. Insect and disease conditions in the United States, 1979-83 : what else is growing in our forests?. Forest insects United States; Trees Diseases and pests United States; Plants Disease and pest resistance. Western Spruce Budworm In 5 Years, Defoliation More Than Doubled Written by David R. Bridgwater Anative defoliator, the western spruce budworm lives in the mixed conifer forests from southern New Mexico to Canada. Each year, this insect defoliates millions of acres. In 1983, for instance, defoliation caused by the western spruce budworm was visible on about 11 million acres ( million ha
. Insect and disease conditions in the United States, 1979-83 : what else is growing in our forests?. Forest insects United States; Trees Diseases and pests United States; Plants Disease and pest resistance. Western Spruce Budworm In 5 Years, Defoliation More Than Doubled Written by David R. Bridgwater Anative defoliator, the western spruce budworm lives in the mixed conifer forests from southern New Mexico to Canada. Each year, this insect defoliates millions of acres. In 1983, for instance, defoliation caused by the western spruce budworm was visible on about 11 million acres ( million ha). Yet over most of its range, the western spruce budworm does its damage unobtrusively. The bud- worm larvae (fig. 1) feed on the expanding buds and new needles of host trees. Although this feeding saps the tree, the damage is hardly visible during the first or even the second year of suc- cessive defoliation. But when the budworm repeatedly defoliates a tree, the tree begins to die from the top downward (fig. 2). Defolia- tion also causes the tree to grow more slowly. The budworm usually develops from egg to adult in 1 year. In August, moths emerge from pupal cases, and females lay eggs on the needles of host trees. When the eggs hatch, the tiny larvae spin silken webs in sheltered locations on the tree, where they spend the winter. The following May, the larvae come out from their hiding places, bore into developing buds, and begin feeding. As the new shoots unfurl, the larvae spin loose webs between the needles and continue to feed. When fully grown, the larvae pupate. Adult moths emerge from pupal cases in August. The life cycle begins again. The larvae feed on a variety of trees. The most common hosts are Douglas-fir; true firs, such as grand fir; and spruce. The larvae also feed on coniferous trees that. Figure 1. Full- grown larva of western spruce budworm. F-702981. Please note that these images are extracted from scanned page images that may have been digitally enhanc
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