, Staphylococcus bacteria are generally associated with the mites and their presence complicates the disease.

The disease is most common among shorthaired dogs, and symptoms are first noticed among those that are below the age of 1 year. If lesions are formed, they are usually confined to the head, particularly around the eyes, in the temporal regions, and at the sides of the muzzle, with loss of hair in the affected parts. If the disease is neglected, it may spread from these areas and from other foci that may develop later, and eventually involve most of the body surface (Unsworth, 1946).

Treatment. Most infested persons are women. The greater use of soap and water on the face by men, particularly by those who shave with a razor, results in the face not usually being involved, even when the forehead, and scalp show evidence of infestation. After thoroughly washing the face with soap and water, a prescribed ointment or cream can be rubbed in daily. Danish ointment, a compound polysulfide preparation, has given satisfactory results, and seldom causes irritation when kept away from the eyelids and neck. If Danish ointment cannot be tolerated, a 0.5% selenium sulfide cream can be applied sparingly at night and washed off in the morning (Frazier, 1969). An ointment of 10% sulfur and 5% balsam of Peru is said to be an effective remedy (Busvine, 1966). The improvement can be maintained by washing daily with soap and water.

Demodex blepharitis should be treated early, so that the itching and scratching will not result in abscesses of the eyelids. The services of a physican should be obtaned. Anything that cleanses the mouth of the follicle reduces the number of mites. Vigorously rubbing with a cotton applicator moistened with warm water over the bases of emerging cilia, so as to break apart the collar of insulating debris over the follicle mouth, will reduce the number of mites. The fastest and most direct method of treatment is for an ophthalmologist to apply ether to the lid margins, then after 5 or 10 minutes to apply ether or alcohol again, destroying the emerging mites. This treatment is repeated weekly for 3 weeks, along with a twice-aday cleaning with cotton applicators, followed by appropriate ointments massaged into the lash margin (Coston, 1967).


The enormous numbers of insects and the wide distribution of insects and insect parts in the atmosphere give them, in common with pollens, great potential as excitants of allergic symptoms, particularly those of inhalant or respiratory allergy, that is, asthmalike reactions. The role of insects and insect parts in causing allergies in humans appears to be generally no more than a chance relationship, although some insect parts, such as the urticating (stinging) hairs of certain caterpillars, are apparently specific adaptations for envenomation. Except for the early recognition of such obvious allergenic specializations, scientists have generally been late in recognizing the importance of the arthropods discussed in the present section as sources of allergens. Good examples of this delayed recognition are the house dust mites, the practically universal distribution and importance of which had not become apparent until quite recently. The mites, however, are conspicuous exceptions to the general rule that usually only true insects cause inhalant allergy.

The dispersion of insects by air currents is usually involuntary, particularly for small and feeble-flying species. Insect parts, such as shed skins, scales, and wing particles, may also contaminate the air. Insect fragments, secretions, and excretions, rather than complete and flying insects, are the principal sources of inhalant allergies. More than 1 species is often involved in allergic reactions. Only the more commonly implicated species that are responsible for allergies because of their parts or emanations rather than their bites or stings are discussed here. However, apparently no arthropod species can be definitely stated to be nonallergenic. For example, the house fly was long considered to be incapable of causing allergy, but upon the insistence of an allergy patient, the wing of a house fly was rubbed into a scratch on her skin. Within 15 minutes there was a marked reaction, and several hours later her arm was greatly swollen. An allergic reaction was also obtained by injecting 0.1 ml of fly-wing extract in buffered saline solution into the patient (Jamieson, 1938). The first cases of asthma attacks caused by gnats (Simulium jenningsi) and boxelder bugs (Leptocoris trivittatus) have been reported (Taub, 1970). Cockroach allergy has been studied extensively for years (see near the beginning of chapter 6). However, house flies, moth flies, Simulium gnats, boxelder bugs, cockroaches, dermestid beetles, and many other allergenic insects are discussed in other parts of this volume in connection with pest problems with which they are more commonly associated. Further information on allergic reactions to such insects may be found in those chapters or sections.


Mayflies (order Ephemerids) breed in streams, ponds, and lakes. The young forms (naiads) (figure 324) have 7 pairs of tracheal gills, usually located on the first 7 abdominal segments, by means of which they obtain oxygen from the air dissolved in the water. There is usually 1 generation per year. The adults (figure 324) are attracted to lights, and may enter homes and settle in large numbers on walls or other interior surfaces. This in itself causes mayflies to be pests in communities close to lakes and rivers. In addition, they are among the principal arthropod sources of allergenic emanations and inhalant allergies.

One of the earliest published reports on inhaled insect allergens concerned mayfly swarms (Wilson, 1913). By placing a drop of a mixture of mayfly parts in 2 ml of sterile saline solution to 1 eye of a susceptible person, a marked conjunctival redness resembling that seen in allergy patients was produced, whereas the other eye remained normal. Mayflies are still regarded as important sources of inhalant allergy. These insects do not have allergenic emanations, such as hairs or scales on their wings, as do caddisflies, moths, and butterflies. However, as discussed in the synopsis of orders at the end of chapter 4, the insect molts once more after acquiring wings. After flying a short distance, it alights and sheds its skin, known as a pellicle. This is easily fragmented by a breeze, and its particles may be carried long distances and are often inhaled. Figley (1940) proved repeatedly by conjunctival and inhalation tests that epithelial particles from the pellicles were allergenic. He pointed out that mayflies lived only 36 to 72 hours, dried up very rapidly, and that their dried, fragmented bodies added to the total amount of epithelial scales in the air.


