Squarenecked Grain Beetle
Like other members if the beetle Family Cucujidae, the squarenecked grain beetle is a flat beetle – a necessary shape for hiding in small cracks and under items. It is oblong, reddish brown in color with shiny, polished appearance. It grows to a length of 1/10 inch (2.5 mm) so it is fairly small. Except for its lighter color, upon first glance, it could resemble another common cucujid beetle, the sawtoothed grain beetle. The squarenecked grain beetle derives its name from the unique shape of its prothorax which is sharply rectangular and has points at all four corners. The sawtoothed grain beetle has several tooth-like projections along both lateral sides of the prothorax.

Biology & Life Cycle

The squarenecked grain beetle is found throughout the world and is primarily a pest of corn in the field and in storage. The larvae are external feeders that attack and eat only the germ portion of corn kernels and so a single larva is capable of causing damage to large numbers of kernels and rendering seed corn unfit for germination. In corn fields, adult beetles fly to invade corn ears, particularly those which are damaged. Many infestation of stored corn likely begin in the field.

The life cycle from egg to adult can be as little as three weeks. The development of squarenecked grain beetles is probably similar to that of its close relatives, the sawtoothed and merchant grain beetles.


Because the squarenecked grain beetle is usually associated with whole or cracked corn, inspections should be directed at storage bins and bags where these are stored. Examine grain for the presence of adult beetles and use a screen, if available, to filter the adults and larvae out of the grain to determine their presence.

Inspect the outside of bags stored on pallets and look in between the flaps for adult beetles hiding there. Lift or move bags to look for beetles within the pallet. If numerous beetles are found outside bags of grain, a grain probe can be used to remove grain from the bags for inspection. Bags may also be opened, with permission from the customer to check the extent of the infestation.

These beetles will most often be found infesting larger quantities of corn storage in bins, silos, grain elevators and in bags in warehouses. If smaller packages or quantities of infested grain are involved, the grain can be discarded and the cracks in the area where the infested grain was stored treated with residual insecticides. Small packages of grain can also be frozen for six days at –18°C to kill all life stages.

Empty corn storage bins and silos often are not cleaned properly and can be left empty for considerable periods of time. Large numbers of various grain insects, including squarenecked grain beetles, can be develop in the corn kernels left behind and can infest other storage facilities and nearby buildings. In this situation, the bin must be cleaned as much as possible and the storage bin treated with an appropriately labeled residual insecticide prior to new grain being stored in that facility.

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