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Spruce Sawfly Emerging (06/09/16)

Adults of the yellowheaded spruce sawfly are being observed (June 1st) on spruces in shelterbelts in Eddy County.

Spruce Sawfly Emerging

Adults of the yellowheaded spruce sawfly are being observed (June 1st) on spruces in shelterbelts in Eddy County (Source: Emily Goff, NDSU Agent-in-Training, Eddy, Foster and Wells Counties). Watch for larvae (caterpillars) that will be emerging in 5-10 days and feeding on spruce needles, especially in the tops of trees. Larvae can cause severe defoliation. If insecticidal sprays are necessary, they are directed at young small larvae, not the adult sawfly.

Adult sawflies are not flies but stingless wasps. The insect is called a sawfly because the female's ovipositor has serrated teeth resembling a wood saw. There is one generation per year. Adults are reddish-brown in color and are about 8 mm long. From late May through mid-June, adults emerge from overwintered pupae and mate. Females begin laying eggs, with a single egg deposited at the base of a needle. Eggs hatch in five to ten days. Young larvae are about 5 mm long and mature larvae are almost 2 cm long and are dark glossy green with a light lateral stripe and reddish-brown head. Larvae feed for 30 to 40 days, consuming new foliage first and then older needles. Mature larvae drop to the ground to pupate.

Defoliation is caused by larval feeding. Heavily infested trees appear ragged, especially near the top, and can be completely stripped of foliage. Severe infestations over one to several years can kill trees directly or make trees susceptible to attack by other insects.

Open-grown trees that are five to nine years old are more vulnerable to yellowheaded spruce sawfly damage than are older trees or trees in dense stands. Predators, such as birds and rodents, and parasitic wasps are not always effective in keeping sawfly populations at acceptable levels. If infestations are light, larvae can be removed by hand for small number of trees in yards. Homeowners also can remove larvae by spraying with a strong jet of water. However, chemical control often becomes necessary as the sawfly population increases, especially for shelterbelts with large number of trees.

Acephate, bifenthrin, carbaryl, cyfluthrin, lambda-cyhalothrin, malathion and permethrin are labeled for use against yellowheaded spruce sawfly. Biorational pesticides include azadirachtin, horticultural oil, insecticidal soap, pyrethrin and spinosad.

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Janet J. Knodel

Extension Entomologist

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