Abstract
Reproduction and wing patterns (shape and colouration) in Polygonia c-aureum L. (Lepidoptera: Nymphalidae) are regulated by both photoperiod and temperature experienced during the immature stages, which result in the development of summer or autumn forms. The critical day length for this seasonal change in form was 13.5L : 10.5D at 21°C and 13L : 11D at 25°C. We investigated the connection between seasonal form and female reproduction. Under a 15L : 9D photoperiod at 21°C, reproductively active summer form butterflies are produced, whereas under an 8L : 16D photoperiod at 21°C autumn form butterflies with a strong tendency to enter diapause were produced. On the other hand, under the critical day lengths at 21 or 25°C, autumn form butterflies developed with a weak tendency to enter diapause. When the adult butterflies were transferred from a critical or a short photoperiod to a long photoperiod shortly after emergence, the former were more likely to terminate diapause than the latter. If individuals are reared throughout their entire life cycle under a short photoperiod at 21°C, all the adults have a strong tendency to enter diapause. These results reveal the quantitative effects of photoperiod on diapause in this butterfly and strongly indicate that the determination of the autumn form and induction and maintenance of diapause are not rigidly coupled, at least under laboratory conditions.
Highlights
IntroductionVarious patterns exist in the relationship between seasonal forms or change in body colouration and diapause depending on the species
Seasonal polyphenism is recorded in many insects (Tauber et al, 1986)
The present study shows that more eggs matured in the ovaries of adults of the autumn-form of P. c-aureum that were reared under a critical photoperiod (Figs 1 and 2) but transferred to a long photoperiod at the adult stage, but not in the ovaries of those that were reared under short day conditions (Figs 4 and 6)
Summary
Various patterns exist in the relationship between seasonal forms or change in body colouration and diapause depending on the species. As the planthopper Stirellus bicolor Van Duzee does not enter diapause, its polyphenism is not related to diapause (Whitcomb et al, 1972; Tauber et al, 1986). In the rice skipper Parnara guttata guttata (Bremer & Grey) and the horned beetle Allomyrina dichotoma (L.), it is the larvae that enter diapause and larval diapause is not tightly coupled with differences in the imaginal seasonal forms (Ishii & Hidaka, 1979; Nakasuji & Kimura, 1984; Plaistow et al, 2005). There are species in which there is a close relationship and both seasonal form and diapause are expressed in the same imaginal stage, for example, in the lacewings Chrysopa carnea (Stephens) (Tauber & Tauber, 1970), C. congrua (Walker) (Winterton, 1999), and C. sp. There are species in which there is a close relationship and both seasonal form and diapause are expressed in the same imaginal stage, for example, in the lacewings Chrysopa carnea (Stephens) (Tauber & Tauber, 1970), C. congrua (Walker) (Winterton, 1999), and C. sp. (Canard, 2005), as well as the rape bug Eurydema oleracea (L.) (Fasulati, 1979), stink bug Plautia crossota stali Scott (Kotaki & Yagi, 1987; Kotaki, 1998a, b), brown stink bug Euschis-
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