Foreign Grain Beetle

Common Name: Foreign grain beetle
Scientific Name: Ahasverus advena

Introduction. The common name of grain beetle probably comes from this beetle's association with grains, and that of foreign possibly because at the time of its discovery it was recognized as being an introduced species. Although occasionally abundant, the foreign grain beetle is of minor economic importance because it is a pest of damp and deteriorating stored product materials. The foreign grain beetle is found worldwide and throughout the United States.

Recognition. Adult foreign grain beetles are 1/8 inch long and have a flat body that is uniformly reddish-brown.
Mature larvae are 1/8 inch long, yellowish white, elongate, and are relatively smooth bodied.
Similar Beetles. Mold beetles and plaster beetles (family Lathridiidae) and silken fungus beetles (family Cryptophagidae) are similar in size to foreign grain beetles and maybe found in like habitats. Due to the small size and similarity, identification should be left to an entomologist or pest management professional.

Biology. Adult female foreign grain beetles lay their eggs singly or occasionally in clusters of 2 to 3. Females can lay 100 to 300 eggs over 135 days. Eggs require 4 days to hatch. Larval development takes 11 to 19 days for 4 to 5 instars (growth stages). There is a prepupal period of 1 to 2 days and the pupa stage lasts 3 to 5 days. The development time (egg to adult) requires 17 to 24 days in warm, humid conditions.

Habits. Foreign grain beetles are scavengers, feeding on plant and animal debris and the fungi which grows on such materials. It is attracted to damp and moldy grains where it feeds on the grain, fungi (e.g., Absidia, Aspergillus, Penicillium, Rhizopus, and Streptomyces species), and dead insects and mites associated with the grain.
It is frequently associated with the sheetrock of newly built homes, similar to mold/plaster beetles (Lathrididae). The excessive moisture needed for mold growth comes from rainfall and dew absorbed by the exposed stacks of sheetrock, chipboard and plywood during construction and from the striping and skim plaster coats during the finishing stage. This beetle can also be associated with mold in bathrooms, supported by plumbing leaks or pipe condensation. In both cases, infestations are possible because the adults are very strong fliers and are attracted to lights at night. In the case of bathrooms, a window is frequently left open to let out the excessive moisture after a shower, and these beetles can then enter through ordinary window screens.

Cultural Control & Preventative Measures. Cereal and grain products can be protected from mold growth by storage under dry conditions and can be protected from insect infestation by placing them in thick-walled, airtight plastic or glass containers.
New homes and older homes that support mold growth should be dried to 60% relative humidity through the use of dehumidifiers, improved ventilation / air movement (especially in basements, crawl spaces and attics) and/or air conditioning. Structural and plumbing leaks should be repaired and sound landscaping practices should be observed to reduce outside sources of moisture. A small, hand-held vacuum cleaner can be used to remove beetles that enter living spaces.

Professional Control. A Rottler pest management professional will search for possible sources of moisture and mold-infested beetle breeding sites within the structure. The technician can reduce numbers of foreign grain beetles that enter living spaces by injecting insecticide aerosol or dust formulations into bath traps and structural voids suspected being moldy breeding sites. However, such measures will yield only temporary results if dampness persists.