Pests in Excessively Damp Locations
- Sources of Moisture in Buildings
- Fungus Beetles
- Miscellaneous Mites and Insects
- Sowbugs and Pillbugs
Modern homes in the United States provide particularly favorable refuges for certain pests attracted to excessively damp locations. In some areas, the problem is aggravated to some extent by hollow walls, as in wood-frame and some other types of construction. Wall voids provide seclusion and sometimes considerable moisture for the growth of fungi upon which certain insects can feed. They are accessible to insects via the space around utility pipes and electrical conduits that enter through the framing, and also through imperfections in construction. Similar entry routes also result in accessibility between wall voids and the attic. Insects may enter the attic through screened or louvered vents, under shingles, or through chinks, cracks, and crevices in the roof and eaves. The typical construction also provides for enclosed spaces under cabinets, pantries, closets, bookshelves, and built-in appliances. These favored areas for cryptobiotic insects may be accessible because of imperfections in design and construction or because of faulty construction materials.
Buildings with sliding glass doors, particularly on slab-on-ground foundations, sometimes allow the entry of certain pests from moist, shady, or secluded places, such as sowbugs, pillbugs, springtails, millipedes, centipedes, earwigs, or oriental cockroaches. Enclosed patios, often with considerable decorative vegetation, have resulted in the introduction of plant pests and soil or humus inhabiting pests into the home. The soil adjacent to the foundation is often shaded, damp, and contains abundant humus and fertilizer. Greater emphasis on the beautification of the yard and garden often involves extensive cultivation of trees, shrubs, flowers, and lawns. Wooden and brick planters are becoming increasingly popular. The insect and other fauna associated with such areas may enter the house directly around doors and windows or via subfloor areas which are protected from the sun and are often cool and damp.
Some pests, such as cockroaches and earwigs, that are favored by both moisture and seclusion, and others, such as silverfish, carpet beetles, cluster flies, face flies, and some species of ants, that are favored primarily by seclusion, have been treated in other chapters of this book under what appear to be more appropriate headings. The insects and other arthropods considered in the present chapter are those that are attracted to any damp area, usually feeding on fungi, and are found in such enclosed places as wall voids only when those spaces become excessively damp for long periods. Among them are fungus beetles, fungus gnats, fungus moths, psocids, springtails, and certain mites. These arthropods all have a protective film of lipid covering their entire cuticles and protecting them from a lethal rate of water loss, even in dry environments. With the exception of the springtails, they are not compelled to live in damp areas, but seek them because they find food there, such as leaf mold or fungal mycelia. (See under "Springtails" in this chapter.) There are other arthropods, such as sowbugs, pillbugs, amphipods, millipedes, and centipedes, that must live in damp areas because they lack the protective lipid film possessed by insects and mites. These are not the pests that deliberately infest damp locations in the home, but must live in the even damper conditions found in many areas surrounding or beneath the house, such as under piles of leaves, grass, peat moss, wood chips, in damp leaf mold, or in cracks in damp earth. They enter homes only as accidental intruders, and cannot.survive there.
SOURCES OF MOISTURE IN BUILDINGS
Although leaky roofs, poor flashings, inadequate sidewall construction, and plumbing leaks are common sources of excessive moisture in homes and other buildings, condensation within buildings has become a more important factor in much of the United States. Condensation problems are obviously different in cold and temperate regions from those in warm, humid ones. Cold-weather condensation is most likely to occur in North America north of 370 latitude (excluding the Pacific Coast strip) where the average January temperature is below 35 °F (17 °C). In this region, temperature differential results in vapor pressure inside a house being several times higher than outside, so that moisture tends to move outward through cracks, crevices, and building materials, and is most likely to condense on some cold surface, such as the outside face of sheathing, the back and inside faces of siding, on the undersides of roofs, and on chimmneys. The moisture generally condenses in the form of ice or frost. The frost melts during warm periods, and in the more severe cases, water in the attic may drip to the ceiling below and cause damage to the finish. Cold-weather condensation can be prevented by placing moisture barriers (treated papers, foils, films, or coatings) on the warm side of insulated walls and ceilings (Anderson, 1972).
In warm, humid regions, such as the Gulf Coast of the United States, air-conditioning is the cause of most condensation problems. Although it might appear, that warm-weather condensation should be prevented by placing a moisture barrier on the warm side (outside) of an insulated wall, research has shown that a moisture barrier installed under wooden siding may lead to serious accumulations of moisture within the siding. Progress in the prevention of condensation in insulated walls in warm, humid regions will depend on further research, but it is already evident that such walls will be relatively free of condensation moisture if they are reasonably permeable to water vapor. Serious condensation of moisture can occur in wooden floors in air-conditioned homes in warm, humid areas if inside temperatures are not maintained below 75 °F (24 °C). Such condensation problems can be prevented by decreasing the humidity of crawl spaces through proper ventilation, soil drainage, soil covers, or mechanical dehumidification (Amburgey, 1972).
A major cause of condensation has been the increase in the daily use of water by occupants of buildings. Each day, a typical family of 4 converts about 25 lb (11 kg) or approximately 3 gal (11 L) of water into water vapor in the air of an average house (Anderson, 1972). High water tables, garden irrigation, etc., can introduce as much as 100 lb (45 kg) of water per day per 1,000 sq ft (93 sq m) into building subareas. If this water is not removed by proper ventilation, it is conducive to infestation by insects and other pests as well as infection by decay fungi (NPCA, 1955).
Rooms are smaller and more airtight than they were a few decades ago, resulting in less air to absorb and disperse the moisture released in household operations. Relative humidity is generally higher than it was in houses built many years ago. The latter generally had large rooms with high ceilings, windows that were not weather-stripped, and their construction details allowed greater air loss and air infiltration. Through central heating, all rooms within a house are likely to be warm, resulting in largescale condensation on and in the cold walls. Water condensing on windowpanes runs down into the sash, sills, framing, and often onto the walls. More houses are being built on concrete slabs, for which there is no subfloor ventilation, and even for conventional construction, ventilation is often inadequate in subfloor areas and attics, which also helps to retain the moisture within the house. With joist-type construction, an effort should be made to ensure adequate ventilation of the crawl space, and a vapor barrier over the soil may be desirable. The moisture problem can also be minimized by keeping windows closed during the day, using a dehumidifier, and raising the inside temperature (Anderson, 1972).
Excessive moisture can result from humid weather, leaky roofs, wet basements, manufacturing and processing operations, evaporative air coolers, and inside venting of plumbing or of machines such as automatic clothes driers (they should be vented to the outside). Clothes driers should be particularly emphasized in this connection because the vent of the machine not only blows hot, humid air into the building, but also contributes a large amount of organic lint that coats the walls and furniture, and upon which mildews can flourish. Insects such as fungus beetles, psocids, and springtails can subsist on the mildew spores (Scott, 1966c).
The construction of concrete or masonry floors, walls, and fireplaces requires large volumes of water. In the construction of a small home with a basement, the concrete floor would have more than 2,000 lb (908 kg) of water when it is poured, the concrete basement walls would have over 4,000 lb (1,816 kg) and, if the house is plastered, over 2,500 lb (1,135 kg) of water would be used for that purpose. The rough frame of a house may be damp when constructed, and rain may add more water before the roof and sidewalls are completed. Because of rapid completion of the building, this water may remain in the house or apartment structure for months after occupancy.