In common with the mayflies, the caddisflies (order Trichoptera) breed in streams, ponds, and lakes, and the adults frequently occur in large numbers in such areas (see the synopsis in chapter 4). The adults (figure 325) are small, dull-colored, mothlike insects, having their wings usually clothed with silky hair; they may be nearly naked in some species, or are rarely clothed with scales. The wings are held rooflike when at rest. Caddisflies have captured the popular imagination because of their aquatic larvae, which build protective cases out of small bits of sticks, leaves, and pebbles which they drag along as they crawl under water with only the head, thorax, and legs protruding (figure 325, D). Some species are herbivorous, feeding upon diatoms, algae, and other forms of aquatic plant life. Others are carnivorous, feeding on midge larvae and other small aquatic animals. Some are both herbivorous and carnivorous. The larvae are important sources of food for freshwater fish, and are also used by anglers as bait.

A book has been published that deals with the biology, ecology, and systematics of caddisflies, with special reference to the larvae, by N. E. Hickin (1967).

The adults are strongly attracted to light, and enormous. numbers collect about street lights, homes, and hotel or theatre marquees. In discussing the situation in a community along the St. Lawrence River, Peterson (1952) stated that the annoyances caused by caddisflies, mainly Hydropsyche bifida Banks, included "complete restriction of all exterior decorating during the summer months; the filth and stench of the masses of dead insects; the necessity, when one drives through the community during the evening flight, of observing the caution normally reserved for dense fog; and the allergic reaction suffered by hypersensitive individuals, locally termed 'sand fever'."

A resident of a river community in Ontario, Canada, suffered asthmatic attacks during the period of caddisfly flights from about the end of June to the middle of September. The patient did not suffer the attacks after she left the infested area. A buffered saline extract of the insects produced positive skin and eye tests. The asthmatic attacks were believed to be caused by hairs and "scaly epithelium" from the wings of the caddisflies. The allergic reaction of the patient ceased about 3 weeks after a series of gradually increasing hypodermic injections of the extract were administered at intervals of 3 to 5 days for a period of nearly 3.5 months. A state of hyposensitiveness was shown by diminished skin and eye reaction, even when the patient was exposed to swarms of the insects (Parlato, 1929). The foregoing test was made in 1929. By 1957, treatment with hyposensitizing injections of caddisfly extract was common in areas infested with these insects. Osgood (1957) reported that of 623 patients suffering from sympoms of respiratory allergy in areas near the Niagara River in New York, 34.5% reacted positively to caddisfly extract, but in the immediate area of heaviest infestation, an even greater percentage (60%) reacted positively.

Moths and Butterflies

Moths and butterflies (order Lepidoptera) are densely covered with scales and hairs, and would be expected to be capable of producing allergenic emanations while in flight or when body or wing fragments are carried about in air currents. Parlato (1932a) exposed glass slides in many locations in Buffalo, New York, and surrounding areas over a 3-year period. He found that on some days the amount of hair and scales was similar to the amount of pollen, and that these emanations were found at various places where people usually assembled. He made tests on 6 patients known to be allergic to caddisfly emanations. Four gave positive skin and eye reactions to the extracts of moths and butterflies, and the other 2 had only a moderate skin reaction. A little "dust" was placed on the conjunctiva of 1 eye of each of the 4 most positive reactors, and these conjunctivae also showed immediate and distinctly positive reactions. On the other hand, among the controls, 10 patients known to be sensitive to the pollens of grains and ragweeds (Ambrosia spp.), and 15 sensitive to other airborne allergens, such as cat hair, feathers, etc., plus 5 individuals with no history of allergy, all reacted negatively to the moth and butterfly extract. However, an office employee with no history of allergy reacted positively. Passive transfer tests made with her blood serum were also positive, producing wheals on a sensitized site of a normal person and on a hypersensitive individual.

In a later investigation, Parlato (1932b) determined that atopic reagins' of the serum of persons who were hypersensitive to the emanations of moths and butterflies were readily transferable to the skin of a nonallergic patient. [Atopic reagins are dermatitis-producing reagins. A reagin is an antibody in the blood of an individual with atopic allergy that is able to sensitize the skin of a normal individual.] He found that the atopic reagin of a butterfly was identical to that of a moth and similar to that of a caddisfly, and that immunologically the 2 orders (Lepidoptera and Trichoptera) could be handled as 1 group.


In 2 studies made in England of insect populations in the air at various elevations, up to 2,000 ft (600 m) in one study and 300 ft (90 m) in the other, aphids (suborder Homoptera) constituted the dominant family of insects at all elevations (Freeman, 1938). In the United States, the astronomical numbers that could be found in the air were noted by Gaillard (1950). He also pointed out that an enormous number of minute particles of aphid exuviae were airborne over wide areas and reached many allergic people. He found that 75 out of 121 allergy patients, whose symptoms were unexplained by tests for known seasonal inhalant allergens, gave positive reactions to aphid extract. Gaillard showed that skin-sensitizing antibodies were present in the blood of skin-sensitive persons, and that the antibody was not antigenically related to ragweed. He believed that the aphid was an important insect inhalant that had theretofore been unnoticed.

