Ecophysiological studies on invertebrate diapause

Abstract

Diapause performs two main functions in the life-cycle of an insect. In addition to protecting the organism from adverse seasonal conditions it synchronises active stages of development with optimal conditions for growth. In most temperate species studied photoperiod and temperature are the two principal zeitgebers involved in insect periodicity and diapause expression. Generally insects respond to either quantitative changes in day-length or according to a fixed critical threshold of light. The rate of diapause development is controlled primarily by temperature, as numerous studies have demonstrated that chilling hastens termination of dormancy in a large number of autumnal-hibernal diapausing insects. This study focused on the effects of photoperiod and temperature on a number of diapausing insect species found around County Durham. In the cranefly Tipula subnodicornis, larvae subjected to a critical regime equal to or below L:D 12:12 pupated significantly later than individuals kept on a regime of L:D 14:10 and above. In the carabid beetle Nebria salina, long-day suppressed ovarian maturation whereas short-day favoured egg development. Male reproductive development occurred irrespective of the applied photoperiod. In Tipula fusca and Coleophora alticolella, chilling hastened development towards hatching and adult emergence, respectively. Intraspecific variation in response to the combined effects of chilling and photoperiod was observed in C. alticolella and the relevance of such findings in the field were discussed.