Pine Sawflies
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.
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.
Identifying sawflies and their larvae is crucial for monitoring and managing potential infestations. Here are the key characteristics to help you recognize these pests:
Adult Sawflies
- Appearance: Adult sawflies resemble small, stout-bodied wasps. They are often mistaken for flies due to their size and shape but lack the narrow "waist" typical of true wasps.
- Coloration: Depending on the species, adults may range in color from black to reddish-brown, with some having yellow or white markings.
- Wings: They have two pairs of transparent wings with prominent veins, unlike true flies, which have only one pair of wings.
- Egg-Laying Appendage: Female sawflies possess a saw-like ovipositor, which they use to cut into pine needles and deposit their eggs.
Sawfly Larvae
Sawfly larvae are often mistaken for caterpillars (the larvae of moths and butterflies). However, they can be distinguished by the following:
- Legs: Sawfly larvae have more than five pairs of prolegs (fleshy, leg-like structures) on their abdomen, while caterpillars typically have five or fewer.
- Head: They have a well-defined, rounded head that is often a different color than their body.
- Movement: Unlike caterpillars, sawfly larvae do not move in a "looping" motion.
- Color and Patterns: Larvae vary in color depending on the species but often have distinctive patterns, such as stripes or spots, in shades of green, yellow, black, or red.
- Feeding Behavior: Sawfly larvae feed in groups, often stripping needles from branches in a uniform pattern, leaving behind bare twigs.
Signs of Infestation
- Defoliation: Look for clusters of defoliated pine needles, particularly on young trees or lower branches.
- Egg Scars: Female sawflies leave small slits or scars on pine needles where eggs have been deposited.
- Larval Clusters: Groups of larvae feeding together are a telltale sign of sawfly activity.
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.
