Get SMART about foreign grain beetle control

The foreign grain beetle (Ahasverus advena) is frequently found in stored products like peanuts, rice and oil seeds — and seems to be a growing topic of conversation among pest management professionals looking to identify, control and prevent them. Despite its common name, the beetle is native to North America and measures about 0.5 inches long. It is often mistaken for a variety of other pests, such as flour (Tribolium spp.), drugstore (Stegobium paniceum) or cigarette beetle (Lasioderma serricorne) species.

It is identifiable by the slight projections on the front corners of the pronotum and its club-shaped antennae. While it mainly feeds on moldy or decaying materials, it can also reproduce on non-moldy foods under certain conditions. Woodroffe (1962) found that foreign grain beetles thrive on rolled oats and dried yeast at 77 degrees Fahrenheit and 65 percent relative humidity (RH) or higher, and can breed on groundnuts at 70 percent RH. Their success diminishes on oilseeds without mold. In structures, these beetles pose a problem as their reproduction relies on moldy conditions or specific additives.

Understanding the development of foreign grain beetles is crucial for effective management. These beetles undergo complete metamorphosis, transitioning through egg, larval, pupal and adult stages. Menter and Mills (1975) found that under optimal conditions of 75 percent RH and 80 degrees Fahrenheit, beetles develop from egg to adult in about 22.5 days. They typically go through 4 or 5 larval stages, with the prepupal and pupal stages lasting 1-2 and 3-5 days, respectively. Mated beetles live for 159-208 days, while unmated ones can live up to 275-301 days. Jacob (1996) found that development times varied widely with temperature and humidity, ranging from 16 days at 30 and 90 percent RH to 70 days at 63.5 degrees Fahrenheit and 90 percent RH. Longevity also varied significantly, with beetles living longer under high humidity and lower temperatures. Jacob’s study highlighted that productivity was high at 80 percent and 90 percent RH, particularly at moderate temperatures, while it was low under cooler, drier conditions.

These beetles often infest newly constructed buildings with damp or decaying materials. In the Midwest, for instance, a new home experienced a significant beetle population that took three years to decline as the materials naturally dried out. Additionally, in this region, they are frequently observed in various buildings from late July through early October, coinciding with their tendency to seek sheltered locations for overwintering (based on personal observations and pest identification request data).

SMART strategies for grain beetle control

Seal entry points. Prevent beetles from entering by properly screening, sealing and maintaining doors, windows and other potential entry points. Regularly inspect for gaps or cracks and ensure they are well-sealed, as these small beetles can enter through even tiny holes.

Monitor activity. Use insect light traps (ILTs) at temperatures above 59 degrees Fahrenheit to track beetle populations, monitor activity and identify infested areas. This helps assess the extent of the infestation and the effectiveness of control measures.

Address moisture. Collaborate with builders to manage moisture in newly constructed homes. Employ dehumidifiers, ventilation systems and heating to reduce moisture content in walls and apply waterproofing treatments and moisture barriers. Tackle indoor moisture issues that support fungal and mold growth by removing moisture sources, improving air circulation, and thoroughly cleaning areas such as drains and equipment. Locate and remove moldy grains and other moldy items on which beetles feed.

Remove and clean. Thoroughly clean and remove decaying or greasy materials from drains, equipment legs, motor housings, electric conduits and bins. Ensure that moldy grains and other items are addressed to eliminate breeding sites.

Treat with precision:

• Preventive treatments: During late summer and early fall, apply exterior pesticide treatments similar to those used for fall-invading pests like boxelder bugs (Boisea spp.) and harlequin lady beetles (Harmonia axyridis). Concentrate on wall sidings and common entry points such as windows, doors, vents and rooflines, with particular attention to the west and south sides (sunlit areas).
• Curative treatments: In newly constructed homes, insecticide application alone may be insufficient due to the ongoing emergence of adults from hidden voids and the difficulty in locating the precise extent of the infestation. It is essential to first identify and address breeding sources, particularly in damp or moist areas. Use appropriately labeled residual insecticides for spot treatments and cracks, crevices and voids. Choose dust formulations that resist moisture and apply aerosol insecticides with the appropriate tips as needed. In cases where voids are inaccessible, wood replacement or drilling may be necessary. Apply residual liquid insecticides around light fixtures, attics, crawlspaces, vent openings and other common beetle harborage sites. Spot treatments with residual dust formulations under carpets and baseboards also can aid overall management.

Conclusion

Managing foreign grain beetles requires a multifaceted approach. Start with accurate identification and address structural and moisture issues to reduce favorable conditions for beetle growth. Implement exclusion methods to block entry, use vacuuming to manage beetles found indoors, and apply targeted pesticide treatments for preventive and breeding source control. Consistently monitor beetle activity to adapt your strategies. By combining these tactics, you can effectively reduce infestations and safeguard your environment.