Green lumber is occasionally used in construction, and the building is then quickly enclosed, giving the lumber little chance to dry. This results in "sweating" and high humidities in wall voids, favoring the growth of molds upon which insects can feed. Pests such as fungus beetles and psocids are often problems associated with new construction. When the building is occupied, the artificial heating required for human comfort eventually dries out the lumber, and infestation by mold-feeding insects then seldom reoccurs (NPCA, 1955; Anderson, 1972).
(Mostly Lathridiidae and Cryptophagidae)
- Some Common Species
- Fungus Beetles Feeding on Moldy Stored Food Products
- Feeding Habits of Fungus Beetles
- Economic Importance
- Control of Fungus Beetles
Fungus beetles in the above 2 families are feeders on fungi in damp areas within buildings. They are sometimes colloquially called "plaster beetles" by pest control operators. This name was originally suggested by the occurrence of these beetles in the walls and living spaces of new buildings that had been plastered and remained damp longer than usual because of the water released by the plaster or from other sources. Moisture and warmth favor the growth of molds upon which the beetles feed.
Description. Fungus beetles are very small insects, ranging from 1 to 3 mm in length. They are various shades of brown, varying from light yellowish brown to nearly black. Morphological features of the 2 families are illustrated by the lathridiids Cartodere constricta (Gyllenhal) and Aridius nodifer (Westwood), and the cryptophagid Cryptophagus laticollis Lucas (figure 332). Lathridiids usually have rough surfaces, and the elytra are conspicuously marked by rows of pits and are broader than the exposed parts of the thorax and head. The bodies of cryptophagids are always more or less convex, while those of lathridiids may be convex or flattened, depending on the species. Most of them are unable to fly.
The antennae of lathridiids are 8 to 11-segmented, and have 1 to 3-segmented terminal clubs. The antennae of cryptophagids are always 11-segmented, and usually have loose, 3-segmented clubs, but in a few species these clubs are 2 or 4-segmented. The tarsi of lathridiids are usually 3-segmented, but in the males of some species, the tarsi of the first pair or first 2 pairs of legs may be 2-segmented. The tarsi of cryptophagids are 5 segmented, except for the males of some species, in which they have 4 segments. Thus, the number of tarsal segments is a good criterion for the separation of the 2 families (Hinton, 1945).
Some Common Species
The beetles shown in figure 332 were among many taken from 2 newly built, plastered apartment buildings in the Los Angeles area. Cartodere constricta is yellowish brown and 1.75 mm long; Aridius nodifer is yellowish brown to pitchy black and 1.9 mm long; Cryptophagus laticollis is reddish yellow and 2.1 mm long; and the cucujid Silvanus bidentatus (F.) (figure 332, D) is cinnamon brown and 3.3 mm long. The latter is a fungus-feeder or scavenger, according to T. J Spilman (correspondence), which was found abundantly in an apartment that was also infested with the lathridiid Aridius nodifer, a few cryptophagid beetles, and a mycetophagid fly, Litargus balteatus LeConte.
The 5 species were collected 3 months after the apartment was plastered.
According to Hickin (1964), 48 species of lathridiids and 80 species of cryptophagids were found in Great Britain. In buildings he checked, the most common lathridiids were Aridius nodifer (Westwood), Thes bergrothi (Reitter), Corticaria serrata (Paykull), and Lathridius minutus (L.). The most common cryptophagids were Cryptophagus acutangulus Gyllenhal, C. cellaris (Scopoli), and C. distinguendus Sturm.
Microgramme filum (Aubé) (= Cartodere) (figure 333) was considered by Hinton (1941) to be the lathridiid most commonly found in buildings in Europe as a whole. It is also distributed throughout North Africa and North and South America.
The adult beetles are 1.2 to 1.6 mm in length, brownish, and have 2-segmented antennal clubs, whereas other species of this genus have 3 segments in the clubs. Hindwings are lacking in all species of Microgramme. Mature larvae of M. filum are 1.7 to 2 mm long, whitish, and have 3 segmented antennae, the second segment twice as long as the first. The pupae are white, and 1 mm long.
Hinton observed that 2 females laid a total of 20 eggs. The shortest life cycle at 75 °F (24 °C) was 36 days. At 65 °F (18 °C), a complete life cycle required about 54 days, and at lower temperatures might take as long as 5 months. The life cycles of 4 lathridiid species investigated in the United States varied from 12.8 to 28 days, and averaged 21.2 days at a mean temperature of 74.6 °F (23.7 °C) (Kerr and McLean, 1956). Microgramme filum was found in such environments as damp, moldy warehouses and cellars; damp areas near water taps; around leaky windows; under moldy wallpaper and moldy papier-mâché dishes; in damp stored wheat, corn, and rye; in boxes containing dried beer yeast; on moldy bread; and in many herbaria. Microgramme arga (Reitter) (= Cartodere) is similar to M. filum, but can be distinguished by having 3 instead of 2 segments in the antennal clubs and by having larger eyes. It is widely distributed, occurring in Europe, North Africa, and North America (Hinton, 1941).
Fungus Beetles Feeding on Moldy Stored Food Products
Henoticus californicus Mannerheim, the California fungus beetle, is a uniformly brownish cryptophagid, about 3 mm long, that is probably indigenous to California, but has spread to various parts of the world through commercial channels. The larvae and adults feed on molds on various food products, and the females oviposit on the food (Linsley and Michelbacher, 1943). It is quite likely that this is one of the so-called "plaster beetles."
Alphitophagus bifasciatus (Say) the twobanded fungus beetle, is a reddish-brown tenebrionid, with 2 wide black bands across the elytra. It is 3 mm long, elongate-oval, and convex. Outdoors it normally feeds on fungi growing on moist trees, but indoors it infests fermenting or decayed cereals and cereal products. It is cosmopolitan in distribution, and occurs in coastal California and Oregon (Essig, 1926).
Alphitobius diaperinus (Panzer), the lesser mealworm (Tenebrionidae) (figure 182, chapter 7) is also attracted to damp and moldy cereal products and spoiled foods. (See chapter 7, under "Insects Infesting Broken Grain," for a few more data.)
Ahasverus advena (Waltl), the foreign grain beetle, is a cosmopolitan cucujid, with projections at the anterior corners of the prothorax. It feeds on molds on damp grains, bread, biscuits, and other farinaceous materials, as well as dead insects that may be found in or on them.
Feeding Habits of Fungus Beetles
In nature, fungus beetles are found in vegetable detritus, under bark and stones, and sometimes in ant and termite nests. The lathridiid Microgramme filum has been observed feeding on the spores of various species of Polysaccum, Ustilago, Arctium, Trichothecium, Lycoperdon, Tilletia, and on the spores and hyphae of fungi in herbaria, where the beetles are often pests. It was also reared on cultures of Mucor mucedo and Penicillium glaucum in petri dishes (Hinton, 1941). Four species - Cartodere constricta, Corticaria serrata, Adistemia watsoni (Wallaston), and Microgramme arga - were reared successfully on mixed cultures of the molds Aspergillus, Mucor, Botrytis, and Penicillium, appearing to prefer Penicillium (Kerr and McLean, 1956). As with the psocids, the lathridiids may feed on fungi developing on stored foods and seeds in damp locations. Associated with such stored products in California are the lathridiids Enicmus minutus (L.), E. suspectus Fall, and Holoparamecus caularum (Aubé), and some widely distributed but undetermined species of cryptophagids (Strong and Okumura, 1958).
