Believed to have originated in the eastern Mediterranean region, this weevil is now worldwide in occurrence, particularly in the cooler regions of the world. In the U.S. it tends to be more common in the northern half of the country.
The granary weevil cannot fly, and therefore it has evolved to rely on human transport for its mode of dissemination, and in fact is rarely found in field grains anymore, but almost entirely within products in storage in human structures. It is not a major pest in homes, although it also infests acorns, and could be traced to that source if wild animals were storing them. This is an internal feeder, with the larvae obligated to develop only within a whole, enclosed seed or grain, such as corn, wheat, rice, etc. The female lays around 200 eggs into, placing them one at a time into a small hole she has bored in a grain. She then covers the hole with a film of gelatinous fluid. Larval development lasts about one month, the pupa stage about 10 days, and adults may live up to 8 months. There can be as many as 4 generations each year if conditions are favorable for development.
Weevils are distinguished by the long “snout” coming from the front of the head, with a pair of chewing mandibles at the tip. Their antennae are distinctly bent or “elbowed” about half way out, and they arise from in front of the eyes on the snout. The important food pest weevils are tiny insects, only about 1/8 inch long, and they are dark brownish black. The granary weevil is slightly larger than the rice weevil, has a much shinier appearance due to the less porous exoskeleton, and it is a uniform dark brown, having no light patches on the top of the elytra.
Characteristics Important in Control:
Inspection to determine the location of infested products is important, and usually disposal of this infested material is done. Fumigation with methyl bromide or aluminum phosphide is routinely done to ensure clean, uninfested product is put into storage in commercial facilities. Monitoring with pheromone traps will help to determine if adult activity is beginning.