Caterpillars with Urticating Hairs

The larvae of Lepidoptera are often called caterpillars, a word derived from the Latin catta pilosa or "hairy cat," and many species are indeed hairy, but many others are hairless. Thus the term "caterpillar" is etymologically quite appropriate for the species to be discussed under this heading. Localized epidemics of envenomation resulting from the urticating hairs of certain caterpillars have occasionally occurred, particularly in the eastern United States. The hairs, which may be hollow, contain a poison that is injected into the skin when their sharp points penetrate. People are affected by pain and rashes when the caterpillars or their shed skins fall on them or when the insects are handled. Kemper (1958) classified the urticating hairs of various genera as to physical types and effects on human volunteers. The hairs can produce a reaction long after the death of the caterpillar, and in fact the dry hairs may then be better able to penetrate the skin. There are many families of Lepidoptera that contain species with nettling (urticating) hairs.

There are several species described or noted here that appear to be the most important ones.

puss moth, Megalopyge opercularis (J. E. Smith) (Megalopygidae)

This moth is widely distributed in the southeastern and south central states, feeding on the foliage of deciduous trees and shrubs, and has caused some of the most serious epidemics of caterpillar dermatitis (Scott, 1964c). No one appears to know why the insects can periodically increase in such large numbers, since it is known that they can be heavily parasitized. More stings were reported in South Carolina in 1960 than during the preceding 25 years combined (Anonymous, 1961 b).

There have occurred a number of epidemics of dermatitis in San Antonio, Texas, so widespread that the public schools were closed until surrounding trees could be sprayed (Foot, 1922).

The mature caterpillar (figures 326, E, and 327) is about 25 mm long, and tapers posteriorly from its widest point in the thoracic region. It may be pale yellow, gray, reddish brown, or a mixture of colors. It is densely covered with hair that lies rather flat and extends downward to the surface upon which the insect rests. Among these hairs are smooth yellowish spines with black tips. The spines are hollow, and a venom passes through them and into the skin of a person contacted (Anonymous, 1961b). Almost immediately after the caterpillar contacts skin, an intense burning is felt. It becomes worse, and is soon accompanied by itching. Small, white papules form, and soon turn red. The inflamed area spreads, and a general swelling of the portion of the body that contacted the hairs may occur; for example, stings on the wrist may cause the entire arm to swell to almost double its normal size and to become numb. The stings are especially severe in young children, who may develop considerable fever and nervous symptoms. The pain is similar to a severe nettle sting. The itching may persist for 1 to 12 hours or even more, and local lesions often remain for several days (Bishopp, 1923). Another stinging caterpillar in the same family of moths is that of the flannel moth, Norape ovina Sepp. The larva (figure 326, C) feeds chiefly on redbud (Cercis sp.; Leguminosae).

saddleback caterpillar, Sibine stimulea (Clemens) (Limacodidae)

The larvae of this family of moths are called "slug caterpillars" because they are short, fleshy, and sluglike. The saddleback caterpillar is green, with a brown, saddlelike mark on its back (figure 326, B). Its hairs can cause severe irritation to the skin. Parasa chloris (Herrich-Schaeffer) (figure 326, A) is another urticating slug caterpillar.

Io moth, Automeris io (F.) (Saturniidae)

The larva of the io moth is a spring-green caterpillar (figure 326, D), having urticating hairs. A narrow, reddish stripe, edged below with white, extends along each side of the body. It feeds on various deciduous trees and on blackberry and currant, and may be found from July to September.

tussock moths (Lymantriidae)

The common name of this family of moths is derived from the long tufts or tussocks of hairs on the caterpillars' bodies. The caterpillars are also conspicuous for their bright, variegated colors. The best known of the lymantriids are the gypsy moth, Porthetria dispar (L.), and the browntail moth, Nygmia phaeorrhoea (Donovan), both Old World species that are now serious pests of forest and shade trees in the eastern United States. The browntail moth is well known for its urticating hairs. The adult moth has a white thorax, white wings, and a wingspread of 25 to 40 mm. The abdomen is mostly brown, and the common name is derived from the conspicuous tuft of chestnut-brown hairs at its tip. The full-grown caterpillar is about 40 mm long, dark brown, with a row of white tufts on each side of the body. There is a bright-red tubercle on the back of the eleventh and of the twelfth body segment. The nettling hairs of the caterpillar are responsible for the "caterpillar dermatitis" or "browntail rash" that is common in infested areas. Pruritus occurs 20 to 30 minutes after contact, followed by inflammation and wheals. The eruption can be generalized if the larval hairs become lodged in clothing, and the patient will be exposed to an attack every time the clothing is worn. Attacks from this species usually occur in May and June, the months of larval development (Sutton and Sutton, 1939).

The term "tussock moth" also commonly refers to the species of Hemerocampa. The species usually implicated in irritating skin rashes are the whitemarked tussock moth, H. leucostigma (J. E. Smith), in the eastern states, and the Douglas fir tussock moth, H. pseudotsugata McDunnough, in the western states. The females of these moths are wingless. They lay their eggs on or near the cocoons from which they emerge, and cover them with froth and the hairs from a tuft at the tip of the abdomen. Hibernation is in the egg stage. The caterpillars are serious defoliators, attacking mainly forest and shade trees. They move to lower levels by means of silken threads in search of food, and may often be seen hanging on them. Their long hair and light weight allow them to be carried long distances by the wind, particularly in their early instars, thereby spreading the infestation.