Because both the larvae and adults of fungus beetles feed exclusively on the hyphae and spores of molds, mildews, and other fungi, they can exist only under the damp conditions required for fungal growth. They usually appear 3 or 4 months or as long as a year after the walls of a building are plastered, and disappear after the walls are thoroughly dry and can no longer support the growth of molds. Plastered walls are most likely to support an infestation if they are papered, so wallpaper should not be applied until the walls are completely dry. Walls and other parts of a building can also become damp from sources of moisture other than plaster, and can support infestations of fungus beetles or psocids. The beetles cannot crawl on smooth, vertical surfaces, and are often trapped in ceiling light fixtures, washbasins, bathtubs, or pots and pans. Fungus beetles and psocids can sometimes be found on building materials as they are incorporated into the structure, or on wrappings of plumbing and electrical fixtures, but they can also be brought in later on moldy or mildewed furnishings or other materials.
Mallis (1969) reported the lathridiid Microgramme arga from ground cereals in Oregon, on the walls of a house and in a drugstore in Ohio, on heads of wheat in a field in Texas, and in an old brick house in Pennsylvania that had just been remodeled into apartments. The insects were found in June on walls that had been plastered 3 months before the infestation. They were seen around the windows and near a light fixture in the ceiling. The new plaster was apparently not completely dry at the beginning of the infestation, and high humidity caused by heavy rains kept the walls from drying out, thus encouraging the growth of molds. By late summer, the beetles had disappeared.
In Los Angeles, California, lathridiids, cryptophagids, and psocids were found in one plastered apartment building soon after the first apartments were occupied. A few of the beetles could be found in the building as long as a year after its completion. The adults were generally found at lights or windows. In one of the apartments just discussed under the heading, "Some Common Species," 3 months after occupancy, many lathridiids, cucujids, and a few cryptophagids and mycetophagids were collected. The apartment had been sprayed earlier for "plaster beetles," and hundreds had already been killed.
Control of Fungus Beetles
Anything that results in the drying out of the parts of a building that support the growth of molds and mildews upon which fungus beetles subsist, such as a long period of hot, dry weather, can terminate an infestation. (Moldy foods should, of course, be removed.) Artificial heat and ventilation can aid in the drying process. It is of interest in this connection that 98% of adult fungus beetles (Adistemia watsoni) died in 7 days at 100 °F (38 °C), 100% died within 24 hours at 110 °F (43 °C), and at 130, 140, and 150 °F (54, 60 and 66 °C), complete mortality was obtained in 10, 5, and 4 minutes, respectively (Kerr and McLean, 1956).
Fungicides such as Cunilate (copper-18-quinolinolate) and G-4 (dichlorophene) (NPCA, 1957), or 2% formaldehyde in petroleum distillate (Busvine, 1966), can be sprayed onto moldy areas, taking care to avoid contamination of foods. Fumigation of a building is rarely warranted for an existing fungus beetle infestation, since it provides no residual protection against reinfestation. Aerosols are convenient, and may kill the beetles contacted, but not those emerging later from concealed locations. Longer-lasting insecticidal residues can be obtained with sprays containing 2% chlordane, 1% lindane, or 0.5% dieldrin, provided the sprays are applied where the beetles can contact the residues, such as in the vicinity of moldy materials and about lights and windows where they congregate. Wall voids and other places difficult to reach with sprays can be dusted, using 5% chlordane, 1% lindane, or 1% dieldrin, adding 3% G-4 (dichlorophene) if a fungicide is desired in addition. Thorough milling to form a fine dust that will drift well into concealed areas should improve the mixture (NPCA, 1957).
Psocids (order Psocoptera) are small insects, found throughout the world in damp and secluded places in grass, dead leaves and litter under trees and shrubs, damp wood, under lichens and moss, or under bark, where they feed on molds and mildews. At least 2 of the species commonly found in buildings are cosmopolitan pests. Psocids have biting mouthparts, but they cannot bite humans or animals. They are harmless except for the contamination of foods, and are nuisances in the same way as many other insects merely by their presence in a home. These insects are sometimes called "booklice" or "barklice" because of their superficial resemblance to certain species of lice and because they are found, sometimes in very large numbers, on moldy books and papers in damp buildings or their basements and under loose, damp bark. Books are said to be particularly susceptible to mold growth because of the glues and sizes used in binding, upon which molds can develop under damp conditions (Hickin, 1964). Psocids also resemble minute workers of subterranean termites; in fact, psocids and termites, as well as cockroaches, are believed by some investigators to have had a common ancestry.
Psocids are soft-bodied insects, the immature forms of which resemble the adults in form and structure. They are gray or light brown, winged or wingless, with a large abdomen, a narrow thorax, a large head, and long, many-segmented antennae. The outdoor species have wings, but are weak fliers. Their wings are held rooflike over the body, and are often marked with a pattern of some sort. The pearly-white eggs are relatively large, being about one-third the size of the adult insect. They are laid singly, and adhere to the surface upon which they are deposited.
Species Infesting Buildings
Two well-known cosmopolitan species commonly encountered in buildings or as household pests are the cereal psocid, Liposcelis divinatorius (Müller) (Liposcelidae) and the larger pale booklouse, Trogium pulsatorium (L.) (Trogiidae), also known as the "deathwatch." The latter receives its specific name from the ticking sounds it produces by striking its abdomen against paper and similar materials. Only the females make these sounds, believed to be mating calls. Another species, Lepinotus inquilinus (Heyden) (Trogiidae) is believed to be capable of making the same kind of sound (Pearman, 1928). A species of Psyllipsocus (Psyllipsocidae) (figure 334) is sometimes found in buildings in southern California. The cereal psocid and the larger pale booklouse are both wingless indoor species. The latter has small, scalelike wing pads, well-developed compound eyes, and is about 2 mm long. The cereal psocid has no wing pads, only a few scattered simple eyes, and is about 1.5 mm long. Both species can move about very swiftly. Both have soft bodies, and are cream-colored to grayish or light brown. Other psocids reported as household pests are Lachesilla pedicularia (L.) (Lachesillidae); Psyllipsocus ramburii (Selys) and Psocathropos lachlani Ribaga (Psyllipsocidae); Lepinotus patruelis Pearman and L. inquilinus (Heyden) (Trogiidae); and Liposcelis bostrychophilus Badonnel (= granicola Broadhead and Hobby) (Liposcelidae) (Pearman, 1928; Broadhead and Hobby, 1944; Finlayson, 1949; Gurney, 1950).
