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Joseph F. Boggs, Ohio State University Extension, Hamilton County/Southwest District; Curtis E. Young, David J. Shetlar, James A. Chatfield, Erik A. Draper, Pamela J. Bennett, Gary Y. Gao, |
Sawfly Defoliators
Overwintered eggs of the European pine sawfly (Neodiprion sertifer) hatched in mid-April in central and southern Ohio. Last season, eggs hatched in southern Ohio in mid-March (8). In 1998 and 1999, eggs hatched in that part of the state in early April (6, 7). Conifer hosts include mugo, table top, Scotch, red, Jack, and Japanese pines. Larvae feed in colonies, but this sawfly has only one generation per year, and larval development is generally completed before new growth occurs. Consequently, damage is usually confined to the previous years' needles. Although this sawfly was commonly found during the spring, no significant outbreaks were reported.
The redheaded pine sawfly (N. lecontei) is a more serious conifer pest and appeared to be on the rise in southern Ohio during past seasons (1, 2, 7, 8). Unlike the European pine sawfly, the redheaded pine sawfly has at least two generations per year, and it spends the winter as late-instar larvae in a cocoon. During the spring, this sawfly completes its development, emerges, and lays eggs in needles. By the time eggs hatch, new growth has usually started to elongate. Larvae feed in colonies on new and old needles, and occasionally on the tender bark of young twigs, particularly during the second generation. Because old and current needles are eaten, this sawfly is considered to be one of the most destructive of the pine sawflies. Destructive populations were observed during the 2001 season on mugo pines in landscapes and on Scotch pines in Christmas tree plantations in southwestern Ohio.
As with last season, pockets of high populations of dusky birch sawfly (Croesus latitarsus) were observed in Cincinnati, Ohio, this season (8). This sawfly also has two generations per year, and it feeds on birch leaves. Early instar larvae skeletonize leaves and later instars consume entire leaves, except for the mid-vein. All instars have shiny black head capsules and distinct black spots on their bodies, but middle-instar larvae are greenish-gray and become yellowish-green when they reach the last instar stage. All instars feed in colonies, lined up head-to-tail along leaf margins. When disturbed, the larvae exhibit a characteristic defense posture they hang on with their prolegs and form their bodies into a distinct "S" shape. Entire colonies practice this defense posture in unison, forming a row of Ss, which is a great self-identifier–S for sawfly!