Temperature modulation of photoperiodism: an adaptation for long-distance dispersal in the aphid, Acyrthosiphon pisum (Hemiptera: Aphididae)

Abstract

AbstractVariation in the seasonal occurrence of asexual and sexual phenotypes of Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) is quantified for a local population in southern Manitoba, Canada. To survive winter, summer asexual generations must produce a sexual generation in a timely way at the end of the season, so that females can lay overwintering eggs. This transition is controlled by day length, which varies in a fixed seasonal pattern with latitude, and the local pattern of day length selects for an appropriate photoperiodic response. Substantial variation in the timing of production of males and mating females occurs among locally collected genotypes. Some of the variation is due to the arrival of long-distance dispersers (1000 km or more), and some is consistent with shorter but still long-distance dispersal. Some of the variation is due to year-to-year changes in late summer temperature. The critical day length in nature, which corresponds to critical photoperiod, increases as the average temperature decreases. This temperature modulation is adaptive because it allows many genotypes to produce some sexual phenotypes before the end of the season, although their photoperiodic responses are characteristic of long-distance dispersers and inappropriate to local day lengths.