The Biology of the Pine Webworm, Tetralopha robustella, in Wisconsin1

Abstract

The pine webworm, Tetralopha robusrtella Zeller, is a potential pest in Wisconsin as a defoliator of red and jack pines. Its life history and habits were studied in a plantation of red pine and a natural stand of jack pine on the sandy Wisconsin River valley. The webworm is widely distributed throughout the eastern half of the United States, and has been recorded on 10 species of pine. An analysis of head capsule measurements using Dyar's Rule indicates six instars. A general description of eggs, larvae, cocoons, and adults of the webworm is given. Webworm larvae overwinter in sand-covered cocoons within the first inch of soil beneath the host tree. Pupation occurs in early June and adults emerge about two weeks later. Oviposition begins in early July and continues until mid-August. Larvae appear in early July and spend at least the first instar mining needles. Then they leave the needles and construct frass shelters in which several live for the remainder of the larval feeding period. They begin to abandon the nest to enter the ground to overwinter in mid-September; some remain in the frass nest until mid-November. Eight parasites and two insect predators were found feeding on the webworm. Twig and branch foraging birds were also observed destroying frass nests and eating webworms.