NOW is the time to be checking pine trees for needle feeding damage by the larvae of the European pine sawfly. Pine sawfly larvae can be present any time after mid-May. The small larvae can only chew the edge from the needle, but as they grown, they consume more and more of the needle until eventually they are eating the entire needle down to the stub. Defoliation lasts for four to five weeks and usually peaks near the end of May. European pine sawfly defoliation is common on Scot, Mugho and Austrian pines, though other pine species may be damaged. The feeding activity causes the old needles to disappear, resulting in isolated bare, branches with tufts of new growth at the end.
Damage is highly variable from tree to tree and from branch to branch within the same tree.
European pine sawfly larvae are grayish-green with 2 light stripes and 1 dark stripe on each side of the body. The legs and head are shiny black. Full grown larvae, usually present by Memorial Day weekend, are about 1 inch long. A curious but distinctive characteristic is that the larvae are gregarious and stay together in a cluster as they feed, moving as a group from one stipped branch to the next. Pine sawfly larvae feed only on old needles that emerged in previous seasons and not on the new needles that are emerging now.