Sawflies are a diverse group of insects in the order Hymenoptera, which includes the ants, wasps and bees. The females of this group of non-stinging wasps have a saw-like blade (ovipositor) at the tip of their abdomen that is used to cut slits into plant tissue to deposit their eggs. Sawfly larvae feed on a variety of coniferous and broadleaf trees and shrubs and are among the only members of Hymenoptera that feed on plants. The larvae look like the caterpillars of butterflies and moths, but may have more than five pairs of prolegs (foliage feeders) or may have no legs at all (stem borers). Pine sawflies belong to a group known as conifer sawflies (Diprionidae) and may cause severe defoliation of pine trees. When defoliation occurs in the fall, pine trees may not have enough time to grow new needles in the same growing season. The resulting loss in vigor may make the trees more susceptible to damage by extreme weather conditions and other pests such as bark beetles and other wood boring insects.
Of the 36 pine species that occur in the United States, 7 species are found in Texas. The shortleaf pine ( Pinus echinata ), longleaf pine ( P. palustrus ) and loblolly pine ( P. taeda ) are found in eastern part of the state. The southwestern white pine ( P. strobiformis ), rocky mountain ponderosa pine ( P. ponderosa var. scopulorum ), pinyon ( P. edulis ) and Mexican pinyon ( P. cembroides ) are found in the western area of the state (west of the Pecos River). All pine trees grown in Texas are susceptible to sawfly attack. The blackheaded pine sawfly ( Neodiprion excitans Rohwer) usually attack larger trees but at least one species, the redheaded pine sawfly ( Neodiprion lecontei Fitch) will defoliate seedlings or sapling trees.
Pine sawfly eggs are laid in clusters and newly hatched larvae frequently feed close together. Often there may be 50-100 larvae feeding in a group. Young larvae eat the outer tissue of the needles while older larvae eat the entire needle and may cause severe defoliation. The insects are most active during late summer and fall. No tree mortality resulting directly from needle loss has been reported but severe defoliation causes loss of tree vigor and increases susceptibility to attack by bark beetles. Larval feeding may can cause unsightly damage to ornamental or landscape plantings as well as trees in nurseries.
The adult female is about 3/8-inch long, brown in color and has a heavy body and thread-like antennae with 13 or more segments. Adult males are slightly smaller in size and have feathery antennae. Full grown larvae are about 1-inch long and depending on the species may be bright yellow with black spots (redheaded pine sawfly) or olive green to nearly black with dark stripes along the sides (blackheaded pine sawfly). Some species are solid green with darker spots. . There is usually o ne generation per year, but there may be a partial second brood.
Sawfly populations are usually kept under damaging levels by natural mortality factors including predators, parasites and pathogens, starvation and unfavorable weather. Population outbreaks can occur when conditions are favorable and natural mortality is low. Damage may be avoided by regular inspection of pine trees to detect and destroy larval populations before individuals reach the late stages when they are most voracious and damaging. Since initial populations are clustered, removing eggs/larvae by hand, and shaking or pruning infested shoots may be an effective control tactic for small trees in landscapes or Christmas tree farms. Repeated applications of nsecticidal soaps and oils may be used as contact sprays to kill eggs and small larvae. Acephate (Orthene ® ), chlorpyrifos (Dursban ® and Lorsban ® ), cyfluthrin (Tempo ® ), deltamethrin (DeltaGard ® ), imidacloprid (Marathon ® , Merit ® and Provado ® ), lambda-cyhalothrin (Demand ® , Scimitar ® and Warrior ® ), permethrin (Astro ® , Dragnet ® and Permethrin Pro ® ), phosmet (Imidan ® ) or spinosad (Conserve ® and Entrust ® ) are labeled insecticides against pine sawfly. Always read and follow directions on pesticide labels.