Wheat Stem Sawfly

species: cephus cinctus norton
common names: wheat stem sawfly
hosts:
notes:

Agriculture and Agri-Food Canada Insect Identification Sheet No. 19 1976

Wheat Stem Sawfly

Cephus cinctus Norton

The wheat stem sawfly occurs in Western Canada where it can cause serious losses to grains, especially wheat.

Injury:

Damage is caused by the larvae, which tunnel through the stems and later girdle them close to the ground before harvest. Tunneling reduces grain yield and quality, and girdling causes heads to fall to the ground where they may germinate in wet weather or may not be picked up at harvest.

Life History:

The adult wheat stem sawfly is a shiny black, wasp like insect about 8 to 13 mm (1/3 to 1/2 in.) long, with yellow abdominal bands, smoke-colored wings, and yellow legs. Adults emerge during mid-June to early July from stubble fields and native grasses. The adult female lays up to 50 eggs in immature wheat by thrusting its sawlike ovipositor into the stems. There is usually one egg per stem, although several females may oviposit into the same stem. Eggs are crescent shaped, glassy, milky white, and about 1 to 1.25 mm (1/25 in.) long. They hatch in 1 week into pale yellow, S-shaped, brown-headed, wrinkled-bodied, worm-like larvae with a short projection at the tail end. Larvae feed on the pith of the stems, growing to a length of 8 to 13 mm (1 /3 to 1/2 in.) in about 2 months. There is only one surviving larva per stem. In August, it cuts the stem near the base of the plant about ground level, plugs the exposed end and prepares to overwinter in the stubble by building, just below the cut, a long thin brown transparent cocoon. Pupation occurs in May of the next year after a period of 3 months at 10 OC. The pupa is slender and about 12 mm (1 /2 in.) long. The adults emerge from the upper end of the stub. Usually, there is one generation per year although a generation can last 2 years as very high springtime temperatures can force the larvae back into the resting stage.

Pest Management:

Resistant, solid-stemmed varieties of wheat, or immune crops such as oats or fall rye, offer the best means of controlling the wheat stem sawfly. Most varieties of barley are resistant. Early swathing will reduce losses in infested susceptible crops.