Effects of the Destruction of the Current Year's Foliage of Balsam Fir on the Fecundity and Habits of Flight of the Spruce Budworm

Abstract

When spruce budworm larvae emerge in the spring, they either mine the needles of old foliage or feed upon the freshly opened staminate flowers of balsam fir. As soon as the vegetative buds begin to expand, the larvae abandon the needle mines for this newer and more succulent growth. Later, when the pollen is shed, the staminate flowers are in turn abandoned in favour of new shoots. Usually, the larvae continue to feed on the new shoots until pupation. When this insect reaches epidemic proportions, however, the current year's growth is often totally destroyed prior to the completion of the larval stage. Late spring frosts have also been known to destroy, in part, or even completely, the shoots of the current year's growth. Under these conditions spruce budworm larvae must resort to feeding on old foliage.