Importance. -- This pest skeletonizes leaves of red and white oaks. Repeated defoliations retard growth, vigor, and mast crops, and kill some trees. It is also called the slug oak sawfly because the larvae are covered with a coat of slime that helps them ahdere to foliage.

Identifying the Insect (figure 8a). -- Larvae are slug-like, yellowish green and shiny with a black head and legs, and .5 inch (12 mm) long. Larvae feed in groups. The adult is a typical sawfly, about .25 inch (6-8 mm) long, and light brown.

Identifying the Injury (figure 8b). -- Leaves may be skeletonized. Larvae consume the lower surface of the leaves, making the leaf transparent. Defoliation starts in the upper crown in early summer and progresses downward. By late summer, heavily infested trees may be completely defoliated.

Biology. -- Larvae in cocoons survive the winter. Larvae pupate in the spring. Adults and larvae are present throughout the summer. Eggs are deposited in single rows of slits on the lower leaf surface along main veins. There are two to three generations per year.

Control. -- Microbial diseases and other natural enemies generally keep the slug oak sawfly in check. Insecticides may be needed on high value trees.

Figure 8. -- (a) Slug oak sawfly larvae; (b) feeding injury by slug oak sawfly.