Eastern Forest Threat Center - Introduced Pine Sawfly

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Adult male introduced pine sawfly

Adult male introduced pine sawfly

John Ghent, USDA Forest Service, Bugwood.org

Introduced Pine Sawfly
Diprion similis

The introduced pine sawfly occurs from Canada to North Carolina, and in the central and lake states. Infestations of this insect can be very serious in young plantations of white pine grown for timber products or Christmas trees.

Keywords: Hymenoptera, pine trees, four transparent wings, egg rows, yellow and white spots on larvae, leathery cocoons, defoliation, branch and tree mortality

Distribution Map Distribution Source Image

Threat Description

In the southern Appalachians, first generation adults emerge in early spring. Adults resemble flies and are about 3/10 in. long with four transparent wings. Eggs are laid in rows in the pine needles and covered with a light green substance, hatching in about 14 days. A full-grown larva is about 1 in. long with a black stripe on its back, numerous yellow and white spots on its sides, and a shiny, black head. First generation larvae feed on old needles, and later generations feed on both old and new needles, and sometimes on the bark of twigs. Larvae spin light brown, tough, leathery cocoons on the host tree, other vegetation, and ground litter. Larvae feed until cocoons are spun in late June through July. Second generation adults emerge in late July, and most larvae have finished feeding and spin cocoons by late September. Eastern white pine is the introduced pine sawfly’s favored host, but it also attacks Scotch, red, jack, and Swiss mountain pines. Defoliation first occurs in the upper crown, giving it a thin appearance. Trees in the most exposed locations and in the overstory suffer the most defoliation. Repeated heavy defoliation can cause branch and even tree mortality.