Defoliating insects are common in all forest ecosystems, feeding on coniferous and deciduous hosts. They are an integral part of forest ecosystems and may be beneficial or detrimental to the health and productivity of forests. Depending upon the duration and the severity of defoliation, tree growth may be negatively affected; top-kill and eventual tree mortality could result. Feeding is often most severe on suppressed trees, thus defoliating insects may serve as natural thinning agents. Tree mortality due to defoliator feeding can contribute to forest succession. Harvesting, regeneration, and stand management activities can affect the interactive competition, population fluctuations, and spread of defoliator populations. Another aspect of defoliation is nutrient cycling in the form of dead insects, insect frass, and foliage dropped to the ground from wasteful feeding. Damage due to defoliation may have significant effects upon the continuous availability of timber, aesthetics in parks and recreational areas, property values where standing live trees are integral components of the property, watershed and wildlife values, and human health. Early detection and identification of an outbreak and identification of the causal insect are critical initial steps in managing forest defoliators.
Projected damage may be severe enough to warrant treatments, either directly through application of suitable insecticides, or indirectly through harvesting or silviculture treatments. It is very important to consider potential defoliator outbreaks throughout all phases of forest management. Defoliators should be considered at all levels of planning and when creating prescriptions, even though they may not necessarily be treated in all situations.
This guidebook is designed to provide a background to defoliator management and specific practices for managing:
While many other defoliators cause substantial damage in many areas of the province, few proven management tools exist. Therefore, this guidebook does not provide information on these other defoliator species.
Where possible, biological features and activities that are common to the five defoliator species are included in the opening sections of this guide. Those features and practices which differ are described under specific defoliator species. Management practices are discussed in a "how to" manner; extensive background information or the rationales for certain items have not been included in this guide. Key references for specific defoliator species have been listed in the last section of the guidebook.