First evidence of pupal summer diapause in Pieris brassicae L.: the evolution of local adaptedness

Pieris brassicae L. is adapted to a wide variety of local climates throughout the Palaeartic by means of geographic variation in daylengths and temperatures triggering winter diapause. We report for the first time a population from Sotogrande in southern Spain (strain S) that additionally exhibits a pronounced summer diapause in the pupal stage as a response to long daylengths. As well as having diapause triggered by long daylengths, this population develops directly at short, ecologically relevant daylengths. This unusual short-day type response is expressed at temperatures of 21 degrees C and above. The absence of cryptic summer diapause in a population from southern France indicates that this summer diapause evolved locally in Spain or Northern Africa in a population of P. brassicae which lacked this trait. The PPRs of strains S, H (Denmark) and B (France) and crosses between them suggest that summer diapause is inherited as a recessive allele which has a clinal decrease of frequency in populations northwards. The population from southern France shows that this simple pattern of inheritance is further modified by an unknown genetic mechanism controlling the expression of summer diapause near the border between aestivating and non-aestivating populations. On the basis of the photoperiodic response and climatic data we predict P. brassicae to have five or more generations each year in southern Spain.