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 females may potentially have profound effects on the life histories and life cycles of their offspring. This is especially true for insects such as butterflies, that obtain most of the resources needed for adult maintenance and reproduction during the period of larval feeding. In this study we investigate the effect of larval host plant on the propensity to enter adult hibernation diapause (and pass through a univoltine life cycle) in the polyphagous comma butterfly, Polygonia c-album (Lepidoptera: Nymphalidae). Host plants resulting in slow larval growth rates (e.g. Betula pubescens) produced a larger proportion of individuals of the hibernating dark morph compared to larval host plants promoting a more rapid larval growth (e.g. Urtica dioica). Only the latter category of plants would support a bivoltine pathway in the field. The effect of host plant remained after controlling for growth rate, suggesting that the host plant may function as a cue for choice of life cycle, in combination with photoperiod and temperature. Males grew faster than females but had a higher propensity to enter diapause. There was also a steeper increase in frequency of diapause for males than for females at low temperatures and on poor host plants. This suggests that males which cannot achieve protandry under direct development, in situations when high growth rates are too costly, instead enter diapause.