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The two most common species of pine sawflies which occur in Rhode Island are the redheaded pine sawfly and the European pine sawfly. The redheaded pine sawfly occurs from S.E. Canada throughout the eastern U.S, and is the most widespread and destructive of the pine sawflies. Feeding is primarily restricted to the two- and three-needled pines, such as Jack, red, shortleaf, loblolly, slash, longleaf and pitch pines. White pine and Norway spruce may also be defoliated by the redheaded sawfly. The European pine sawfly, which was accidentally introduced from Europe, is common from southwestern Ontario through New England and west to Iowa. The European pine sawfly is the most common sawfly in ornamental nurseries and Christmas tree plantations. In landscape situations, this sawfly prefers mugho and table top pines. However, it readily attacks Scotch, red, Jack and Japanese pines as well. It will rarely feed on white, Austrian, Ponderosa, shortleaf and pitch pines, especially if these are intermixed with the preferred hosts. Description & Life Cycle: Sawfly adults look similar to true flies, yet have two pair of wings instead of one pair. Sawfly larvae resemble caterpillars, yet have at least six pairs of "stublike" prolegs behind the three pairs of true legs on the insect's abdomen (caterpillars never have more than five pairs of prolegs). Redheaded pine sawfly: Adult females are 6 to 9.5 mm (1/4 to 3/8 inch) in length while males are 5 to 6.5 mm (1/5 to 1/4 inch) long. Males are completely black except for their legs and wings, and females are predominantly black with a whitish underside of the abdomen. Redheaded pine sawfly eggs are oval, 0.5 mm (1/32 inch) long and 0.25 mm (1/64 inch) wide. They are laid individually in a row of slits cut into the edge of the needles. All eggs laid by a female are generally grouped on needles of a single twig. Larvae emerge from eggs 2 to 5 mm (1/16 to 1/5 inch) long. After feeding, the larval body develops black spots and the head capsule becomes orange-red. In the fourth and fifth instars, black spots surround the eyes and the body is deep-yellow. The larvae spin cocoons to overwinter and pupate in. The cocoons are red-brown, cylindrical with rounded ends, and are 10 mm (../images/8 inch) long for females and 7.5 mm (5/16 inch) long for males. There are two to three generations/year. The redheaded pine sawfly overwinters in the prepupal stage in its cocoon spun in the litter of the soil beneath the infested trees. Pupation occurs soon after the onset of spring warm weather, and adults emerge in a few weeks. Eggs deposited in the needles hatch in three to five weeks. Larvae feed gregariously on new and old needles and also on the tender bark of young twigs. Larvae begin spinning cocoons in late June or early July. Second generation adults emerge in July and August. Larvae feed through September and then spin their cocoons. In warmer areas, adults will emerge at the end of September to late October and lay eggs for a third generation that remains active into December.
European pine sawfly: Usually only one generation occurs and the winter is spent as an egg inserted into slits along the edge of needles. The eggs hatch in April through mid-May and the larvae may feed until mid-June. The caterpillar-like larvae are grayish-green and have a light stripe down the back and a light stripe along each side followed by a dark green stripe. Fully grown larvae are about 25 mm (1 inch) long. The larvae feed in groups or colonies, often with three or four feeding together on a single needle. Distributed larvae raise their heads and tails in a threatening manner. Mature larvae drop to the ground and spin tough, brown cocoons in the duff. A few larvae may pupate on the tree. The adults emerge in late August through September to mate and lay eggs. Each female lays six to eight eggs in a single needle and 10 to 12 needles are used. These eggs can be located after a hard frost turns the egg laying scar yellow. Damage: Pine sawflies usually feed on young trees, preferably 0.3 to 4.6 m (1 to 14 feet) tall. Trees growing under stress in shallow soils, very wet or dry sites, or under stress from competing vegetation are especially susceptible to infestation and heavy defoliation. Outbreaks occur periodically and tend to subside after a few years of heavy defoliation. Severe outbreaks have resulted in death or deformity of young pines. The first instar larvae (the ones hatching from the egg) can only eat the needle surface, causing the needles to turn brown and wilt, giving a straw-like appearance to the needles. As the larvae grow, they remain together and feed from the tip of a needle to the base. The larvae feed on older foliage and move from branch to branch as they strip the needles. Trees which are entirely defoliated are severely stunted, but since the new growth is rarely attacked, the trees will survive. Larvae will often migrate to new trees if the needles on their current host have been devoured. Heavily infested trees end up with a "bottle brush" effect--all the old needles are missing and only the current year's needles are present. Control: Numerous natural control agents play important roles in keeping redheaded pine sawfly populations down. Outbreaks often collapse from rodents feeding on the pupae and diseases killing the larvae. Of the 58 species of parasitic and predatory insects affecting this pest, the native egg parasite Closterocerus cinctipennis Ashmead (Hymenoptera) and the larval parasite Spathimeigenia spp. (Diptera) are the most important. Best controls are obtained when the larvae are still small, so look for the straw-like needles left behind by the young larvae. Inspections should be made in late April and early May. The egg laying scars can also be seen by inspecting the needles in late winter. Cultural Control: • Remove competing vegetation before planting pines. • Avoid planting pines in high hazard areas such as frost pockets, or on excessively dry, wet or nutrient-deficient soils. • Promote early closure of pines to prevent competing vegetation such as weeds or hardwoods. Mechanical Control: • Egg Removal - If the needles containing overwintered eggs can be found before they hatch, they can be pulled off the plants and destroyed. Do not simply throw them on the ground, as the eggs can still hatch. •Colonies of larvae can be easily removed by clipping off the infested branch. Place these branches in a plastic bag and destroy. Colonies can also be knocked off by sharply striking the infested branch. Crush the larvae or knock them into a pail of soapy water. If few colonies are present, they can be controlled using these methods, but large infestations are better controlled by general spraying. Insecticides: When deemed necessary, chemical treatments can be used as an effective control. Several horticultural oils (often called "summer" or "verdant" oils) and insecticidal soaps are labeled for control of sawflies on ornamentals. These usually work well when the sawfly larvae are small and thorough coverage of the colony can be achieved.
Adapted from the Virginia Cooperative Extension and the Ohio State University Extension, 1999
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