Psocids can be serious pests of stored foods under excessively humid conditions. A key was developed to help identify 5 species commonly infesting stored foods in the United States: Trogium pulsatorium, the larger pale booklouse, which has 3 distinct thoracic segments (the other 4 species have only 2); Liposcelis bostrychophilus, the banded psocid, which has 7-faceted eyes and a brown head and body; L. paetus Pearman, the warehouse psocid (figure 335), which has 2 to 4-faceted eyes, a brown head, and yellow body; L. entomophilus (Enderlein), the grain psocid, which has 2 to 5 large pronotal bristles; and L. terricolis (Badonnel), the "booklouse" (figure 335), which has only 1 large pronotal bristle. [Liposcelis bostrychophilus and L. paetus do not have large pronotal bristles (Scott, 1963b).]
Biology. The cereal psocid, Liposcelis divinatorius, reproduces parthenogenetically (males are not known). In one investigation, the life cycle averaged 24.4 days from June to August, with an average of 57 eggs deposited. During cold weather, the adults died, and the eggs hatched in the spring. In winter, only 21 eggs per female were produced on an average, the preoviposition period was 45 days, and the life cycle was 110 days (Ghani and Sweetman, 1951). There may be 6 to 8 generations per year (Candura, 1932). In another investigation, the period from egg to adult required about 1 month at a temperature of 80 °F (27 °C) and relative humidity of 65%. There were 3 molts. After a preoviposition period of 2 to 3 weeks, eggs were laid at the rate of about 1 every 12 hours until perhaps 75% of the total were laid. Then, a long period followed when only an occasional egg was deposited. An adult life of over 3 months was observed (Finlayson. 1932). In England, Trogium pulsatorium was found to have only 1 generation a year and to overwinter in the nymphal stage, whereas Liposcelis divinatorius bred continuously, and was found in all stages, even during the winter months (Pearman, 1928).
Influence of Humidity
At humidities near the "critical equilibrium," a decrease in relative humidity of only 5% can result in the decline of a psocid infestation. For example, specimens of Liposcelis rufus Broadhead and Hobby lost water at RH's of 53% or less. At 25 °C (77 °F) and 33% RH, they lost 50% of their water in 11 days, but most of them recovered the lost water within 6 to 7 hours after being transferred to an RH of about 58%. The flat and contracted abdomens of the dehydrated insects became inflated, returning to their original sizes and shapes, when adequately moist air became available.
Desiccated L. divinatorius recovered even more rapidly. Insects that had become flattened and lethargic from desiccation became turgid and active within 2 or 3 hours when moisture was restored, and began laying eggs (Finlayson, 1932). With food available, females of L. rufus died within 2 to 3 weeks at all RH's below 58%. Other species were even less resistant to desiccation. Females of L. knullei Broadhead and Hobby lost water twice as fast as L. rufus, and died within 1 week at all humidities below their critical level. Liposcelis bostrychophilus survived only 10 days, and egg-laying ceased, below the critical equilibrium humidity (Knülle and Spadafora, 1969).
Psocids, like fungus beetles, may be pests primarily for a few months after the completion of a building, before the plastered walls have had time to dry out and while the dampness can support a growth of molds, particularly in wall voids. Psocids may escape from the voids and infest large sections of the living space. They are often most abundant on the top floors of multistoried buildings because they are the last to be plastered and have the greatest variation in temperature - both factors that result in greater dampness (Hartnack, 1943). In a house, psocids occur not only in spaces between walls, under floors, and behind door and window trims, but also in cupboards and closets, behind electrical and other fixtures, in upholstered furniture containing tow or Spanish moss, in rugs, books, paper, groceries, flour, cartons of merchandise, straw matting, and contents of trunks taken from storage, feeding on microscopic molds occurring on such materials if they are damp (Back, 1946). Psocids are sometimes found only in 1 area of a house, such as a room used for drying clothes. The regular use of the room for that purpose may result in a continuous infestation. As with silverfish and fungus beetles, psocids may fall into washtubs, washbasins, pots, or pans and be trapped, for they cannot climb on smooth, vertical surfaces.
After having moved from 2 apartment buildings in succession because of psocid infestations, tenants in a beach community in southern California moved to a third building, but first they had their overstuffed furniture, clothing, blankets, linens, and other personal belongings fumigated to avoid the possibility of a third occurrence of what had become a traumatic experience.
Besides being household pests, psocids resemble fungus beetles in occasionally infesting granaries, warehouses, herbaria, insect collections, libraries, stored foods, and the nests of birds and insects (Finlayson, 1932; Linsley, 1942, 1944; Broadhead and Hobby, 1944). The 2 household pests, Liposcelis divinatorius and Trogium pulsatorium, have been reported as predators of eggs of the Angoumois grain moth, Sitotroga cerealella (Finlayson, 1932), and Liposcelis bostrychophilus was observed to feed on the eggs of the Indian meal moth, Plodia interpunctella (Lovitt and Soderstrom, 1968). In one test, L. bostrychophilus consumed 71 and 72% of the eggs when other food was absent or present, respectively.
Control of Psocids
In general, the foregoing recommendations for control of fungus beetles pertain also to psocids. With either pest, merely waiting for a building to dry out may solve the problem. This solution is more likely to be accepted by homeowners than by rent-paying occupants of an infested house or apartment, especially if they have heard psocids referred to as "booklice."
Mallis (1969) cited the results secured by a pest control operator who thoroughly sprayed, with 2% chlordane in base oil, all the exposed woodwork of a 6-month-old house that had been built with green lumber. He obtained excellent control of psocids. In view of the widely recognized efficacy of dichlorvos, Mallis suggested that a 0.5% solution of this insecticide should also be tried in psocid control.
Springtails (order Collembola) are very small insects, usually less than 2 mm long, and they do not undergo metamorphosis. They are among the most primitive insects, having been identified as fossils from the Devonian period, over 400 million years ago, and thus antedating any other known insect fossils (Jeannel, 1960). According to Scott (1966c), of about 500 species reported from North America, 19 have been noted to infest buildings, of which 10 are shown in figure 336. There are species adapted to every climatic condition high in the Himalayas, in Antarctica, in the intertidal zones of ocean beaches, on the surface of standing water, and in great numbers on snow in winter. They can occur in enormous numbers, for example, up to 50,000 per cu ft (28 cu dm) of forest litter. Most species of springtails lack tracheae, and respire through their cuticles. As might be expected, the cuticles of such species are very permeable to water. Therefore, these insects must spend most of their time in very damp locations. If they find themselves in a dry situation they crawl about actively until a damp environment is found (Joose and Groen, 1970).
Springtails are found outdoors in moist situations, usually feeding on algae, fungi, and decaying vegetable matter. They are among the most troublesome swimming pool pests. In southern California, Hypogastrura armata (Nicolet) (figure 336, E) appears to be the one most frequently involved. This is a common species of world-wide distribution. It is dark gray to black dorsally, light gray ventrally, and with a reddish hue on the head, antennae, and legs.
If their environment becomes dry, then in the course of their active crawling in search of moisture, springtails may invade the home, entering through window screens, open doors, vent pipes, or with merchandise or ornamental plants. They may be attracted to light, entering through windows or under doors. After a hot day, they may swarm over the side of a building in tremendous numbers, increasing the chance of indoor infestation. After entering a house, they crawl about, and are often trapped in sinks, washbasins, and bathtubs. They are most commonly found where there are sources of moisture, as in the kitchen and bathroom, where they hide in very small cracks and crevices. They may also occur in damp wall voids. In some homes, potted plants serve as sources, the springtails coming from the damp soil (Scott et al., 1962; Scott, 1966c).