The male of H. leucostigma has a wingspread of about 30 mm, and its forewings are gray, with darker wavy crossbands. The full-grown caterpillar is 30 to 35 mm long, and is light brown with yellow and black stripes. It has a bright-red head and a bright-red spot on the sixth and seventh segments of the abdomen. There are 4 short, white, dorsal tufts of hairs on the first 4 abdominal segments, a long pencil-like tuft of black hairs on each side of the head, and another near the posterior end. The caterpillars skeletonize the leaves of deciduous forest, shade, and sometimes fruit trees.

The male of H. pseudotsugata has a wingspread of about 25 mm, and is dull brownish gray. The full-grown caterpillar is 20 to 25 mm long, and is gray to light brown. It has a shiny black head, many red spots, and broken, narrow, orange stripes along the sides. There are short, brushlike tufts of light-brown or cream-colored hairs on the first 4 and the last abdominal segments, and 2 anterior, black, pencil-like tufts of black hairs and a longer posterior one. There is 1 generation per year.

Hemerocampa pseudotsugata is principally a pest in the Pacific Northwest, defoliating Douglas firs and true firs. In August, 1973, there was a severe infestation of the pest in about 800,000 acres (324,000 ha) of forest in Oregon and portions of Washington and Idaho, and the infestation has been spreading. The federal ban on DDT leaves authorities with no effective control measure. An infestation is usually controlled by a virus within a 3-year period, but this has not yet happened in the present case. There have been numerous instances of skin rash, particularly among loggers (Hager, 1973).

Blister Beetles (Meloidae)

Blister beetles are narrow, elongate insects, with soft and flexible elytra and with the pronotum narrower than either the head or the elytra. Their bodies contain a crystalline anhydride of cantharidic acid called cantharidin. The beetles exude the vesicating venom when disturbed. They fill their tracheae with air, close their spiracles, and build up body-fluid pressure until breaks occur in the exoskeleton, usually at joints. Body fluids containing cantharidin then spill through the breaks (figure 328). The beetles proceed to relieve the pressure, and the wounds heal. If they are handled during or immediately after this process, the cantharidin contacts the skin and produces fluid-filled blisters that may eventually burst. The released fluid often produces secondary blisters, and sometimes secondary infection, especially impetigo. Persons with such blisters are advised to consult a physician. If the blisters do not break, the fluid is slowly resorbed in 3 or 4 days (Swarts and Wanamaker, 1946; Lehmann et al., 1955. Scott, 1962, 1966b).

Some Common Blister Beetles

Epicauta cinerea (Förster), the clematis blister beetle, is the species most commonly seen in the southwestern United States. In common with other species of the genus, it is known to produce symptoms of dermatosis. It is 10 to 17 mm long, black, and uniformly clothed with gray pubescence.

Scott (1962) recorded the case of a woman in Georgia who brushed an Epicauta off her neck, then crushed it, picked it up in a piece of paper, and brought it to his laboratory for identification. Within 12 hours, 3 large blisters had developed on her neck, and the affected area was still painful after 48 hours. An entomologist who handled the paper in which the beetle had been wrapped developed a blister on one finger.

Epicauta maculata (Say), the spotted blister beetle, is light brown over-all, including the legs, and is dotted with round, black spots (figure 328). It is medium-sized, varying from 9.5 to 16 mm in length (Gilbertson and Horsfall, 1940).

Epicauta vittata (F.), the striped blister beetle, is said to be the most common species in the eastern United States, and extends westward as far as Montana. It is 12 to 14 mm long, blackish, with each elytron bordered yellow, and has a median yellow stripe.

Epicauta pennsylvanica (De Geer), the black blister beetle, is common not only in the eastern states, but ranges from Mexico through much of the country. It is 7 to 13 mm long, and uniformly black (Essig, 1926; Lehmann et al., 1955).

Biology and Habits. Blister beetles have a comparatively complex life history. They undergo a hypermetamorphosis, with a variety of larval forms (figure 329). The eggs, laid in cavities prepared in the ground, hatch into long-legged forms called triungulins. The triungulins of most species search for pods of grasshopper eggs, but others climb upon flowers and attach themselves to solitary bees, which then carry these very active and agile larvae to their nests, where the triungulins feed on the bees' eggs. The next larval instar is similar to the triungulin, but has shorter legs. The third, fourth, and fifth instars become increasingly scarabaeiform (grublike). The sixth instar, called the coarctate larva or pseudopupa, is the hibernating instar. It has a darker and thicker exoskeleton and lacks functional appendages. In the spring, it molts and becomes the seventh instar, which is small, white, and legless, but active. This instar transforms into the true pupa. The adult emerges in about 2 weeks, and normally there is 1 generation per year (Gilbertson and Horsfall, 1940; Horsfall, 1943).

