Developmental and phenotypic responses to photoperiod in uni-and bivoltine Pieris napi in California

• 1 Coastal Californian Pieris napi are facultatively bivoltine, with two seasonal phenotypes, whereas inland populations from the Inner Coast Ranges and Sierra Nevada are univoltine and monophenic.
• 2 When reared under continuous light at 25d?C both coastal and inland stocks produce about 50% diapause pupae, which give rise to vernal-phenotype adults. Non-diapause pupae of all stocks give rise to summer-phenotype adults, even though this phenotype does not exist in the wild in univoltine populations.
• 3 Univoltinism, which implies developmental suppression of the summer phenotype, is interpreted as a derivative from multivoltinism and an adaptation to host plant phenology.