European pine sawfly has hatched throughout the state. At this time of year, they appear as 1/4-inch-long olive larvae with large black heads. They feed in groups on the needles of various pines, particularly Scotch and mugo pine. Older larvae grow to slightly over 1 inch long, are olive with dark green stripes, and also have large black heads. The larvae strip the needles, leaving only the central brown core of the needle, which dries and falls off.
There is only one generation per year, and the larvae are finishing their feeding by the time needles emerge from the candles. Thus, these needles are not damaged, and little threat of branch or tree death results from this sawfly’s feeding. However, the loss of the second- and third-year-old needles is noticeable on landscape trees and devastating to the appearance of Christmas trees. In late spring, the larvae drop from the tree. They pupate in debris under the tree and emerge later as wasplike adults to lay eggs in the needles before winter.
Although these larvae resemble caterpillars, they are actually larvae of insects related to wasps. Because they are not true caterpillars, Bacillus thuringiensis kurstaki (Dipel, Thuricide) is not effective against them. Manage these insects by hand removal or spraying the affected foliage with carbaryl (Sevin), acephate (Orthene), azadirachtin (Azatin, Neem), spinosad (Conserve), or chlorpyrifos (Dursban).