There are over 100 species of sawflies in the U.S. whose larvae feed on the foliage of conifers; several occur in Tennessee including introduced pine sawfly (Diprion similis), redheaded pine sawfly (Neodiprion lecontei), and European pine sawfly (Neodiprion sertifer). Sawflies are not actually flies (Order Diptera), but rather they are a type of non-stinging wasp (Order Hymenoptera). They are called sawflies because they resemble flies and have a saw-like appendage that protrudes from their abdomen which is used to insert eggs into pine needles. Sawfly larvae are potentially serious defoliators of many pine species in Tennessee; heavy defoliation can lead to growth loss or mortality. Outbreaks of this pest generally do not warrant control measures, but sawfly activity should be closely monitored to prevent serious damage. This pest is most common in young plantings, but trees of all ages may be attacked.
Symptoms include defoliation. Early larval instars feed only on the outer edges of needles; partially consumed needles will turn brown and fall off and resemble fine straw hanging from the tree. Older larvae will consume the entire needle. Complete defoliation of pines is possible during severe outbreaks.
Fully grown larvae are easy to identify; the larvae is approximately 1 inch long, pale to bright yellow, have four to six rows of black spots on the body, and a prominent red head. Larvae often cluster together to feed. Adults are rarely seen and resemble flies that are approximately 1⁄4 inch long with four clear wings.
Usually not required. Severe infestations usually subside naturally after 1 or 2 years, but populations of this pest should be monitored to avoid serious damage. Rapid population declines are usually due to predation by rodents, birds, and a viral disease that spreads rapidly through large populations. Chemical control options are available but are only effective against early instars. Because generations overlap considerably, larvae at all stages of development are usually present making successful treatment difficult. Often, by the time severe defoliation is detected it is too late to apply insecticides. The best option is to wait until the following year, monitor the new population, and treat early in the growing season if necessary.