The caterpillar-like larvae of the introduced pine sawfly prefer to feed on needles of eastern white pine but also will feed on Scotch, red, Austrian, jack, and Swiss mountain pine. They may feed on short leaf and Virginia pines, but usually damage is not heavy.
Defoliation is most severe in the crown and upper half of the tree, but there can be complete defoliation if there are many sawflies. If this occurs after the winter buds have formed, many branches, or even the entire tree, can be killed (Figure 1). Scattered heavy infestations were reported last fall in Central Kentucky with concern about the potential for continued damage in 2017.
Introduced pine sawflies spend winter inside brown silken cocoons attached to ground debris, tree trunks, or most any other surface (Figure 2). During this time, small mammals or birds consume many. Surviving adults emerge in spring to mate and lay eggs for the first of two annual generations.
There are two generations of the introduced pine sawfly each year. Larvae (Figure 3) of the first generation feed on needles from the previous year. Young sawflies eat the more tender outer parts of the needles while older larvae consume them entirely. They are full-grown (about 1-inch-long) in July. The second generation of this sawfly feeds on both old and new needles during August and September.
Degree Day Accumulations as a Tool to Predict Sawfly Activity
Last year’s significant late-season defoliation does not guarantee problems in 2017, but trees should be watched for early signs of sawfly attack. Degree day accumulations can let you know when to assess infestations. First generation larvae should appear at the accumulation of 400 degree days base 50. You can determine the accumulated degree days for your area at the Calculating Degree Days website:
- Select <Degree Days for Ornamental/Horticultural Insects> from the left-hand menu.
- Select your <County> from the drop down menu.
- Select <Base 50> from that drop-down menu.
There numerous choices of insecticides, including neem products (azadirachtin), spinosad insecticides (Conserve), or pyrethroids – bifenthrin, permethrin, etc.
By Lee Townsend, Extension Entomologist