Some blister beetles are important pests, feeding on potatoes, tomatoes, and other crops. Outbreaks of the beetles tend to occur in years of severe grasshopper infestations (Gilbertson and Horsfall, 1940). Epicauta cinerea often occurs on Cineraria, and E. pennsylvanica usually prefers goldenrod (Solidago spp.), although it is found on other plants, and is sometimes injurious to various truck crops. Workers in potato fields where large numbers of blister beetles are feeding may get blisters on exposed surfaces of their bodies. Barefooted children sometimes crush the beetles and get a large amount of cantharidin on their feet. They should be advised to avoid walking, and to apply wet dressings to their feet for 24 to 48 hours, followed by one of the antibiotic dressings (Lehmann et al., 1955).


Millipedes (class Diplopods) live in dark, moist places, and feed principally on decaying vegetable matter (see chapter 10). They may climb the sides of houses in large numbers after nightfall, and many may find their way into a home. The species of some genera exude a vesicating venom that causes blisters on persons handling them. However, they are mostly nuisances (Scott, 1966b).

house dust mites, Dermatophagoides pteronyssinus (Trouessart) and D. farinae Hughes (Pyroglyphidae)

Among the many constituents of house dust that cause allergic reactions of the respiratory tract (rhinitis and asthma), the most potent allergens were found by European investigators to be contained in, certain pyroglyphid mites, principally Dermatophagoides pteranyssinus (Voorhorst et al., 1964). On the other hand, all mites found in dust samples in Ohio were classified by D. G. Larson as the closely related species D. farinae, although F. T. M. Spieksma, of Leiden, the Netherlands, identified D. pteronyssinus in some of the Ohio samples (Mitchell et al., 1969). Samgihak et al. (1972) found D. farinae to be the dominant species in Czechoslovakia. They believed that D. pteronyssinus favored the coastal climate, whereas D. farinae favored the drier central European climate. The taxonomic positions of the species of Dermatophagoides were clarified by Fain (1967). Although Dermatophagoides was not experimentally demonstrated to be a cause of common house dust allergen until 1964 (Voorhorst et al., 1964), a review of the world literature in 1971 already disclosed 103 references (van Bronswijk and Sinha, 1971).

Dermatophagoides pteronyssinus and D. farinae are cosmopolitan, and are sometimes found in enormous numbers (Voorhorst et al, 1964; Miyamoto et al., 1969b). The fecal pellets of either species are comparable to the mites, or extracts from them, as sources of allergen. Fortunately, most people are not sensitive to these mites fewer than 5% of children under 17 years old and even fewer adults (Spieksma, 1967; Larson et al., 1969; Mitchell et al., 1969; Miyamoto et al., 1969b; Halmai and Alexander, 1971).

In one survey of 64 samples of house dust obtained from Connecticut, New York, New Jersey, Georgia, Washington, California, Nebraska, Wisconsin, and Illinois, 39 contained house dust mites. Twenty-one had D. farinae only, 5 had D. pteronyssinus only, and 11 had D. farinae and D. Pteronyssinus. Dermatophagoides farinae was not only found in more samples, but also in greater numbers: up to 69 per gram compared with 9 per gram for D. pteronyssinus. Besides being found in house dust, Dermatophagoides species are also found on birds, in bird nests, on various animals, and humans, as well as in stored food products. Dermatophagoides evansi Fain and D. chelidonis (Hull) were found most commonly in bird nests (Wharton, 1970). Mites were found in 10 out of 26 house dust samples randomly collected from floors and mattresses with vacuum cleaners in Canadian homes of persons with or without allergies. Four of the 10 samples had D. farinae, 3 had D. pteronyssinus, and 1 had both species. Of the 57 mites collected, 48% were D. farinae, 17% were D. Pteronyssinus, and most of the others were stored-product species (Sinha et al., 1970). Based on published and unpublished reports of house dust mites in the United States, Dermatophagoides species, principally farinae and pteronyssinus, had been isolated from house dust samples in 22 states by 1971. Dermatophagoides evansi, D. chelidonis, D. bakeri Fain, and D. scheremetewskyi Bogdanov were found in very small numbers. House dust samples ranged from 32 to 100% positive for species of the genus, and they constituted from 43 to 100% of the mite fauna. In California, these mites were found in house dust samples from 24 widely scattered areas (Furumizo and Mulla, 1971).

In Hawaii, house dust was collected with vacuum cleaners over an 8-month period in 40 houses. Dermatophagoides was found in all the samples obtained, D. pteronyssinus being much more abundant than D. farinae. The maximum number of Dermatophagoides in a 5-gram dust sample was 4,390, a much higher density than any reported from house dust in other parts of the world. Dust from carpets (wool, cotton, or svnthetic fibers) always had more mites than dust from floors without carpeting or with other types of coverings. Old carpets not cared for had more mites than newer ones or those often cleaned and washed (Sharp and Haramoto, 1970).

Dermatophagoides pteronyssinus was found in all of 250 homes visited throughout New Zealand, except for one in which the occupant had been treating the mattress at frequent intervals with sulfur dust. Except for this one house, the number of mites varied from 2 to 480 per 0.1 gram of dust in the 300 dust samples (Corners, 1972).

Description. The mites are extremely small. The adult female mites of D. farinae (figure 330) are about 0.5 mm long; tritonymphs and males, about 0.4; protonymphs (figure 331), 0.3; larvae, about 0.2; and eggs, close to 0.3 mm long. The adult mites are light cream-colored, except for a few areas of sclerotized integument (propodosomal dorsal plate and parts of the appendages), which are light beige (G. W. Wharton, correspondence).

