Grain Mite

species: petrobia latens
common names: brown wheat mite
hosts: grasses, wheat
notes:

Agriculture and Agri-Food Canada Insect Identification Sheet No. 79 March 1981

Grain Mites

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.

Injury:

Grain mites can be classified into two types — forage and parasitic. Forage mites feed on whole kernels, germ, screenings and fungi. Parasitic mites feed on other mites as well as insect eggs and larvae, and develop only when their hosts are available. The flour mite, a forage type, feeds mainly on the germ, but occasionally reduces the kernels to hulls.

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 arial, 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. In winter, an infestation can be controlled by cooling the grain to -7 degrees. For full details on mite control, consult your provincial agricultural representative.

Brown Wheat Mite, Petrobia latens (Muller)

Populations build up quickly in hot, dry weather, particularly where irrigation has been neglected.

Vegetables Attacked:

Onion

Injury:

Mite-feeding causes the plants to become pale and mottled. heavily damaged plants look greyish. Mite Adults are minute, shiny, and dark brown. They move quick and are difficult to see. Two types of eggs are laid: active and inactive or diapause eggs. There are one larval and two nymphal stages. Nymphs are similar to adults.

Life History:

The brown wheat mite overwinters in the egg stage Diapause eggs are laid in the fall and overwinter. Active eggs are laid in the summer and take about 10 days to hatch. The larval and nymphal instars have a rest period between each stage. A generation is produced in about three weeks. Mite populations on a plant vary throughout the day. Populations are highest in the morning and evening when temperatures are in the range of 21 to 27C.

Control:

Sprays should be applied when damage is first seen and the presence of mites confirmed.