Hibernation Site and Dispersal of Spruce Budworm Larvae as Related to Damage of Sapling Balsam Fir

Abstract

The spruce budworm, Choristoneura fumiferana (Clemens), in the Lake States is primarily a pest of mature spruce-fir stands. Yet during the most recent outbreak, heavy infestations occurred on large areas of sapling stands in northeastern Minnesota. Budworms invaded these areas from infested mature stands by dispersal during the adult or early larval stages. Larvae were able to persist initially in the young stands by hibernating on scattered overstory cull spruce trees left from previous logging. From these trees larvae dispersed to the saplings, the dispersal distance depending on several factors including windspeed and length of thread spun by a larva. Laboratory studies showed that the buoyant effect of the silk increased exponentially with length of the thread. Once on the balsam fir, Abies balsamea (L.) Mill., saplings, the larvae produced hollwed-out vegetative buds during early spring feeding. These buds subsequently served s suitable hibernation sites where none existed before. Removal of the residual host tree is recommended as a preventive control technique.