Intra- and inter-clonal variation in gypsy moth larval performance on bigtooth and trembling aspen

Abstract

A field study on the effects of interclonal and intraclonal variations of aspens on the performance of gypsy moth, Lymantriadispar (L.), was conducted in Michigan during 1988 and 1989. Study species were trembling aspen, Populustremuloides Michx., and bigtooth aspen, Populusgrandidentata Michx. Larvae were caged on intact host trees in the field in fine mesh bags. We examined the leaf phenological development of aspen clones and its relationship to a number of insect parameters: larval weight, relative growth rates, survival, and pupal weights. Interclonal variations in larval growth on trembling aspen clones and bigtooth aspen clones were high in 1988 and 1989. Leaf phenological differences between clones also were highly significant. These differences in leaf phenology led to a window of vulnerability existing for each clone. While insects that initiated feeding on phenologically delayed clones had poorer survival and lower growth rates than did larvae on more phenologically advanced clones, later in the season these larvae were able to catch up as the phenology of delayed clones caught up to that of more advanced clones. Because of this, pupal weights did not show significant effects of clones. Intraclonal variation in larval growth was extremely low for all growth periods. While there were significant differences in phenology between ramets within clones, the variation was much less than the variation seen in phenological differences between clones. Phenology of caged branches within a tree did not vary significantly for either species.