There are more than 100 species of sawflies known in the United States, and the most common feed on conifer foliage. In reality, the sawfly is not a fly, but in the order Hymenoptera, which includes ants, wasps, and bees. It gets the common name “sawfly” because of the adult stage of its life cycle. The adult sawfly has a saw-like apparatus at the tip of its abdomen, which it uses to slit plant tissue to allow for easy insertion of eggs. The larvae of sawfly resemble that of moth and butterfly caterpillars, but have six or more pairs of false legs (prolegs) on their abdomen. Caterpillars have five or fewer pairs of prolegs.
The adult sawfly is less than one-half inch long, resembling a small bee or wasp. It does very little damage to plants. Most damage occurs during the caterpillar-like stage of development. The larvae feed for weeks on the foliage of conifers, except cedar, hemlock, and juniper. Usually, the larvae feed on older needles, in groups or singly, although some species prefer new growth. Needles can be partially chewed, an entire branch can be defoliated, or, in the case of heavy infestation, an entire tree can be defoliated.
The European pine sawfly (Neodiprion sertifer) is the most common sawfly and a gregarious feeder. It feeds only on old needles. The mature larva has a black head and gray-green body with several light and dark green stripes that break up into spots.
In late spring, after larvae mature and finish feeding, they drop to the ground and spin a cocoon in the leaf litter under the host tree. Pupation occurs in late summer. The adults emerge, mate, and the female deposits more than 100 eggs into the edges of several needles. The European pine sawfly overwinters in the egg stage. The following spring, the eggs hatch and young larvae begin feeding on the outer edges of the needles. There is usually one generation per year. This insect can cause heavy defoliation on red, Scots, mugo, Japanese red, and jack pines.
The redheaded sawfly (Neodiprion lecontei) is a cream colored larva, about an inch long when fully grown. It has a red head with six irregular, black spots along its body. The preferred hosts are two-and-three needle pines (jack, red, Scots, pitch) and some five-needle pines.
The introduced pine sawfly (Diprion similis) larva is about an inch in length, yellowish green with two black stripes down the back with mottled sides, and a black head. The larvae feed primarily on white pine and other five-needle pines, The white pine sawfly (Neodiprion pinetum) larva is cream color with four rows of black spots on the body and a black head. It feeds primarily on white pine, but can be found on red, pitch, and mugo pines.
Nonchemical: Healthy trees and shrubs will tolerate light infestations of sawflies, but inspect trees periodically during the growing season to prevent severe damage. Removing by hand is effective. Wash larvae from plant with a forceful stream of water.
Chemical: Chemical treatments are seldom needed. Spray only when larvae are small and feeding on the needles. During normal spring weather, this is also the time when Saucer Magnolia (Magnolia x soulangiana) is dropping its petals, or Serviceberry (Amelanchier species) is in full bloom.
Contact the Plant Clinic (630-719-2424 or plantclinic@mortonarb.org) for current recommendations. Use pesticides safely and wisely; read and follow label directions.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.