by Mike Potter, Extension Entomologist
University of Kentucky College of Agriculture
The foreign grain beetle is a common pest in Kentucky during mid- to late summer and is often found in tremendous numbers inside buildings.
The beetles are very small (about 1/16-inch long) and reddish brown. Foreign grain beetles belong to the same family as the sawtoothed grain beetle and are similar in size, but can be identified from this insect by the lack of "sawtoothed" projections on the pronotum (segment directly behind the head). The key characteristic to look for in identifying the foreign grain beetle is the presence of a slight projection or knob on each front corner of the pronotum. A microscope or good quality hand lens is necessary to see this character.
Foreign grain beetles are frequently problems in new houses, but not normally in association with grain and other stored products. These beetles are one of a group of beetles called "fungus beetles" that feed on the molds and fungi that grow on poorly seasoned lumber or wet plaster and wall board. If they are found infesting stored products, the products generally are moldy or in poor condition.
When new homes are built, damp wood is often covered with molds or mildew which attracts the beetles. The beetles may also be attracted to accumulations of sawdust which often occur behind walls as a byproduct of construction. Eggs are laid on this food material and the larvae develop on the surface fungi. The adults usually become a problem in late summer when they move out of wall voids and are attracted to windows and lights. Foreign grain beetles can also be associated with plumbing leaks, condensation problems, or poor ventilation.
Control is best accomplished by drying out the wood and/or eliminating the moisture source. Most new homes dry out naturally within the first few years, and the fungi and molds disappear along with the beetles. Drying time can be enhanced by increasing ventilation, e.g., by use of fans and air conditioning. Rapid relief can be obtained with directed applications of aerosol sprays containing pyrethrins, but such treatments must be applied frequently. A vacuum cleaner works just as well in terms of removing any visible beetles which are present. More permanent control can be achieved by locating the infested wall areas or source of dampness (usually next to where the beetles are most abundant) and injecting residual aerosols or dusts into cracks and crevices along baseboards and into the wall voids.
If the homeowner can tolerate the beetles during the period when they are most active (late summer) the problem will usually resolve itself. Some comfort can be taken in the fact that foreign grain beetles are only a nuisance by their presence, i.e., they do not bite or damage wood, fabric or stored food in sound condition.
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!