Life Cycle. Pyroglyphids have 5 distinct life stages: egg, larva, protonymph, tritonymph, and adult. For D. farinae and D. pteronyssinus, the developmental period from egg to adult ranges from 23 to 30 days. Males and females of both species have a premating period of 1 to 3 days. The male remains fertile for life, but mating results in egg-laying only during the first half of the adult life of the female.

At a temperature of 25 °C, the first oviposition period for D. farinae lasts about 30 days, with 0.8 to 1.4 eggs laid per day. The first oviposition period for D. pteronyssinus is 20 days, with 1.2 to 2.5 eggs laid per day. Both species have a second and even a third oviposition period, but fewer eggs are laid (van Bronswijk and Sinha, 1971).

The life cycle of D. farinae is very similar to that of D. pteronyssinus, but the period from egg to adult averages 4 days longer. In both species, no eggs are laid unless copulation has occurred (Larson et al., 1969).

Habitat. Both the mite species are found principally in cotton-stuffed mattresses and furniture (Cunnington and Gregory, 1968; Mitchell et al., 1969).

In a hospital in England, it was shown by means of a cyclone dust extractor that the mites could become airborne during bedmaking, including turning the mattress (Cunnington and Gregory, 1968). In other investigations, it was shown that mites could be inhaled (Carter et al., 1944; Taboada, 1954; Spieksma, 1967).

In central Ohio, Mitchell et al. (1969) made a survey of dust samples and, using a dissecting microscope, they removed all mites and all recognizable cuticles or exoskeletons of mites from 0.1 g samples of fine dust. They never found living mites in dry dust. Mite cuticles or dead mites were found in 21 out of 30 samples of dust from mattresses and padded furniture, and 17 samples had more than 15 mites per 0.1 g. Floor sweepings and dust from commercial buildings contained either no mites or negligible numbers. Articles which were used by humans both day and night, such as day beds, contained the most mites. Mites were rare or absent in articles of furniture that had not been used by humans or were not stuffed with vegetable fibers.

Mitchell et al. (1969) believed that the mites probably fed primarily on dander (skin scales) from humans and pets. However, they have also been reared on human whiskers in a special microchamber (Shamiyeh et al., 1971). Additional information on possible food sources was provided by van Bronswijk (1973a) in an investigation of 470 Dermatophagoides pteronyssinus from mattresses and 147 from bedroom floors. Their alimentary canals contained pollen, spores of microorganisms, fungal mycelia, bacteria, and fibers of plant origin, probably from cotton bedsheets. This indicated that the mites were not so strictly monophagous on human skin scales as was sugested by Spieksma (1967).

Laboratory tests revealed that optimal development of D. pteronyssinus took place at 25 °C (77 °F). After 8 weeks at 30 °C (86 °F), the number of mites was 40%, and at 20 °C (68 °F), it was only 15% of the number at 25 °C. The mites can develop within a range of 50 to 90% relative humidity, the optimum being 70 to 80%. In the Netherlands, only in summer is relative humidity in houses high enough to allow rapid increase in the mite population. Although the average temperature on floors in summer is usually below 20 °C (68 °F), in occupied beds and upholstered chairs optimal temperatures are soon reached, and relative humidity is increased by 5 to 8% (Koekkoek and van Bronswijk, 1972).

In the Netherlands, D. pteronyssinus is present in greatest numbers in old houses, and that is where most of the people live who are hypersensitive to house dust allergen (Voorhorst, 1969). In Europe, "house dust atopic asthma" patients find relief in the dry conditions at altitudes of about 1,000 m (3,300 ft) or higher. The cold air, soil conditions, and a type of construction providing good protection against the penetration of water result in dry conditions in houses. The dryness prevents the development of large numbers of allergen-producing D. pteronyssinus (Voorhorst, 1970; Spieksma et al., 1971).

Dust Mites and Inhalant Allergy

Although the allergen is formed by living mites, dead mites or their fragments or feces are allergenic as well as live ones. Maunsell et al. (1968) observed that asthmatic patients who reacted negatively to house dust were negative to the mites. Mitchell et al. (1969) found that 93% of the patients who showed positive skin reactions to house dust extract also showed positive reactions to the extract of mites, and vice versa. Out of 100 patients who showed reactions to dust mites, 61 reacted positively to 1 or more insects and/or spiders. Bernecker (1970) observed that a certain cross-antigenicity existed, not only between mites occurring in house dust, but also among mites in general, including species such as Tetranychus urticae, Panonychus ulmi, and Dermanyssus gallinae, which are not ordinarily found in house dust.

Mites constitute the major antigenic substance in house dust in Japan. More than 35 species of mites were found in house dusts collected from 9 different parts of Japan, and 1 g of dust contained from several hundred to over 2,000 mites. The major allergen was possessed by D. pteronyssinus (27.2% of the total number of mites) and D. farinae (4% of the total), the 2 species having a close antigenic relationship. Cross-antigenicity was found from skin testing, and in vitro neutralization of skin-sensitizing antibody, among the 6 species of mites investigated. Molds were found to be of little importance as allergens (Miyamoto et al., 1969b). The molecular weight of the allergen produced by Dermatophagoides farinae is greater than 10,000 but less than 69,000 (most likely around 40,000 to 50,000), and it is probably a protein and polysaccharide conjugate. Work on the chemistry of the allergen is continuing. Dermatophagoides farinae develops readily on dog meal, and is available in larger quantities for scientific investigations than is D. pteronyssinus, which must be reared more slowly on human dandruff (Miyamoto et al., 1969a).

