Sawflies – Late Season Pine Defoliators

Sawflies are members of the same 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 needles from a tree in a short period.

Insect Description & Damage

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. Shortleaf and Virginia pines have been attacked but usually are not heavily damaged.

Figure 1. The introduced pine sawfly caused locally significant damage last fall (Photo: Lee Townsend, UK)

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.

Management

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 Houseplant & Garden Insect Killer
  • carbaryl – Sevin
  • cyfluthrin – Bayer Multi-Insect Killer Concentrate
  • esfenvalerate – Ortho Garden & Landscape Insect Killer Concentrate
  • permethrin – Ortho Tree, Shrub,, and Lawn Spray.

Although sawflies look like caterpillars, they are not susceptible to Bt sprays.

 

By Lee Townsend, Extension Entomologist

 

 

Posted in Landscape Trees & Shrubs