Diapause as a pivotal factor for latitudinal and seasonal adaptation in Locusta migratoria in Japan

Abstract

The seasonal life cycles and diapause response in Locusta migratoria in Japan are reviewed. This species commonly occurs throughout the Japanese archipelago and diapause plays an important role in controlling the life cycle that varies depending upon the latitude. Photoperiod is an important cue controlling the maternal induction of embryonic diapause in central Japan but not in the northern part where the species is univoltine. In central Japan, heterogeneity in temperature of micro-environments causes large variation in the date of hatching among the overwintered eggs, and individuals hatching late produce only diapause eggs under the influence of short photoperiods, resulting in a mixture of univoltine and bivoltine life cycles. Although the temperate populations can survive winter only as eggs, embryonic diapause is not a pre-requisite for overwintering, and cold hardiness appears to develop even in young eggs before the diapause stage. In the southern, subtropical populations which can overwinter at any developmental stage, large genetic variation appears to exist in the capacity for embryonic diapause, and the induction and termination of diapause are likely to occur in an opportunistic fashion under mild winter conditions. These results indicate that the extensive distribution of this locust has been made possible by its considerable genetic and physiological flexibility.