Reactions to Various Tests. In England, tests with extracts of D. pteronyssinus were made on skin, bronchi, nasal mucosa, leucocytes, and on normal human tissue passively sensitized by the patient's serum, on 21 patients with asthma and house dust allergy. Fourteen patients gave positive reactions to every test. In 18 patients, attacks were readily induced by inhalation of the mite extract. In 18, nasal reactions were provoked, and were not followed by asthmatic symptoms. A serum test was positive in all patients, and a leucocyte test was positive in 19. In 6 patients, delayed asthmatic responses to bronchial tests were observed. An extremely small amount of allergen was capable of causing a reaction. In view of the wide distribution of D. pteronyssinus, it was concluded that it was an important factor in allergic asthma (McAllen et al., 1970).

Desensitization tests were made with 34 persons suffering from bronchial asthma and showing positive skin reactions to house dust and D. farinae. Eighteen patients were given mite extracts and 16 were given house dust vaccine in weekly subdermal injections of 0.1 to 1.0 ml, followed by semimonthly maintenance doses for 6 to 9 months. Hyposensitization with D. farinae extracts was found to be safe and effective, but patients did not benefit from house dust vaccine in the doses administered (Maunsell et al., 1971). The absence of positive results with house dust vaccine was not in accord with the results obtained by another investigator, who desensitized 11 patients with house dust extract and 13 others with Dermatophagoides pteronyssinus extract. Skin reactions to both extracts decreased to about the same extent over the period of 1.5 to 2 years of the tests (Voorhorst, 1970).

In a hospital in England, patients with asthma and rhinitis who were clinically sensitive to house dust mites were treated with a pyridine-extracted, alum-precipitated extract of house dust to which D. farinae had been added before extraction. Among 52 patients, 43 (83%) showed improvement. Symptoms were worse or unchanged in 9 patients (17%) (Munro Ashman et al., 1971). In a "double-blind" controlled trial, 11 asthmatics allergic to house dust who were given an aqueous extract of D. pteronyssinus improved and 5 remained well for a year, whereas 11 control patients, given an extract of human skin scales, showed little change (Smith, 1971).

Other Mites Causing Allergy

The family Acaridae (=Tyroglyphidae) contains species best known as pests of stored food products (see chapter 7, under "Acarid Mites"), but some species also cause dermatitis in people handling infested commodities, as well as causing inhalant allergy or bronchial asthma. Acarus siro L. causes a rash known as "vanillism" in vanillapod handlers. Tyrophagus castellani (Hirst) causes "copra itch" among workers handling copra and a dermatitis in people who handle cheese. In the family Glycyphagidae, Glycyphagus domesticus (De Geer) causes "grocer's itch" in workers handling dried fruits, skins, and other heavily infested products. Allergen from Glycyphagus destructor (Schrank) was found in chaff (Voorhorst, 1970). Allergen obtained from G. destructor differs materially from that of the 2 house dust mites, Dermatophagoides pteronyssinus and D. farinae, whereas the allergens of the latter 2 species are identical (Voorhorst and Spieksma, 1969).

In the family Pyroglyphidae, Dermatophagoides scheremetewskyi attacks bats, rodents, and sparrows in the eastern United States. Several cases of human infestation resulting in severe and persistent dermatitis have been reported (Traver, 1951; Baker et al., 1956). However, species of this genus are best known as the ones causing inhalant allergy.

Control of Mites Causing Inhalant Allergy

The 4 sources of dust mite allergen in houses are floors, mattresses, furniture, and clothes (van Bronswijk and Sinha, 1971). The number of mites on floors can be reduced by keeping the house dry. The optimal relative humidity for pyroglyphid mites is from 75 to 95%. Under conditions suitable for all mite species, Dermatophagoides can survive only in small numbers in cracks and crevices, but at lower humidities not suitable for Acarus and Glycyphagus, Dermatophagoides may greatly increase in numbers. None of these mites can survive under very dry conditions (van Bronswijk et al., 1971). Motile stages of D. farinae and D. microceras were eradicated by 6 hours of exposure to -15 °C (5 °F), whereas D. chelidanis, D. pteronyssinus, and Euroglyphus maynei (Correman) required -28 °C (-18 °F) for the same period of exposure. One-day exposure of mattresses to the outdoor air has been suggested for the control of pyroglyphid mites in areas where sufficiently low temperatures are reached (van Bronswijk and Koekkoek, 1972).

Small cracks and crevices in the floor and under plinths should receive greater attention when vacuum-cleaning. Under conditions obtaining in the Netherlands, it was observed that the habit of Dermatophagoides to hide in cracks and crevices tended to favor these mites, relative to Acarus, Glycyphagus, and Tyrophagus, when a floor was vacuum-cleaned, thus eliminating the latter 3 genera as competitors and also eliminating large numbers of the predatory mite Cheyletus. Thus, it was sometimes possible to find the highest numbers of Dermatophagoides in regularly vacuum cleaned rooms (van Bronswijk et al., 1971).

