Bad Bugs: Psocids

By Alain VanRyckeghem, BCE
Technical Director

The psocids (SO-sids) found in food/grain storage or food manufacturing facilities are soft bodied insects, 1-2 mm (1/16 inch) long. They have slender antennae, chewing mouthparts and may have four wings or be wingless. They are generally gray or brown in color. Psocids are readily identified (under magnification) by the presence of a large, noticeable bulge where we might call a nose (clypeus). Their hind femurs are characteristically enlarged and flattened.

Life Cycle
There are four species of wingless psocids that are cosmopolitan and may be seen commonly in buildings, usually Liposcelis spp. Psocids are not harmful to people or pets; they cannot bite or sting and are pests only by being present. Psocids can however, produce significant weight and quality loss in grains (up to 10%). They selectively feed on the germ of broken or damaged kernels.

Eggs are one-third the size of the adult, are ovoid in shape, glistening, translucent, and glued to the substrate or deposited into crevices. The average development from egg
to adult takes 18 days at 32.5°C (90°F). Adults live for up to 90 days, and produce a maximum 75 eggs during that time.

Biology and Behavior
Infestations of psocids are more likely in commodities with high moisture content which have mold growth. Psocids feed most commonly on molds as well as fungi, grains, insect fragments, and other starchy material. Flour and other farinaceous (powdery) products are
the foods most frequently found to be infested. Residual layers of powdery food dust, wood (e.g. pallets) or paper packaging (e.g. stitched bags, cardboard) can provide a substrate for mold growth. Psocids will also attack insect collections and other museum exhibits.

In structures, they can be found in damp, warm, undisturbed and poorly vented locations where mold and fungi are growing. In cases where there is no air handling/management system, an entire warehouse and its contents can be conducive for mold growth. They
are more likely to be a problem during middle to late summer when humidity increases significantly. They are rarely damaging inside buildings but they can become a serious pest because of their presence, especially when they occur around processed food ingredients, food packaging or finished products.

Monitoring and Control
There are no specific devices with pheromone for monitoring psocids. Flat glue traps or blunder traps are sufficient to detect their presence. In grain facilities cardboard refuges
can be very useful to pick up psocid activity. Visit the ARS USDA site below for more information.

In structures, the most effective method for controlling booklice is to reduce moisture. Most psocids do not survive when humidity falls below 50%. A dehumidifier or fan is effective in reducing moisture. Sometimes air movement may be sufficient. Also repair any moisture problems and store boxes, bags, books, and papers off the floor to minimize exposure to dampness. Sanitation is also a key element in the management of psocids in food facilities.

In commodities, grain protectants and fumigants are the most common choices. Some psocid species are resistant to residual insecticides and the fumigant phosphine, while others are not. L. bostrychophila, L. entomophila, and L. decolor are grain storage pests. L. bostryichophia shows the greatest resistance to phosphine, but the least resistance to the organophosphate and pyrethroid grain protectants. It is important to identify the species found in grains as it can have importance on selection of control strategy or dosage rates of fumigant.

This USDA site has an excellent picture key to help identify psocids. It has links to the most recent research done by George Opit, James Throne, and Paul Flinn. Other information on biology and management of psocids in the United States can be found on this site.



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