| General recommendations. Sawflies are not true flies, but rather are in the same order as ants, wasps, and bees. Their name derives from the adult female's abdominal appendage, which she uses to insert eggs in foliage. Adult sawflies have 2 pairs of wings and are dark, wasplike, somewhat flattened insects, usually 1/2" long or shorter. Most surface feeding larvae have six or more prolegs on the abdomen and one large "eye" on each side of the head. An exception is the pear sawfly, whose larva resembles a small, dark olive green slug.
Different sawfly species prefer a variety of hosts. Conifer sawflies chew needles or buds; a few mine in shoots and cause tip dieback. The larvae often feed several to a needle. They can be found throughout the United States. While over 2 dozen species are native, several foreign species have been introduced in the east, for example, the European pine sawfly and the European spruce sawfly. Overall, pine is the most common host of these species, but they can also affect arborvitae, cypress, fir, hemlock, juniper, larch and spruce.
Broadleaf sawfly species cause more variable damage. Some skeletonize or chew holes in leaves; others mine tissue. A few examples are the pear sawfly and the bristly rose slug. The adult pear sawfly is shiny black with dark wings; the larva is described above. Also called the pear slug, this slimy little thing skeletonizes the leaf surface of most fruit trees, especially cherry and pear, less often other trees such as ash or hawthorn. The bristly rose slug is, as the name implies, another sluglike sawfly larva, actually one of several that feed on roses. It is shiny black to pale green; by maturity it develops the many bristlelike hairs on its body whence its name derives. Young larvae skeletonize the lower leaf surfaces of their favored host, while mature larvae chew large holes in leaves.
Fortunately, healthy trees and shrubs tolerate moderate defoliation without significant loss in growth, flowering or fruit yield. Furthermore, a number of natural enemies keep most sawfly populations low, including parasitic wasps, insectivorous birds, small mammals, predaceous beetles, as well as fungal and viral diseases. In eastern states, where introduced species are a menace to Christmas tree farms and forests, sawfly populations have been managed by introducing and/or augmenting sawfly parasites and insect specific viruses. Sawflies in western forests, which are primarily native species, rarely damage forest trees. |
