Coleoptera
Beetles are the most diverse order of insects, with around 30,000 species. They have two pairs of wings, chewing mouthparts and undergo complete metamorphosis. Species associated with stored foodstuffs generally measure less than 1 cm.
Pest beetle larvae are elongated, white or pale yellow, with a head, a legged thorax and an abdomen often with urogomphae. Unlike caterpillars, they have no false abdominal legs.
In addition to direct feeding damage, these insects can cause grain to heat up, accumulate moisture and deteriorate grain quality by promoting the proliferation of fungi and bacteria. Larvae generally cause more damage than adults
Lepidoptera (butterflies)
The order Lepidoptera, which includes butterflies, includes many species that are active both day and night. In North America, some 11,000 species have been identified, including 4,700 in Canada. Species harmful to stored goods are exclusively nocturnal, measuring less than 3 cm in length and 4 cm in wingspan. As adults, they have two pairs of wings covered with scales, often dull in color, in shades of gray or brown. Their mouthparts are adapted for sucking. Like beetles, they undergo a complete metamorphosis. The caterpillars, or larvae, of these pest species are generally elongated and whitish, with a distinct head capsule, developed mandibles, eyes and antennae. The thorax bears three pairs of segmented legs, and the abdomen generally has seven pairs of fleshy false legs with hooks. Caterpillars use their thoracic legs to move, and their false legs to grip and maintain their balance. Many caterpillars produce silk with their mouthparts, forming a silk mat on stored grain. Adults do not cause direct damage to grain, but they do seek out these commodities to mate and lay their eggs.
Psocoptera (psoques)
The order Psocoptera comprises a limited number of species, with around 340 recorded. Psocoptera are very small insects, generally measuring less than 6 mm in length. Their soft bodies can be brown, gray, yellow or whitish. Their wings, membranous and functional only in adulthood, vary according to species: well-developed, short or absent. They have long antennae and crusher-type mouthparts with well-developed mandibles. Omnivorous, psoques feed on mold, grain dust and dead insect fragments. Their metamorphosis is incomplete, involving three stages: egg, larva and adult. Psoques can reach very high densities in the absence of predators and parasitoids, causing deterioration of stored grain and staining it with their droppings. Because of their small size, they are often mistaken for mites.
Acariens
Mites, belonging to the Arachnid class, number around 1,900 species in Canada. They are tiny, giving the impression that infested foodstuffs are covered in dust. Their oval bodies are poorly differentiated. Metamorphosis is incomplete, with larvae having three or four pairs of legs and adults four. Most species are brilliant white.