Red Pine Sawflies

Identification

• Adult sawflies -- miniature, thick-waisted wasps -- visit red pines only to mate, carve needle pockets with saw-toothed abdominal appendages and deposit eggs. White at birth, their tiny larvae develop distinctive coloration as they grow. Mature red-headed pine sawfly larvae have black-spotted, pale-yellow bodies. Black-headed, gray-green red pine sawfly offspring boast light-green undersides, green striped sides and black striped legs. Green-striped, black-headed European sawfly offspring devour older needles before the new ones start emerging. When disturbed, they adopt a U-shape posture. Occasional red pine pests, conifer sawfly larvae have clearly defined, dark-green upper bodies and light-green abdomens.

Damage

• Sawfly larvae feed in groups, some of them containing 100 or more pests. Between hatching and their first molt, they consume the needles' surfaces, leaving straw-colored, wilted cores in their wake. After their first molt and until they drop to the soil to pupate, they devour entire needles. Because conifer, red pine and red-headed sawflies eat old and new foliage, large infestations defoliate the trees. European pine sawflies hatch early in the year, before the new needles emerge. Before pupating, they strip the twigs of old needles, leaving them bare beyond their growing tips. While red pines seldom succumb to sawfly damage, repeated attacks may stunt their growth and weaken their resistance to disease or other insect damage.

Risk Factors

• Sawflies typically target young red pines between 1 and 14 feet high, according to the University of Rhode Island Landscape Horticulture Program. Environmentally stressed trees in excessively wet, dry or shallow soils are susceptible to infestation, as are crowded trees fighting with other plants for moisture and soil nutrients. Because sawflies attack red pines in cycles, however, the trees may outgrow the risk before facing a serious outbreak. When the sawfly populations peak, however, deformity or death are possibilities.

Minimizing Damage

• Minimizing sawfly damage begins with monitoring young trees in the spring for straw-yellow stripped needles. They indicate the presence of new sawfly larvae. After the pests molt into visible colonies, shake them from the trees into a pail of soapy water or prune infested twigs and dispose of them in sealed plastic bags. Peak infestation years may require saturating affected tree parts with insecticidal soap to control recently hatched larvae. Spray on a cloudy day with a solution of 5 tablespoons of liquid dish soap per 1 gallon of soft water and rinse the trees after a few hours to limit potential sun damage.