Ideal conditions for springtails result from high humidity in conjunction with excessive organic debris. In addition to whatever nutritive material that may be present in the organic matter, mildew spores can form, contributing further sustenance. Springtail infestations can be suspected whenever mildew odors are detectable. Infestations tend to increase during hot, humid weather, and decrease during cold weather when the heating system dries the air and the building structure. Even during the drier periods, however, springtails may be found in great abundance around the insulations of steam and water pipes (Scott et al., 1962; Scott, 1966c).
A pictorial key has been prepared to help identify the common springtails of the United States (Scott et al., 1962).
Springtails as Pests
These insects are pests principally by virtue of their presence in the home. They have never been incriminated in the transmission of any human disease, but Entomobrya nivalis L., a cosmopolitan species, has been reported to cause an itching type of dermatitis in man, and Orchesella albosa Guthrie, found in North America and Europe, has been recorded as infesting the head and pubic areas, but without causing dermatitis (Scott et al., 1962). Another cosmopolitan species, Entomobrya atrocinta Schött (figures 336 and 337), is a pest of dried milk powder (Scott, 1963b). Springtails crawling or hopping on the skin may cause itching, and when crushed on the skin, they may cause a mild, localized, allergic response. (Scott et al., 1962; Scott, 1966c).
Control of Springtails
The best control for springtails is to decrease humidity within the building, if possible, and to improve sanitation by not depositing food particles in cracks, crevices, and around floor edges. Large deposits of dust and lint should not be permitted to accumulate anywhere in the building. Moldly bedding, mattresses, couches, and chairs have been found to be good habitats for the pests. Spraying or dusting of infested surfaces, including potted plants, has been found to be effective, using common household insecticides. The plants should be watered only after the soil in the pots appears to be dry. (See also, chapter 11.)
MISCELLANEOUS MITES AND INSECTS
- Grocer's Itch Mite, Glycyphagus domesticus (De Geer) (Acaridae)
- Fungus Gnats (Mycetophilidae)
- Darkwinged Fungus Gnats (Sciaridae)
- Humpbacked Flies (Phoridae)
- Fungus Moth, Aglossa caprealis (Hübner) (Pyralidae)
- Meal Moth, Pyralis farinalis (L.) (Pyralidae)
- Nemapogon sp. (= Tinea) (Tineidae)
- Control of Fungus Moths
Grocer's Itch Mite, Glycyphagus domesticus (De Geer) (Acaridae)
This is a small, white mite found in pantries, feeding on cereals, sugar, cheese, and other foods. and in furniture stuffed with green Algerian fiber, where it feeds on the fungi growing on the fiber. The furniture may become white with myriads of these mites, and they may spread to other parts of the house. According to A. M. Hughes (1961), Algerian fiber and the fiber from which rush furniture is made are highly hygroscopic, taking up and retaining moisture from the air. In a damp environment, molds upon which the mites feed develop on the furniture. Infested, fiber should be removed and the furniture restuffed with some other material. However, anything reducing humidity within a room, such as improved ventilation, will decrease the chances of infestation. Infestation does not occur in furniture constructed of either Algerian fiber or rushes if they have been treated with copper sulfate.
The mold mite, Tyrophagus putrescentiae (Schrank), is becoming increasingly common as a household pest, causing allergic reactions.
The silverfish are described and illustrated in chapter 8, under "Pests of Fabrics and Paper." They seek warmth and moisture, and are sometimes found in large numbers in damp wall voids of newly constructed buildings. Wall voids can be drilled and treated with insecticide dust or fog.
Fungus Gnats (Mycetophilidae)
Description and Biology. Fungus gnats are small, slender, delicate flies that somewhat resemble mosquitoes, and many species are also about the same size as mosquitoes. They are attracted to light, and do not bite. The thorax is relatively large and arched, and the head is small. The antennae are long and filiform, 12 to 17 segmented, but usually with 10 segments, the 2 basal segments being quite large. The coxae are long, the coxae and femora are thickened, and the tibiae have prominent distal spurs and usually a series of short or long bristles. Adults may be black, yellow, brown, red, or a combination of these colors, depending on the species. They are fairly common, and may be seen moving rapidly over dark and damp places where there is an abundance of decaying vegetation or fungi, on which they lay their eggs singly. The eggs hatch within a few days.
The larvae are usually slender, 12 segmented, footless, with 8 pairs of spiracles, smooth and whitish, but with brown or black sclerotized heads. They infest fungi, damp soil, litter, decaying vegetation, or decayed wood. Under optimum conditions, the larvae can develop through all 5 instars in 6 to 8 days. Some species form silken cocoons on or in the ground in which to pupate, and the adults emerge in about 3 days. Certain species are pests in mushroom cellars (Essig, 1926; Lauret, 1962; Curran, 1965).
Fungus Gnats in Homes
Fungus gnats breed in humus, leaves, and litter under shrubbery around the house, and find their way inside. Within the home they breed in pots, boxes, flower vases, and any container in which nouse plants are grown. All household sprays, aerosols, or suspended vapor-releasing strips are effective in controlling them indoors.
Some Common Species
The 2 most common and widely distributed species in the United States are Mycetophila fungorum (De Geer) (= punctata Meigen), a brownish gnat 4 to 6 mm long, and M. ichneumonea Say (= mutica Loew), a very small, reddish yellow or fuscous gnat, 2.7 mm long. In addition to these, in California are found M. contigua Walker (= fallax Loew), 3 to 3.7 mm long and dark brown to black; Mycomyia mendax Johannsen, 6 mm long, yellow and black; and Lela striata (Williston), 5 mm long, with the head and thorax yellow and the abdomen black.
Darkwinged Fungus Gnats (Sciaridae)
Sciarids (figure 338) are closely related to the mycetophilids, but their eyes meet above the bases of the antennae, whereas in the mycetophilids the antennae are inserted on a level with the middles of the eyes. Also, the coxae of the sciarids are not so elongate as those of the mycetophilids The adults are small, usually black, and occur in moist, shady places. The larvae feed on fungi, and those of some species often travel over the ground in snakelike "armies." Some species occasionally become pests in mushroom cellars, while others infest the roots and tubers of plants and cause some injury.
Humpbacked Flies (Phoridae)
The phorids are very small flies that are easily recognized by the small head and prominent pronotum, giving them a humpbacked appearance. Only the veins toward the foremargins of the wings are thickened; the others are weak and are not connected by cross veins. The hind femora are laterally flattened. The dirty-white, slightly flattened larvae are up to 4 mm long. The adults are abundant on and near decaying vegetation. They are attracted to lights in structures and are often a nuisance in houses.
Megaselia rufipes (Meigen) is a cosmopolitan species that is commonly encountered throughout the United States. It is black or dull brown, with yellowish or brown legs.
Megaselia scalaris (Loew) is a tropical and subtropical species and Dohrniphora cornuta (Bigot) is a cosmopolitan species; both are common in California.
