The eggs of European pine sawfly, Neodiprion sertifer, have hatched throughout Illinois. Young larvae are 1/4 inch long and olive green, with a black head. Older larvae are over 1 inch long, with green stripes. The larvae are gregarious, or feed in groups. They feed on the needles of a variety of pines, especially Scotch, red, and mugo pine. Larvae strip the needles of mature foliage, leaving only the central core, which is white and then turns brown, eventually falling off. Larvae generally finish feeding by the time needles emerge from the candelabra. As a result, those needles are not damaged. There is minimal threat of branch or tree death resulting from sawfly feeding. However, the loss of second- and third-year needles may be noticeable on landscape trees and ruin the appearance of Christmas trees. In late spring, the larvae drop to the ground and pupate in brown, leathery cocoons at the base of trees. Wasplike adults emerge in the fall and lay eggs in the needles before winter. The females create yellow scars in needles when laying eggs. There is one generation per year in Illinois.

Although sawfly larvae resemble caterpillars (order: Lepidoptera), they are the larvae of insects related to wasps (order: Hymenoptera). This means that the bacterial insecticide, Bacillus thuringiensis kurstaki (Dipel and Thuricide), is not effective in controlling sawfly.

Management of European pine sawfly may involve hand removal (if feasible) or washing larvae off plants with a hard stream of water. If necessary, a number of pest-control materials may be applied to affected foliage, including acephate (Orthene), azadirachtin (Azatin or Ornazin), carbaryl (Sevin), chlorpyrifos (Dursban), and/or spinosad (Conserve). When using any pest-control material, be sure to follow label directions.