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White Pine Sawfly

September 12, 2001

White pine sawfly, Neodiprion pinetum, has been noticed feeding on white pine, Pinus strobus, in northwestern Illinois. Although it feeds mainly on white pine, it also attacks red, Mugo, and other short-needled pines. White pine sawfly feeds from July through September and if left unchecked can cause severe damage to pines.

Adult sawflies are broad-bodied, with a thick abdomen, and have membranous wings. Females are larger and more robust than males. Sawfly females have a sawlike ovipositor, which they use to create slits or cuts in plant tissue. Eggs are then inserted into these slits, generally located on the edge of needles. A A female can lay up to 100 eggs during her lifetime. The females don’t need to mate to produce eggs; however, unfertilized eggs produce only males, whereas fertilized eggs produce both males and females.

Eggs hatch into larvae that are 1/4 to 1/2 inch long. The larvae are yellow- to cream-colored and have a deep black head. Four longitudinal rows of black spots run the length of the body, and a posterior black spot is at the end of the abdomen. Larvae feed gregariously on both the old and new foliage of pines. First-instar sawfly larvae generally consume only the outer part of a needle; later instars eat the entire needle. The heaviest feeding activity occurs in summer through early fall (July through September). Sawfly larvae initially resemble the caterpillars of moths and butterflies. However, sawfly larvae have more than five pairs of prolegs on the abdomen, which lacks the hooked spines (crochets) typical of caterpillars. Caterpillars have between two to five pairs of prolegs.

White pine sawfly spends the winter as a prepupa, a stage between larva and pupa, in a cocoon that is generally located on the ground underneath host trees. Pupation is completed in spring, and adults emerge several weeks later. One generation is typical in Illinois, as most of the white pine sawfly problems occur in the northwest portion of the state.

White pine sawfly can be managed with pest-control materials such as acephate (Orthene), azadirachtin (Azatin/Ornazin), carbaryl (Sevin), chlorpyrifos (Dursban), and spinosad (Conserve). Spray applications should be made when larvae are small and feeding on needles. The microbial insecticide, Bacillus thuringiensis var. kurstaki (Dipel, Thuricide, and Javelin), that is used for controlling caterpillars, does not work on sawflies because sawflies are closely related to wasps and ants. Btk is effective against only the larvae of moths and butterflies.

Author: Raymond A. Cloyd


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