Fungus Moth, Aglossa caprealis (Hübner) (Pyralidae)
Certain species of moths develop on the dry-rot fungus (Poria incrassata) (figure 102, chapter 5), on damp straw, or in leaf mold in sufficient numbers to become household pests. Aglossa caprealis can subsist entirely on the dry-rot fungus. It can be readily distinguished from a tineid moth, Nemapogon sp., which has similar habits, but is smaller and more slender. However, A. caprealis could easily be confused with cutworm adults or other moths that accidentally gain entry into a home.
Description. The adult moth is dark brown, with uneven, lighter markings across its broad wings. When at rest, the male measures 13 mm and the female 16 mm in length. The female is 19 or 10 mm across at the tips of the folded wings (figure 339). The mature larva is naked, shiny dark brown to black, and is about 20 mm long. It is ringed with interrupted annulations that give it a wrinkled appearance (Pence and Hogue, 1957).
Habits. This moth occurs in the dark, damp locations where dry-rot fungus develops. In one instance in which the insects originated in mycelial growth of fungus under a sink, where leaky tile grouting permitted moisture to penetrate the wood beneath, the larvae were found in much of the house, but particularly in the kitchen and bathroom, and migrated extensively before pupation. In another instance, this species was found infesting a garage adjoining a home. A pile of damp fabrics stored in the garage had developed a growth of fungus, providing food for the larvae. A laboratory experiment demonstrated that these larvae could thrive on a diet consisting only of the mycelium of Poria incrassata. They fed directly on fragments of dry mycelia placed on a damp substrate. The fragments were bound together in dense webbing (Pence and Hogue, 1957).
Meal Moth, Pyralis farinalis (L.) (Pyralidae)
This moth is found breeding in damp locations, such as in straw, vegetable refuse, or moldy leaves, and it sometimes invades houses. Both this species and Aglossa caprealis were reported from grain under damp conditions (Strong and Okumura, 1958). G. T. Okumura (correspondence) believes that all species of the family Pyralidae, even those found on trees, are to some extent mycetophilic and scavenging, feeding on fungi or on dead and moldy material.
Description. The meal moth has a wingspread of about 25 mm. The base and apex of the forewing are reddish brown, with the middle portion pale, but bordered on each side by a wavy, white line. A row of black dots occurs along the posterior margin. The dirty-gray larva, with a dark head and prothoracic shield, is about 25 mm long when full grown (Linsley and Michelbacher, 1943).
Habits. In one instance, where the moths infested all the rooms of a house and persisted despite attempted control measures, a mass of webbed and matted straw was found on moist soil in the crawl space under the building. The straw was teeming with adults and immature stages. The moths had found their way into the rooms by entering forced-air heating vents and pipe openings.
The infestation stopped after the straw was removed (Berns, 1958).
Nemapogon sp. (= Tinea) (Tineidae)
The forewings of this species are brown, with many black spots (figure 340). The wing markings distinguish it from the various species of clothes moths, for which it is at times mistaken because of its obvious family resemblance. It has been found infesting homes in which the substructure was infected with dry-rot fungus.
In common with Aglossa caprealis, the moth can reach full development on a diet consisting solely of dry-rot fungus (Pence, 1956a).
Control of Fungus Moths
Measures taken to control the dry-rot fungus (chapter 5) will also eliminate infestations of fungus moths. Spraying the infested areas will usually eliminate larvae or adults that are moving about in the living space of a house.
SOWBUGS AND PILLBUGS
Sowbugs and pillbugs (class Crustacea, order Isopods) are said to be indigenous to Europe, and to have been introduced into North America. Hatchett (1947) believed that this accounted for their abundance only around human settlements on this continent.
The commonly used English name, "woodlouse," is more appropriately applied in Europe, where these isopods occur commonly in wooded areas far from human habitations, than it is in North America.
In the United States, sowbugs and pillbugs may be found in and around homes wherever there is a combination of excessive moisture and an abundance of decaying organic matter. The majority of isopods are aquatic forms, and obtain their oxygen through gills, but the sowbugs and pillbugs breathe by means of tubelike invaginations or pseudotracheae, enabling them to live on land. However, the pseudotracheae open to the exterior by a single pore which lacks the spiracular closing device possessed by other arthropods. Some respiration also takes place through the integument of the body (Cloudsley-Thompson, 1968).
These land crustaceans are not so well adapted as insects for controlling water loss, for they not only lack a closing device for the respiratory system but also lack the epicuticular wax layer that protects insects from excessive transpiration, even in dry environments (Edney, 1957; Barnes, 1963; Cloudsley-Thompson, 1968). Therefore, these isopods must remain during the day beneath objects on damp ground, or even bury themselves well beneath the ground, if necessary, to avoid desiccation. They may also huddle together in masses to reduce the evaporation rate, and travel about during the night, taking advantage of the lower temperature and higher humidity. Moist food and water to drink also help to replace the water lost by integumentary evaporation.
Sowbugs and pillbugs normally live outdoors, and sometimes injure tender young plants or their roots. Their scavenging habits are indicated by an observation that pillbugs in large numbers almost completely devoured a dead rat and ate the flesh off a peach pit (Pierce, 1907). They sometimes become accidental intruders into houses, where they do no damage and cannot survive. Slab floors and sliding doors have increased the likelihood of occasional intrusions of these isopods into the home.
Sowbugs, Porcellio laevis Koch and P. scaber (Latreille) (Porcellionidae)
These cosmopolitan sowbugs are the most common species throughout the country. They are often pests in residential properties where there are damp locations in which they can hide during the day, such as under trash, rocks, boards, flower pots, piles of grass clippings, flower-bed mulches, or other decaying vegetation.
Description. Sowbugs (figure 341) are up to 13 mm long, dorsoventrally flattened, oval, and have a broadly convex, hard exoskeleton composed usually of 10 freely articulating tergites that tend to project laterally. The segments of the thorax and abdomen are usually about the same width, and are not clearly demarcated dorsally. The adults are dark gray to slate color above, with a wide, dark, longitudinal median band becoming lighter in color laterally, and they are light gray beneath. They have well-developed, sessile, compound eyes, well-developed antennae, and 7 pairs of legs, a pair for each thoracic segment (Barnes, 1963). Porcellio scaber differs from P. laevis in having transverse rows of small tubercles covering the head and body dorsally (CloudsleyThompson, 1968).
Biology. The eggs hatch in a brood pouch (marsupium). During the last weeks of a gravidity of about 50 days, there may be eggs in the marsupium as well as young sowbugs ready to emerge. In investigations by Hatchett (1947) in Michigan, 24 young per brood were born on an average, but as many as 88 young per brood have actually been recorded (Verhoeff, 1919, 1920). There may be 1, 2, or 3 broods per year, but usually 2 (Hatchett, 1947). Adult sowbugs may live about 2 years.
Pillbug, Armadillidium vulgare (Latreille) (Armadillidiidae)
Pillbugs look somewhat like sowbugs. In the pillbug, the last abdominal appendages, the uropods, are rounded posteriorly, whereas in the sowbugs they project from the hind end of the body like a pair of small, pointed tails. Thus, the uropods can be used to distinguish between pillbugs and sowbugs, as can be seen in figure 341. When pillbugs ar:e disturbed, they roll up into a tight ball, cover the front part of the head with their uropods, and are then, of course, even easier to distinguish from sowbugs than when they are not rolled up.
