Wheat stem sawfly (Cephus cinctus), Hymenoptera

Wheat stem sawfly biology & life cycle

This pest is native to North America and lives in grasses. Cultivated hosts include wheat, barley, rye and triticale. Spring wheat is probably the most heavily attacked crop. Plant age is important to the egg-laying female wasps; i.e., plants must be in the jointing (stem elongation) stage for the females to lay eggs. Females lay one egg per stem and the eggs hatch in one week. Larvae feed for two months within the stem boring through the joints. By the time wheat heads begin to ripen, the sawfly larvae have fed within the stem and burrowed down to or below ground level. In August, the larva move upward and cut through the stem about 3/4 inch above the ground, seal the end above them, spin cocoons in the stem and pass winter as larvae in diapause (hibernation). Overwintering larvae pupate within the cocoons in May, and adults emerge in June from the stubble fields and native grasses. There is one generation per year.

Identifying Wheat stem sawfly

Wheat stem sawfly: larvae

Pale yellow with a wrinkled body. Mature larvae are 13 mm long, cream to pale brown, with a brown head. Larval feeding reduces the yield of the crop and lowers the quality of the grain harvested. Larvae also cut the stems in the fall prior to overwintering and this may cause the stems to lodge.

Wheat stem sawfly: Pupae

Found in the bases of the stubble, 12 mm long, slender and pale brown.

Wheat stem sawfly: adult

Shiny black, wasp-like insects 8-13 mmm in length; three yellow bands on the abdomen; wings are smoky and the legs are yellow.

Wheat stem sawfly: management

Plants and stubble should be inspected in the fall for the presence of grass or sawdust at the base of the plants indicating presence of larvae.