EFFECTS OF LARVAL HOST-PLANT AND SEX ON THE PROPENSITY TO ENTER DIAPAUSE IN THE COMMA BUTTERFLY

For polyphagous insects, the choice of host plants by ovipositing fema les may potentially have profound effects on the life histories and li fe cycles of their offspring. This is especially true for insects such as butterflies, that obtain most of the resources needed for adult ma intenance and reproduction during the period of larval feeding. In thi s study we investigate the effect of larval host plant on the propensi ty to enter adult hibernation diapause (and pass through a univoltine life cycle) in the polyphagous comma butterfly, Polygonia c-album (Lep idoptera: Nymphalidae). Host plants resulting in;slow larval growth ra tes (e.g. Betula pubescens) produced a larger proportion of individual s of the hibernating dark morph compared to larval host plants promoti ng a more rapid larval growth (e.g. Urtica dioica). Only the latter ca tegory of plants would support a bivoltine pathway in the field. The e ffect of host plant remained after controlling for growth rate, sugges ting that the host plant may function as a ''cue'' for choice of life cycle, in combination with photoperiod and temperature. Males grew fas ter than females but had a higher propensity to enter diapause. There was also a steeper increase in frequency of diapause for males than fo r females at low temperatures and on poor host plants. This suggests t hat males which cannot achieve protandry under direct development, in situations when high growth rates are too costly, instead enter diapau se.