Defoliating insects are common on most of the commercially valuable tree species in the province. Many are host specific. Table 1 lists five major forest insect defoliators and their hosts. All of the major defoliators discussed in this manual belong to the order Lepidoptera. The larval stages of these defoliators cause damage to the trees through active feeding on the foliage.
It is critical to understand the life history of defoliators in order to plan and implement management strategies and treatments (Table 2). Timing and type of treatment will change depending on the defoliator present in the stand. Defoliators cause similar visible damage, therefore it is critical to correctly identify the causal agent. Table 3 describes the various life stages of five major defoliator species in B.C.
Although defoliators may be found throughout their primary host's range, outbreaks tend to occur in localized or historic areas. Figures 1, 4 and 5 show the distribution and defoliation history in the province of Douglas-fir tussock moth, eastern spruce budworm, and western blackheaded budworm respectively. Figure 2 shows the relative risk of defoliation by the western spruce budworm throughout B.C. The risk has been determined by analysing the frequency and periodicity of defoliation in areas where outbreaks have occurred. Figure 3 is a frequency analysis of defoliation by the western hemlock looper.