Within the last 15 years, psocids have emerged as a serious stored-product pest, accountable for a 40 percent increase in problems in Australia, which was one of the first countries to see the disturbing increase. While the U.S. has not yet noted such astronomical rates, the lack of information on the reason for the emergence is concerning and has lead to numerous research studies.
Read more about psocids and their impact on food plants in “Pserious Psocids.”
Some facts that are known and are contributing to psocid recognition as a serious global pest are:
- In countries such as Australia, psocids have gone from causing less than 1 percent of the stored-product pest problem to now causing more than 40 percent of the problem in some parts of the country
- Psocid germ and endosperm consumption has caused weight losses in grains of up to 10 percent, while studies of cake mixture have revealed that psocids to cause 52 percent weight reduction over a period of 16 months.
- Because psocids deteriorate commodities by their presence (live and dead specimens, excrement) and their distribution of molds, they are recognized as a health hazard.
- Heavy psocid infestations, which appear like moving brown carpets on surfaces, can cause allergic reactions in some, while others may experience discomfort from psocids crawling on them.
- Heavy infestations can also become a serious safety hazard because of slippery conditions created.
- Standard pest protection practices and disinfestation frequently fail to control psocids.
- Commodities infested by psocids can be rejected for export.
- Like other storage pests, psocids can cause indirect losses by increasing grain temperature and moisture content and spreading fungal spores
- Psocid presence can increase the reproductive of rate of red and confused flour beetles which feed on psocid eggs.
Source: Compiled by Oklahoma State University Assistant Professor George Opit.
Psocid Biology
Booklice or psocids belong to the order Psocoptera, the ptera referring to “wing” and the psoc referring to the chewing mouthparts of these insects (Arnett 2000). The number of species of psocids found in North America varies depending upon the authority consulted. Most entomological texts use Roesler’s (1944) classification that recognizes 11 families and 150 species, whereas Arnett (2000) identifies 287 species from 28 families. Most psocids are outdoor inhabitants, winged as adults, and commonly found on the bark of trees and shrubs, thus giving them the common name of barklice. Several genera and species seem to specialize in dwelling around human buildings and food storage areas are often called booklice. Booklice psocids are extremely flattened and are common around cracks and crevices, as well as in the bindings of moldy books.
Booklice range from 1/25 to 1/13 of an inch (1 to 2 millimeter) in length while some outdoor, winged barklouse species may be as large as ¼ inch (7 millimeter). The coloration of booklice ranges from almost colorless to gray or light brown. Psocids have long, filamentous antennae and a characteristic bulging clypeus (the area just above the mouthparts). They have chewing mouthparts, and the wings of some home-infesting species are usually absent or reduced to small scales.
COMMON PSOCID SPECIES. The most commonly encountered genera, Liposcelis and Lepinotus, are flattened into the typical booklouse shape. Although some taxonomic confusion exists in the literature related to the species in those genera, about 20 species may be found in home, factories and in stored foods. Mockford (1991) listed in an identification key about 50 species of psocids associated with stored foods or houses worldwide. The following Liposcelis are most commonly listed: cereal psocid, L. divinatorius (Muller); booklouse, L.corrodens Heymons (=L.terricolis); banded psocid, L. bostrychophilus Bandonnel (=L. granicola); warehouse psocid, L. paetus Pearman; and grain psocid , L.entomophilus (Enderlein). Lepinotus inquilinus Heyden is also common in houses as is the larger pale trogiid (or “deathwatch” psocid), Trogium pulsatorium (Linnaeus). Both are more robust in body shape and both have been known to drum their abdomens on loose paper which makes a distinct ticking sound. The reticulated winged trogiid, Lepinotus reticulatus Enderlein, and the cosmopolitan grain psocid, Lachesilla pedicularia (Linneaus), are common in stored grains as well as buildings.
DEVELOPMENT AND BEHAVIOR. All representatives of this order undergo maturation from egg to adult through a simple or paurometabolous metamorphosis. All members have wing tissues present, but most “indoor species” do not develop full, functional wings. The cereal psocid, as well as other species, commonly reproduces parthenogenetically (without mating), as males have not been observed. Other species, however, even in the same genus, may have both males and females. The larger pale trogiid not only reproduces sexually, but the female actually use sound to attract a mater (Pearman 1928a).
Many psocids occur outdoors, on or under bark, grass, leaves, damp wood, and similar places. These outdoor species are often referred to as “barklice.” Some semitropical psocids spin webbing on tree trunks or outside house walls, especially where lichens grow, and are a nuisance in Gulf Coast states (Mockford 1957). Broadhead and Hobby (1944) noted that a presence of booklice has been recorded from houses, warehouses, herbaria, insect collections, libraries and in stored foods. Psocids prefer damp, warm, undisturbed situations. They become most numerous in houses during the spring and summer but are less numerous during winter, likely due to lower temperatures and humidity.
Psocids, for the most part, feed upon microscopic molds. Thus, any manufactured material of plant origin that would support the growth of these molds would also encourage infestation by booklice. Psocids have been observed, however, feeding on starchy food, apparently foraging upon both the starch source itself and any molds present, including the starchy paste and glue of book bindings and wallpaper. Finlayson (1932) observed them in large numbers in soft wheat where they fed upon the eggs of the Angoumois grain moth, Sitotroga cerealella (Olivier).
A number of records exist where these insects have become extremely abundant in old-fashioned straw mattresses and made life unbearable by creeping over the walls, food, cupboards and throughout the house. The author was consulted concerning an insect infestation in a warehouse in Laredo, Texas, where psocids were breeding prolifically in two pallets of bagged oats intended for use in a school lunch program. Piles of dead psocids, literally inches deep, were found in between bags of oats and on the floor oats had been stored in the non-air conditioned, humid warehouse for more than one year, which allowed such a population explosion to occur.
Newly constructed buildings are not immune to infestations of booklice. Sudden “blooms” of psocids are possible even within the first few weeks of finishing construction. It is believed the moisture of the plaster and the sizing used to apply wallpaper to some walls as well as moisture trapped within walls prompts fungus growth, thus allowing the survival of booklice.
Psocids can be readily introduced to new structures on building materials, as well as upon furniture, boxes, books and paper. Once inside the building, they will be found on the walls, in cupboards where they can invade cereals and sugar, behind moldings and baseboards, in wall voids, behind electrical outlets, and sometimes upon the wrappings of electrical or plumbing, air conditioning elements and ducts.
Although psocids may become extremely annoying by crawling over everything in the house and contaminating foodstuffs by their presence, they usually cause negligible damage to commodities. Back (1939b) stated that much of the damage attributed to psocids should actually be charged to silverfish and cockroaches.
Source: Mallis Handbook of Pest Control