HOST-PLANT QUALITY INFLUENCES DIAPAUSE AND VOLTINISM IN A POLYPHAGOUS INSECT HERBIVORE

Abstract

Facultative diapause is a strategy that allows insects to initiate an additional generation when conditions are favorable, or to enter diapause when they are not. The occurrence of additional generations within one year can have a profound effect on the ecology and evolution of a species. Most previous studies of the cues that induce facultative diapause in insects have concentrated on photoperiod and temperature. In contrast, we studied the effects of host-plant quality on the induction of larval diapause and subsequent voltinism in a polyphagous insect herbivore, Choristoneura rosaceana (Lepidoptera: Tortricidae). Field experiments demonstrated that the proportion of larvae entering diapause differed among four host-plant species. Larvae feeding on chokecherry were more likely to continue development and produce a second generation than larvae feeding on red maple or black ash. Paper birch was intermediate in diapause induction. Laboratory experiments with excised foliage supported the results of the field experiments and demonstrated that the induction of diapause depended on host species under constant conditions of photoperiod and temperature. A further study with low- and high-quality artificial diet demonstrated that the nutritional quality of larval diet has a direct effect on diapause induction: low-quality diet favored diapause induction. Dispersal of neonate larvae from host foliage did not necessarily reflect host quality and the potential for bivoltinism. We argue that the effect of plant quality on diapause induction in natural populations of insect herbivores merits more attention.