Sawflies are members of the insect order Hymenoptera that includes ants, bees, and wasps. The larval stage has a caterpillar-like body that may be brightly marked with stripes or spots. Some species change significantly in appearance as they grow, making identification confusing. Large numbers of sawflies can strip the needles from a tree in a short period. Several species feed on pines in Kentucky.
The introduced pine sawfly (Figure 1) has a black head and black body that is covered with yellow and white spots. They prefer the needles of eastern white pine but also will eat Scotch, red, Austrian, jack, and Swiss mountain pine. It will feed on short leaf and Virginia pines but damage usually is not heavy.
Feeding is most severe in the crown to upper half of the tree but heavily infested trees can be completely defoliated. If this occurs after the winter buds have formed, many branches or even the entire tree can be killed. There are two generations each year. The second generation of this sawfly feeds on both old and new needles during August and September.
The redheaded pine sawfly (Figure 2) prefers two and three needled pines, Scotch, jack, shortleaf, loblolly, slash, red, mugho. Small larvae feed on the surface leaving tan, straw-like needles. Larger sawflies consume the entire needle.
Sawfly populations are usually controlled by combinations of natural enemies, predators, starvation, disease, or unfavorable weather. Outbreaks can occur when natural control does not produce high mortality. Regular inspection of pines will help to detect sawfly infestations before the larvae reach a size that can cause significant defoliation. Since eggs are laid in clusters, feeding by groups of larvae can cause unsightly damage to ornamental or landscape plantings, as well as nursery trees
If only a small number of colonies are present and accessible, they can be handpicked, shaken off, or pruned from the tree and destroyed. Some of the insecticides that can be used for sawfly control are listed by the common name of the active ingredient followed by an example brand name. Acephate – Orthene Turf, Tree & Ornamental Spray; bifenthrin- Ortho MAX Lawn & Garden Insect Killer; carbaryl – Sevin; cyfluthrin – Bayer Multi-Insect Killer Concentrate; permethrin – Ortho Tree, Shrub, and Lawn Spray; and spinosad -Captain Jack’s Dead Bug Brew. Although sawflies look like caterpillars, they are not susceptible to Bt sprays.
By Lee Townsend, Extension Entomologist