Foreign grain beetles, Ahasverus advena (Waltl), are particularly common structural pests in late August and early September as cool weather and rainfall increase. Adults are reddish-brown in color, about 1/12-inch long and have a three-segmented antennal club. The distinguishing characteristic of this insect (seen under magnification) is the presence of a tiny knob or bump on each of the front corners of the thorax.
Not as their name may imply, foreign grain beetles are actually fungus-feeding insects. They are normally pests of warehouses and storage facilities where moldy grain or bins are found. Foreign grain beetles also are nuisance pests of newly built strucutres that have moist and decaying lumber (some people call them “new house bugs”). Pallets made of new/green lumber provide perfect conditions for the growth of wood-decaying fungi or molds; consequently, these beetles can be found inside wrapped, non-food grade items.
Furthermore, these bugs also are capable of infesting older buildings with mold, decaying organic matter or rotten stored products. The unusual presence of these beetles indoors in late summer or early fall, as adult beetles move from the field seeking protected places to spend the winter, prompts complaints of infestations.
Once indoors, this pest doesn’t bite or cause damage to any structure, but it is a potential reservoir of pathogenic organisms, such as salmonella. Additionally, it may generate concerns with auditors in food-processing or food-handling plants.
Foreign grain beetles are tropical, strong flyers and attracted to lights. Their life cycle lasts two to four weeks, depending on the temperature and relative humidity (RH) conditions. No reproduction occurs at temperatures less than 59°F nor at less than 65 percent RH with temperatures less than 77°F. At 80-90°F, eggs hatch in four to five days. The larval stage lasts about 15 days and the pupa stage lasts four to seven days. Adults live up to 250 days.
Pest management. A successful management plan begins with eliminating moisture problems that promote fungal/mold growth, which this pest thrives upon. Therefore, clients should remove moisture sources and improve air circulation systems in the infested areas. Remove all decaying and greasy matter from drains, equipment legs, motor housings, electric conduits, bins and other locations as appropriate. Exclude newly introduced beetles by screening doors, windows, and entry points and keeping them closed and well sealed.
Where applicable, and at temperatures above 59°F, use insect light traps to help monitor flying adults and pinpoint the infested hot spots. Insecticide treatments are not a decisive solution as newly emerging adults can come from remote voids, raising the need for frequent treatments. Before treatment, try to locate breeding sources, especially in damp and moist areas. Use properly labeled EPA residual insecticides in cracks, crevices, voids and for spot treatments. Dust formulations are preferred for crack, crevice and void applications, however, approved aerosol insecticides with proper tips are applicable for these treatments. Inaccessible and infested voids are subject to wood replacement or drilling.
Apply a residual liquid insecticide as a spot treatment around light fixtures, attics, crawlspaces, vent openings, around ceiling fans and where insects are seen. Spot treatments with residual dust formulations under the edges of all carpets and baseboards are recommended.
The author is technical training director for Adam’s Pest Control, Minneapolis, Minn. Contact him via e-mail at firstname.lastname@example.org.