The adult is a wasp-like insect that is rarely seen. The larva has a black head, a green body with light and dark stripes.
Larvae hatch in early May from overwintering eggs that were laid in crescent shaped slits in the needles of conifers. Nearly all species of pine may be attacked, including Scots, Mugho, Red, Jack and Swiss Mountain. They begin to feed on old foliage and usually consume only the epidermis of the needles, leaving the core to dry and remain attached. The larvae are gregarious and feed in groups. For protection, they will rear their heads when disturbed. Larvae are found from early May to mid June and then drop to the ground to spin a small brown cocoon. There is usually one generation per year.
European pine sawflies can be quite destructive. Although they usually feed only on old foliage, repeated attack from year to year may lead to stress and decline and reduced tree vitality. If sawflies destroy all the old foliage they may also begin to feed on the newly formed needles of current season's growth. Repeated defoliation can lead to death since most conifers rarely re-leaf. Attacked branches have a tufted appearance and may lose their ornamental value.
Non-chemical: Handpicking the larvae is effective. Inspect all conifers in early to mid-spring for groups of hatching larvae.
Chemical: The microbial insecticide Bacillus thurengiensis(Bt) is not effective against sawfly larvae. Contact your county Extension office for current pesticide controls.