Biology. The biology and habits of pillbugs are similar to those of sowbugs. Pierce (1907) noted that pillbugs were white and had 6 pairs of legs when they left the marsupium. Within 24 hours they molted, and still had 6 pairs of legs. The next molt occurred between the fourteenth and eighteenth days, and the isopods then had 7 pairs of legs. There was no regularity in the time of molting after the first molt; the time depended on the food supply. Pierce found that females about 7 mm long could reproduce. The largest pillbug he noticed was 15 mm long, and he believed it to be several years old. From 29 to 79 young per brood were recorded in Texas (Pierce, 1907); 5 to 62 (average 28) in Michigan (Hatchett, 1947); and 48 to 156 in France (Vandel, 1939). There could be from 1 to 3 generations per year, depending on the mean temperature of the region.
Control of Sowbugs and Pillbugs
Much can be accomplished toward the control of these crustaceans by eliminating the moist environments that make their terrestrial life possible. Piles of leaves and grass clippings provide both moist hiding places and food, and should be removed. Boxes, boards, flower pots, and trash should be removed if they are lying on damp soil, or they should be stored off the ground. Proper ventilation of the crawl spaces under buildings will eliminate a common source of excessive moisture. An undue amount of watering should be avoided, particularly where there is a dense growth, such as of ivy.
Residual pesticide treatments may be applied to and near foundation walls, to damp areas surrounding or near the building, and to the crawl spaces underneath it. Most of the common garden insecticides, such as carbaryl, chlordane, diazinon, malathion, and propoxur (Baygon), applied as sprays or dusts, are effective. Treatment of peat moss, wood chips, and redwood bark used as mulches in the garden is particularly important. Subsequent sprinkling will carry the insecticide down into the soil where the crustaceans hide. Known points of entry into the home for sowbugs and pillbugs should be sealed off. These pests can not only be killed with household insecticides, but can also be swept or vacuumed away. Most of them will be dead by the time they are discovered for, as already stated, they cannot survive for more than a day or two away from moist areas.
Millipedes (class Diplopods) have high moisture needs, in common with the sowbugs and pillbugs. They feed on both living and decomposing vegetation, and occasionally on dead snails, earthworms, and insects. They may attack growing crops, but seldom in numbers sufficient to need control measures. During periods of drought, they are sometimes forced to attack crops to obtain water. The principal complaint against millipedes is their tendency to invade homes, sometimes in incredible numbers.
Description. Millipedes are long, cylindrical, many-jointed, wormlike arthropods. The mature forms vary from 10 or 15 to 100 mm or more in length. Most of them are blackish or shades of brown, but some species are red, orange, or have mottled patterns. They have 2 body regions. The head has a pair of short, 7 segmented antennae, at least 2 pairs of mouthparts, and usually eyes. In the body, the first segment behind the head bears no legs, while the next 4 segments (the next 3 in a few species) each have 1 pair of legs. All other segments except the last (in some species except the last 2 or 3) have 2 pairs of legs. The segments with 2 pairs of legs are diplosegments, derived from the fusion of originally separate segments. "Spiracles" leading into tracheae open above the coxae. However,.the tracheal system has no closing mechanism such as the spiracles of insects (Miley, 1930). The integument is hard, rounded above, and flattened below. Like the integument of isopods and chilopods, it possesses no protective lipid barrier. The absence of surface lipid, along with the inability to close the tracheal openings, makes diplopods particularly susceptible to a lethal rate of water loss in dry environments.
The two pairs of legs on most segments, particularly well shown in figure 342A, distinguish millipedes from centipedes. Most millipedes are rounded above, whereas centipedes are flattened. Millipedes crawl very slowly, whereas centipedes crawl quite rapidly. However, the gait of millipedes exerts a surprising pushing force, enabling the animals to force their way through humus, leaves, and loose soil (Barnes, 1963).
Biology. Millipedes lay from 20 to 300 eggs in nests in the soil. The eggs of most species hatch in several weeks, and the newly hatched young usually have only the first, 3 pairs of legs and not more than 7 segments. Millipedes have a simple metamorphosis, going through a number of molts during each of which additional segments and legs are added. In many species, there are 7 larval instars. Many species of millipedes reach sexual maturity in 2 years, but some require 4 or 5 and will then live several more years. Adults generally overwinter in the soil. In some orders, the millipedes build molting chambers in the soil, similar to the egg nests, for after each molt the animals are helpless against predators. Millipedes usually eat their cast skins to restore lost supplies of calcium, and if they do not do so, further development is abnormal (Cloudsley-Thompson, 1968).
Protective Devices. Millipedes do not possess venom-bearing claws (toxicognaths) as do centipedes, but they do have certain protective devices. The species of one order of millipedes (Oniscomorpha) can roll up into a ball like the pillbugs, protecting their soft underparts.
In the Colobgnatha, Polydesmoidea, and Juliformia there are repugnatorial glands, either 1 per segment on all but the more anterior segments or on more or less alternate segments. They open on the sides of the tergites, and secrete a mixture of hydrocyanic acid, iodine, and quinone, a brown or white liquid with an iodoform odor. It is believed to be toxic to other small animals, and is reported to be caustic to the human skin and to cause vesicular dermatitis. Most species exude the liquid slowly, but some can discharge it as a spray. Some of the tropical species can produce a severe dermatitis and possibly blindness (Halstead and Ryckman, 1949; Barnes, 1963).
Sometimes millipedes, occasionally accompanied by centipedes and sowbugs, will migrate in great numbers. This is believed to be the result of a heavy buildup of the millipede population because of very favorable environmental conditions, followed by drought (Cloudsley-Thompson, 1949, 1968). Migrations have at times involved such enormous numbers of millipedes as to make it necessary to sprinkle sand on slippery railroad tracks to provide traction for the driving wheels of locomotives. Brooks (1919) described a migration of the millipede "Fontaria virginiensis Drury" (Pleuroloma sp. inc.) in West Virginia in such great numbers that cattle refused to graze on invaded pastures, wells became filled with drowned corpses of the arthropods, and workers in fields became nauseated and dizzy from the odor of millipedes they crushed while hoeing in a cornfield. In another migration of an estimated 65 million millipedes, a farmer shoveled a half bushel or more of these pests from his porch and surrounding area and carried them away every morning for a period of 2 weeks. In another migration of "Fontaria brunnea" in strawberry farms in West Virginia, the millipedes fed on overripe fruit and became so abundant that the picking of the fruit had to be discontinued. Fontaria brunnea Bollman is actually a species or subspecies in the genus Pleuroloma, native to the Minnesota Michigan Iowa region only, casting doubt on the correctness of the identification. All specie's of Pleuroloma seem to have a tendency for great aggregations and "swarming" that is not observed in closely allied genera (R. L. Hoffman, correspondence).
Back (1939) described migrations of millipedes in the eastern United States in which they swarmed over basements and first-floor rooms of houses in great numbers. Sometimes they crawled up walls and dropped from ceilings. These migrations occurred most often in the fall. He considered the migrations to be caused by an urge to seek hibernating quarters, although sometimes heavy rains raised the water level in the soil and forced the millipedes to seek shelter elsewhere. Back found that homes in wooded areas with virgin soil, still filled with quantities of decaying vegetation, were particularly susceptible to infestation. As many as 700 millipedes entered a room in a single evening.
