Introduced Pine Sawfly
Diprion similis

The introduced pine sawfly occurs from Canada to North Carolina, and in the central and lake states. Eastern white pine is its favored host, but it also attacks Scotch, red,jack, and Swiss mountain pines. Infestations of this insect can be very serious in young plantations of white pine grown for timber products or Christmas trees.

Identification:

A full-grown larva is about 1 inch (25 mm) long, with a shiny, black head. The body has a black stripe on the back and numerous yellow and white spots on the sides. Larvae spin light brown, tough, leathery cocoons on the host tree, other vegetation, and ground litter. Adults resemble flies and are about 3/10 inch (8 mm) long and have four transparent wings.

Injury:

Defoliation first occurs in the upper crown, giving it a thin appearance. First generation larvae feed on old needles, and later generations feed on both old and new needles, and sometimes on the bark of twigs. Trees in the most exposed locations and in the overstory suffer the most defoliation. Repeated heavy defoliation can cause branch and even tree mortality.

Biology and History:

Two generations occur each year and sometimes part of a third, resulting in overlapping generations. Late instar larvae overwinter in cocoons and adults emerge in the spring. Eggs are laid in May and early June and hatch two weeks later. Young larvae feed gregariously; older larvae singly. Cocoons are spun during July and August. Second generation larvae feed through September before spinning their cocoon. Others complete development and begin the third generation in the fall, and thus emerge the following spring as mid-instar larvae.