Australia

Brown wheat mite

Petrobia latens

Brown wheat mites are metallic brown to black, and about the size of a period in ordinary newspaper print. Their legs are pale yellow, and their forelegs are distinctively longer than the other three pair of legs. Females of the brown wheat mite are known to lay two types of eggs. Both types of eggs are laid on soil particles near infested plants. During the winter, females lay nearly spherical, cherry red eggs that can hatch in a week with favorable weather. In the spring, females lay white eggs with a waxy coating and a ruffled cap that do not hatch until fall. No one female can lay both types of eggs.

Damage: BWM moves from the soil to thehost plant to feed. Feeding produces afine stippling that causes leaves to take on a water-stressed appearance, turning first dusty gray and then yellow. Infested wheat or barley plants appear scorched or bronzed and withered, attributes that can easily be confused with drought symptoms. Brown wheat mites feed on plant sap during the day and spend the night in the soil. Their activity peaks at about midafternoon on warm, calm daysóthe best time to monitor. This mite is not affected by cold temperatures, but populations are dramatically reduced by increased humidity or by being washed from the plant by driving rains or irrigation. Mites are difficult to monitor because of their small size, lack of webbing and habit of dropping from the host plant to the soil when disturbed.