After mattresses were vacuum-cleaned, there was an 8-fold reduction in the number of mites that became airborne during bedmaking. Dead mites and mite excreta possessed as much allergen as live mites, and vacuum-cleaning was necessary after the mites were killed. Ultraviolet radiation for 2 hours almost completely removed the allergen (van Bronswijk,and Sinha, 1971). Mattresses appear to be the reservoirs from which bedroom floors are reinfested by dust mites for a brief period during the year (van Bronswijk, 1973a). The mites apparently live only in the surface layer of the mattress (Hughes and Maunsell, 1970; van Bronswijk, 1973a). It is reasonable to expect that control of dust mites in bedrooms inhabited by persons who are allergic to dust mites may be accomplished by preventing penetration of moisture and accumulation of food in the upper few centimeters of the mattress, as with the aid of a plastic sheet. Experiments on this approach to dust mite control are in progress (van Bronswijk, 1973a). Also, the application of fungicides to eliminate microorganisms that are essential to the mites appears to be a promising approach (van Bronswijk and Koekkoek, 1971; van Bronswijk, 1973b).

Frankland (1972) recommended that environmental mite control should always be attempted in the home of an allergic person before hyposensitization. Feather and kapok pillows and eiderdowns should be removed. Blankets should be dry-cleaned, and the linen washed whenever possible. At least once a week, the house should be vacuumed and the bedroom more often, paying special attention to cracks and crevices. Helson (1971) suggested ventilation, vacuum-cleaning, dusting of 1% lindane dust into cracks and crevices and, if an acaricide were used, the removal of all dead mites, cast skins, and fecal pellets. On the other hand, van Bronswijk et al. (1971) reported little effect from a 24-hour exposure of Dermatophagoides to residues of 0.1% and 1.0% of lindane and DDT, in acetone, that had been applied to the ceilings of cages containing approximately 20 mites. Other mites (Acarus and Glycyphagus) were very susceptible to the residues.

Figure Legends

Fig. 314. Clear Lake gnat, Chaoborus astictopus. A. male; B, female; C, pupa; D, eggs; E, larva; F, eversible pharyngeal sac extended from the mouth. (From.Herms, 1937.)

Fig. 315. Chironomid midges, Chironomus plumosus, massed against a building. (Courtesy E. C. Bay.)

Fig. 316. Female Chironomus plumosus completing oviposition. (From Bay, 1967.)

Fig. 317. Expanded egg mass of Chironomus plumosus, with unexpanded egg mass below. (Courtesy E. C. Bay.)

Fig. 318. A widely distributed chironomid midge, Chironomus attenuatus (male).

Fig. 319. Chironomus californicus. Left, female; right, male. (From Ebeling, 1964a.)

Fig. 319A. Moth flies (Psychodidae). Top, adult fly and larva; bottom Telmatoscopus albipunctatus. (Top drawing from Scott, 1961c.)

Fig. 320. Eye gnat, Hippelates collusor. Left to right, eggs; larva; pupa; adult. (From Hall, 1932.)

Fig. 321. A March fly, Dilophus orbatus. (From Ebeling, 1964a.)

Fig. 322. Lovebug, Plecia nearctica. Top, male (left) and female; bottom, larva. (From Hetrick, 1970a, b.)

Fig. 323. Follicle mite Demodex folliculorum. Fifteen mature and 4 immature forms, greatly magnified. (From Ayres and Mihan, 1967.)

Fig. 324. A mayfly, Ameletus amador Mayo. Above, adult; below, nymph or naiad. (From Chandler, 1956.)

Fig. 325. Caddisflies. A, Dolophilus shawnee Ross; D, Rhyacophila fenestra Ross; C, larva of Rhyacophila fenestra, D, Ochrotrichia unio (Ross), larva and case. (From Ross, 1944.)

Fig. 326. Some important species of stinging caterpillars in the United States. A, a slug caterpillar, Parasa chloris, B, saddleback caterpillar, Sibine stimulea; C, a flannel moth caterpillar, Norape ovina; D, io moth caterpillar, Automeris io; E, puss caterpillar, Megalopyge opercularis. (Scott, 1966b.)

Fig. 327. Larva of puss moth, Megalopyge opercularis, on an orange leaf. (Courtesy Helen L. Greene.)

Fig. 328. Spotted blister beetle, Epicauta maculata, exuding a drop of vesicating venom from a break in a weak spot of its exoskeleton. (From Scott, 1966b.)

Fig. 329. Larval and pupal stages of the black blister beetle, Epicauta pennsylvanica. A, unfed first instar (x 13); B, fully fed first instar (x 13); C, D, E, second, third, and fourth instars (x 13); F, newly molted fifth instar (x 7); G, gorged fifth instar (x 7); H, sixth instar (x 4); I, seventh instar (x 4); J, pupa (x 4). (From Horsfall, 1943.)

Fig. 330. Ventral view of male (left) and female of the North American house dust mite, Dermatophagoides farinae. (From Fain, 1967.)

Fig. 331. Protonymph of the house dust mite Dermatophagoides farinae. (From Wharton, 1970.)

1996; 2002© Entomology UC Riverside
Last updated on Aug 23, 2002 by leowest@ucrac1.ucr.edu