Voltinism and the Induction of Aestival Diapause in the Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Abstract

Field studies over 3 yr demonstrated that overwintering populations of the Colorado potato beetle in upstate New York and on Long Island are composed of adults from both the first and second summer generations. The two populations from the climatically different regions differ in their responses to environmental factors that influence voltinism. The critical photoperiod for aestival diapause induction is longer, and the induction of diapause by low temperature is greater, in the population from the cooler, inland locality (upstate New York) than in the population from the warm coastal area (Long Island). Under the long days of early summer, temperature appears to influence aestival diapause induction and voltinism at both localities. A large proportion of first-generation adults enters diapause either without ovipositing or after ovipositing for a brief period. These responses have significance for the evolution of the beetle's life history and for its population dynamics and management. KNOWLEDGE of the primary factors that influence phenological traits is essential for understanding evolutionary adaptations to temporally and spa­ tially varying habitats. It is also essential for pre­ dicting development and activity in the field, and, in the case of economic pests, for developing long­ term, reliable methods for management. Although many significant phenological characteristics of the Colorado potato beetle, Leptinotarsa decemlinea­ ta (Say), are known (see specifics below), vital ques­ tions remain regarding the timing and number of summer generations, the occurrence of aestival dia­ pause in North America, and the contribution that the early and late-summer generations make to the overwintering population. A variety of factors can interact to influence voltinism and imaginal diapause in the Colorado potato beetle. Pioneering work by European work­ ers elucidated the behavioral and physiological characteristics of diapause and the important role of photoperiod in diapause induction (Jermy & Saringer 1955; Goryshin 1956, 1958; de Wilde et