Critical Period for the Influence of Temperature on Egg Size Induction in the Skipper Butterfly, Parnara guttata guttata（Lepidoptera: Hesperiidae）

Abstract

The skipper butterfly Parnara guttata guttata（Bremer et Grey）utilizes temperature as an important cue for producing the optimal reproductive allocation between size and number of eggs in each generation. Reciprocal transfers were made by switching the thermal conditions between a low temperature condition（20°C）, which induces smaller sized eggs, and a high temperature condition（25°C）, which induces larger sized eggs, to investigate the critical period for the regulation of egg size by P. g. guttata in response to temperature. Females laid larger eggs when a high temperature was present during all larval stages or when a low temperature was present only during the fifth（final）instar larval stage. In contrast, smaller eggs occurred in response to any other thermal condition. There was a high correlation between egg size and temperature during the total developmental period of the first and fourth instar larval stages. These results suggest that this species has a mechanism for monitoring thermal conditions twice, i.e., at the first and fourth instar larval stages. The adaptive significance of the response of egg size of P. g. guttata to thermal conditions experienced at the early and middle immature stages was discussed.