NC State Extension Publications

Description and Biology

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The introduced pine sawfly, Diprion similis, was first found in the United States in 1914. Stocky yellow and black females lay their eggs end to end by slitting open pine needles and laying the eggs inside. Male introduced sawflies have feathery antennae and are blackish and smaller than females. Each female seals the wounded needle with a frothy secretion that protects the eggs. Tiny caterpillars hatch and begin to feed gregariously on the needles. At first the outer, more tender parts of the needles are consumed so that they curl as they dry out. As the caterpillars grow, they consume the total needle. When fully grown, the caterpillar is about one inch long, and whitish with yellow and black spots and a shiny black head. The mature caterpillar crawl about and spins a tough cocoon inside of which it molts into a pupa. Cocoons are attached to needles, twigs, and bark of host trees and even on other trees nearby. Later, a new generation of sawflies emerges and repeats the life cycle. We have at least two generations each year and sometimes three. This sawfly has been reported primarily in the mountains of North Carolina.

introduced pine sawfly

The introduced pine sawfly is about half inch long.

Introduced pine sawfly caterpillar

Introduced pine sawfly caterpillars grow to about an inch long.

Introduced pine sawfly cocoon

Introduced pine sawfly cocoons are about half inch long.

Introduced pine sawfly eggs

Introduced pine sawfly eggs are completely hidden within a needle.

Host Plants

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The introduced pine sawfly has been reported to attack and develop upon a number of species of Pinus, especially eastern white pine, but it also infests Scot's pine, jack pine, and red pine. First generation caterpillars feed on the previous year's needles. Second generation caterpillars feed on new and old needles. Older larvae feed singly and eat entire needles and even bark after the needles are gone. Defoliation is usually most severe in the upper half of trees.

Introduced pine sawflies

Introduced pine sawflies usually attack upper branches of white pine.

Residential Recommendations

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A parasitic wasp, Exenterus amictorius, attacks mature caterpillars. Another wasp, Monodontomerus dentipes, attacks cocoons and destroys their contents. Monodontomerus is credited with keeping the introduced pine sawfly pretty much under control in North Carolina. The introduced pine sawfly is not reported to be resistant to pesticides, so most insecticides labeled for landscape use found in garden centers should give more than adequate control.


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This Factsheet has not been peer reviewed.


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Publication date: Aug. 7, 2015
Revised: Sept. 24, 2019

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