Grain mite
Acarus siro

Order: Acarina
Family: Acaridae
Acronym: ACO

Ecology

Grain mites are found throughout the temperate regions of the world. They feed on stored foods such as flour, grain, seeds and bulbs or on the fungi that develop on these products. They can subsist on organic debris in cracks, crevices and corners of storage areas.

Damage

Grain mites can be classified into two types – forage and predatory. Forage mites feed on grain kernels, germ, screenings and fungi. Predatory mites feed on other mites as well as insect eggs and larvae, and develop only when their hosts are available. Flour mites are forage mites that feed mainly on the germ, but can consume the total endosperm of the kernel.

Life history

Mites are whitish and about the size of a pinhead. They have translucent, soft bodies, with no pronounced demarcation between body parts. Under optimum conditions, a female flour mite may lay 250 eggs in a month, while the female of some species of mold mites can produce as many as 20,000 offspring in the same period. The young mites have six legs, but after molting become eight-legged adults. Under unfavorable conditions, mites enter a non-feeding but highly resistant stage known as the hypopus, in which they may remain for months without food. When conditions become favorable to their growth, they molt and again become active. Because of their soft skin, mites are sensitive to variations in the relative humidity of the air and to changes in the moisture content of the grain. The optimum relative humidity for development is between 80 and 90%.

Control

The best way to control an infestation is to turn the binned grain several times, a practice that will kill most of the mites or dry the grain. Fumigation is ineffective because of the unusual ability of mites to survive under adverse conditions. Aerating grain after harvesting will help to keep an infestation in check. In addition, bins should be cleaned and treated with an approved structural insecticide.

Images

Darwing of a grain mite.

Grain mites.

Grain mites in grain.