Stored Grain Insects



Foreign grain beetle

Ahasverus advena



Adult foreign grain beetle (Ahasverus advena)
Courtesy of CSIRO Division of Entomology

The adult foreign grain beetle (Ahasverus advena) is light brown and about 2 mm long. They are similar in appearance to the saw-tooth grain beetle, however they lack the tooth-like projections and are somewhat broader. Their distinguishing feature is the presence of conspicuous lobes at the front corners of the prothorax.The antennae are slender except for the last three segments, which are distinctly enlarged. The adults are long lived, fly well and run very rapidly. Larvae are initially white and gradually darken as they mature. They rarely grow larger than 3 mm and have no forked process at the tip of the abdomen.


Adult foreign grain beetle (Ahasverus advena)
Agriculture Western Australia

Life cycle
Adult females begin laying eggs around 3 - 4 days after emerging. Most oviposition bouts last 20 - 30 days and alternate with periods during which no eggs are laid (5-23 days). Daily oviposition rates are 1 - 4 eggs but can be as high as 8 - 12 eggs. Peak oviposition occurs 15 days post emergence and 90 - 105 days post emergence. Eggs, which are laid singly or in clusters of two or three, hatch in 4 - 5 days. Larval development is completed in 11 - 19 days. When ready to pupate, the larva constructs a chamber of food particles cemented together. It then attaches itself to the substrate with a brownish substance from the anal aperture. Pupation occurs after a prepupal period of 1 - 2 days, and adults emerge 3 - 5 days later. Humidity is very important to the survival of this beetle. Low humidities are unsuitable for both larval development and oviposition. Larval development times increase with decreasing humidity so that the mean period from egg to adult increases from 19 days at 92% rh to 24 days at 66% rh. Humidity has little effect on the egg, prepupal or pupal stages. Most larvae have 4 instars, however, as humidity decreases, the proportion with 5 instars increase. Oviposition is also effected by humidity; at 75% rh 1.5 eggs/day are laid while at 58% rh the rate diminishes to 0.1 egg/day.The insects do not breed when the relative humidity is below 65% in most foods; in some foods this is true below 80%. Mated males and females have an average lifespan of 159 and 208 days, respectively. Unmated beetles live considerable longer (males 275 days and females 301 days).
This species occurs on a wide variety of foodstuffs, including grains, cereal products, oilseeds and their products, dried fruit, and spices. It is a scavenger that feeds on molds, dead insects, and damaged foods. On cereal grains, the embryo is a suitable food material. However, when found in large numbers they are probably feeding on molds present in the food. Foreign grain beetles have been reared on pure cultures of certain molds commonly found in grains and are considered a good indicator of damp storage conditions.The presence of this insect in farm-stored grain is taken as a warning that the grain is beginning to spoil and become moldy. It is frequently associated with hot spots in farm-stored grain. Although primarily a fungivorous species, it also feeds on various other foods, especially if they are damp and moldy.
Control is best accomplished by drying out the infested material and/or eliminating the moisture source. 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 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. 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.