After years of moderate infestations of gypsy moth, numbers are finally getting very high in northeastern Illinois. Numerous large tree defoliations have been reported in Lake, McHenry, and DuPage counties. In these instances, every leaf has been eaten from the trees, and the caterpillars have then crawled to nearby trees to feed.
Gypsy moth mature larva on maple.
A feature of gypsy moth caterpillar host selection is that newly hatched larvae can feed on fewer host species than older larvae. For instance, newly hatched larvae are more common on oaks, willows, and birches, whereas older larvae can feed on maples; thus the larvae are likely to cause feeding damage on tree species that were not previously attacked.
Gypsy moth caterpillars typically descend from their host trees in late June to pupate and cease to be susceptible to insecticide applications. However, caterpillars still feeding on leaves can be controlled with carbaryl (Sevin), spinosad (Conserve), and pyrethroid insecticides. Realize that these caterpillars will soon quit feeding, and the amount of additional damage that they will cause is minimal. (Phil Nixon and Jim Cavanaugh)