Studies on the fall cankerworm, Alsophila pometaria (Harris) (Lepidoptera: Geometridae) in Manitoba, with reference to performance on different host trees, defoliation intensity and host plant selection
Timlick, Blaine Herbert Leslie.
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Studies were conducted to examine the performance of the fall cankerworm, Alsophila pometaria (Harris), when reared under various conditions, and also to examine adult host selection cues upon eclosion. Fall cankerworm larvae were reared on two age classes of foliage from four species of trees. Cankerworm larvae were also reared on foliage from trees of one species that were under three different degrees of defoliation. Indices of performance were survival, duration of the larval feeding life, prepupal weight, pupal duration, and fecundity of the females. Studies were conducted in both laboratory and field settings. Results indicate that fall cankerworm larvae reared on young foliage have greater performance than do larvae reared on more mature foliage; in general the disadvantage of feeding on mature foliage was less on birch (Betula x sargentii Dugle) and willow (Salix lutea [Nutt.]) than on oak (Quercus macrocarpa Michx.) and elm (Ulmus americana L.). Results suggest that fall cankerworm responds to the changes in foliar quality of Betula x sargentii (Dugle), but it is not clear whether all of these changes are induced by the level of defoliation intensity, or whether other stresses, such as drought, are involved. Results also indicate that both male and female fall cankerworm adults are attracted to vertical silhouettes. The factors influencing the differences and their evolutionary implications are discussed.