Abstract

The common eggfly, Hypolimnas bolina (L.) (Lepidoptera:Nymphalidae), is an adult-diapausing tropical and sub-tropical species that exhibits seasonal plasticity in adult body size. Here I investigated (a) whether size plasticity in this species is due solely to variations in rearing temperature, or whether photoperiod is also involved, and (b) whether rearing photoperiod affects the timing of ovarian development in adults. Individuals were cultured at temperatures ranging from 21˚C to 30˚C, and under daylengths of 11.5, 12.5 and 13.5 h in two separate experiments. Significant plasticity in juvenile developmental traits was detected in response to both variables, with cooler temperatures and shorter daylengths both leading to decreased developmental rates and increased size at maturity. Although juveniles grew more slowly with decreasing temperature, they grew faster with decreasing daylength. The timing of ovarian maturation was also related to rearing photoperiod; whereas ‘long day’ adults (13.5-h photoperiod) had gravid ovaries after 10 days, the ovaries of ‘short day’ adults (11.5-h photoperiod) were either regressed or nearly so. These preliminary results suggest that size variation observed in field populations of H. bolina may not be wholly accounted for by variations in developmental temperature and, furthermore, that photoperiod may be used by this tropical species as an environmental cue for the seasonal timing of reproduction.