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Scarlet Oak Sawfly

Oak sawfly larvae-feeding activity Branch defoliated by the oak sawfly

Oak sawfly larvae-feeding activity
USDA Forest  Service

Branch defoliated by the oak sawfly
USDA Forest Service

The scarlet oak sawfly, Caliroa quercuscoccineae (Dyar) skeletonizes leaves of scarlet, black, pin, and white oaks in eastern North America. It is also called the oak slug sawfly because of the fact that the larvae are covered with a coat of slime that helps them adhere to foliage.  

Larvae feed on the lower surface of the leaves, leaving only a fine network of veins which gives the leaf a transparent appearance. Defoliation starts in the upper crown in early summer and progresses downward. By late summer, heavily infested trees may be completely skeletonized. 

Larvae overwinter in cocoons in the litter layer, and adults emerge in the spring. The adults, which resemble small fly-like insects, are about 6-8 mm long and are black with light yellowish legs. Females lay eggs in rows in the lower leaf surface along the sides of the midribs and larger veins. Eggs hatch within 1-2 weeks, depending on the temperature. Several larvae feed on the same leaf. Full-grown larvae are slug-like, yellowish-green, and about 12 mm long. There may be two to three generations per year. 

Microbial diseases and other natural enemies generally keep the sawfly in check. In outbreak years, insecticides may be needed on high-value trees. 

Information provided by the USDA Forest Service