Many millipedes, as well as sowbugs and pillbugs, drop into swimming pools, and are usually more common problems in this respect than are insects. Also, sliding doors in houses with concrete slab foundations allow the entry of many millipedes, centipedes, sowbugs, and pillbugs.
Some Species Common Around Structures
The 2 millipede species found by Bennett and Kerr (1973) to be the greatest nuisances around buildings were the greenhouse millipede, Oxidus gracilis (Koch) (= Orthomorpha), and Orthomorpha coarctata (Saussure), particularly the latter, although it is found only in the southern half of Florida. Oxidus gracilis is widespread throughout the southern and western United States in the open, and in greenhouses elsewhere. The millipedes shown in figure 343 were found in large numbers congregated under flower pots in commercial orchid glasshouses in the Los Angeles area.
Description. Oxidus gracilis is one of the "flatbacked" millipedes (order Polydesmoidea), in which the somites are dorsoventrally flattened. The 20 postcephalic somites bear 30 and 31 pairs of legs in the males and females, respectively. The adult males are about 19 mm long, and the females, about 21 mm. These millipedes vary in color from the creamy white of recently molted specimens to deep chestnut brown or black in the oldest individuals (Causey, 1943).
Orthomorpha coarctata is almost indistinguishable from Oxidus gracilis. Two other species common in California are Julus hesperus Chamberlin and Tylobolus claremontus Chamberlin (figure 342, A and B).
Life Cycle. As with most tropical animals, Oxidus gracilis has no annual breeding season. Oviposition was found to occur during any month of the year if the temperature was maintained above 22° C (71° F). Eggs were deposited in small, rough cavities, 7 to 15 mm below the soil surface, in clutches, that varied from 14 to approximately 300. The larvae of each instar differed in the numbers of somites and legs, in size, and in density of pigmentation. Sexual maturity was reached in the eighth instar. Five millipedes reared from eggs collected in September passed through the 7 larval instars in 148 to 177 days at "heated-room" temperatures (Causey, 1943).
Orthomorpha coarctata laid eggs in the soil in holes that were 20 to 40 mm deep and 5 to 7 mm in diameter. There were 25 to 300 eggs per clutch. The.period from egg to adult ranged from 119 to 187 days in a rearing room. There were apparently 2 generations per year (Bennett and Kerr, 1973).
Habits. In the limited areas where 0rthomorpha occurs, it is a greater problem than Oxidus. It apparently breeds in the thick thatches of St. Augustine grass (Stenotaphrum secundatum) in southern Florida that contain large amounts of decaying organic matter on which it feeds. The greatest migration activity was observed from about 8 to 11 in the forenoon, but very little occurred in the afternoon hours until sunset. Migration activity about one-third of that noted in midmorning continued throughout the night, from 10 p.m. to 7 a.m. The millipedes were commonly observed on patios, outside walls, and foundations of buildings. Their numbers increased during the summer and fall months, and reached pest levels from late September to early December (Bennett and Kerr, 1973).
Oxidus gracilis appeared to breed only in wild and overgrown areas where there was much decaying leaf litter. From these places, it occasionally dispersed to nearby habitations. It fed on decaying organic matter, but could not be induced to feed on tender, living plants (Causey, 1943; Bennett and Kerr, 1973).
Control of Millipedes
Decaying vegetation and other favorable harborages should be removed, and insecticides should be applied in the same manner as that recommended for the control of sowbugs and pillbugs. Control appears to be effective with practically any of the currently popular insecticides at the concentrations most commonly used for the control of garden insects, applied as liquid sprays, dusts, or granules. Granules (for example, 5% carbaryl or 10% diazinon) are convenient to use, and will filter down through turf to the soil surface better than dusts. Homer (1967) recommended a spray of 1 % carbaryl or 2% chlordane, applied to the soil around the foundation wall, in addition to a 5 or 10% dust of carbaryl or chlordane in a strip 10 to 15 ft (3 to 4.5 m) wide around the house. Millipedes were not controlled indoors with either space sprays or baits, but sprays or dusts of carbaryl, chlordane, or diazinon were usually effective. Bennett and Kerr (1973) found 3 carbamates (carbaryl, methomyl, and propoxur) to be the most effective among the many pesticides they tested. They all gave a 100% kill in 4 to 5 hours.
The centipedes (class Chilopoda) are the fourth and last of the obligatory dwellers in very moist environments to be considered in this chapter. Like the millipedes, they are long, narrow, and many-segmented, but are nearly always flattened. Their antennae are much longer and have many more segments than those of the millipedes, and they also differ in never having more than 1 pair of legs per abdominal segment (figure 342, C). As with the sowbugs, pillbugs, and millipedes, centipedes, are nocturnal, and do not have the impervious, cuticular wax layer that is characteristic of insects (Cloudsley-Thompson, 1954). They always live in damp, dark, secluded places, such as under boards, stones, piles of leaves or litter, under logs, or under bark and in crevices in damp soil. Most species are carnivorous, but others will sometimes feed on plant tissues, and may occasionally be injurious to crops. They can be accidental intruders into homes, just as with the millipedes. Since they are mostly carnivorous, they are able to obtain their moisture requirements to some extent by feeding on the live insects they can capture. Also, they crawl more rapidly than millipedes and sowbugs, and are more likely to find sources of moisture. They are thus able to survive in buildings for much longer periods. Because they have venom-bearing claws (toxicognaths), centipedes are more fully treated in chapter 9.
Fig. 332. Fungus beetles. Lathridiidae: A, Cartodere constricta; B, Aridius nodifer. Cryptophagidae: C, Cryptophagus laticollis. Cucujidae: D, Silvanus bidentatus.
Fig. 333. A fungus beetle, Microgramme filum. A, larva; B, pupa; C, adult. (From Hinton, 1941.)
Fig. 334. A house-infesting psocid, Psyllipsocus sp.
Fig. 335. Two psocids commonly found on stored foods under excessively humid conditions. Left, warehouse psocid, Liposcelis paetus; right, booklouse, Liposcelis terricolis. (From Scott, 1963b.)
Fig. 336. Building-infesting springtails. A, Onychiurus armatus Tullberg; B, Isotomodes tenuis Folsom; C, Folsomia sp.; D, Proistoma sp.; E, Hypogastrura armata (Nicolet); F, Lepidocyrtus sp.; G, Entomobrya atrocinta Schött; H, Orchesella sp.; I, Seira platani (Nicolet); J, Podura aquatica L. (From Scott, 1966c.)
Fig. 337. Two springtails commonly found in damp locations in and around buildings. Top, Onychiurus armatus; botton, Entomobyra atrocinta.
Fig. 338. A sciarid fly occasionally found in damp locations in buildings.
Fig. 339. A pyralid fungus moth, Aglossa caprealis. Adult and larva.
Fig. 340. A tineid fungus moth, Nemapogon sp.
Fig. 341. Isopods that may invade the home. Top sowbugs, Porcellio dilatatus; bottom, pillbugs, Armadillidium vulgare.
Fig. 342. A, millipede, Julus hesperus; B, millipede, Tylobolus claremontus; C, centipede, Scolopendra polymorpha.
Fig. 343. The greenhouse millipede, Oxidus gracilis.