Pine sawflies

Published June 05, 2017

Left: The larval stage of the redheaded pine sawfly is the stage that does the most damage, feeding on foliage of conifers. Right: In cases of heavy infestation, entire trees can be defoliated.

There are more than 100 species of sawflies known in the U.S., and the most common feed on conifer foliage. Coincidentally, the sawfly is not technically a fly. It is in the order

Hymenoptera, which includes ants, wasps, and bees. The common name “sawfly” comes from the saw-like apparatus at the tip of the adult sawfly’s abdomen. It uses this “saw” to slit plant tissue which allows for easy insertion of eggs. Sawfly larvae 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.

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Appearance

Adult white pine sawfly

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.

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 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 white pine sawfly (N. pinetum) larva is cream color with four rows of black spots on the body and a black head.

Sawfly larvae often feed on older needles, but some species prefer new growth.

Hosts

European pine sawfly can cause heavy defoliation on red, Scots, mugo, Japanese red, and jack pines.

The preferred hosts of redheaded sawfly are two-and-three needle pines (jack, red, Scots, pitch) and some five-needle pines. Introduced pine larvae feed primarily on white pine and other five-needle pines, and white pine sawfly primarily feeds on white pine, but can be found on red, pitch, and mugo pines.

Management

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.

Symptoms

The adult sawfly is less than one-half inch long, resembling a small bee or wasp. The adult sawfly 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, 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.

Source: The Morton Arboretum Photos: Gerald J. Lenhard, Louisiana State University, Bugwood.org; Steven Katovich, USDA Forest Service, Bugwood.org; USDA Forest Service - Region 8 - Southern , USDA Forest Service, Bugwood.org

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