Abstract
Variation in the summer-diapause expression of the ladybird beetle, Coccinella septempunctata, among local populations and years was investigated by field observation and dissection of sampled specimens, in Japan. Only non-diapausing adults were found in Hokkaido, northern Japan, whereas diapausing adults were observed at most sites in Honshu and southward in summer. However, the non-diapausing adults were also observed in northern Honshu and at high-altitudinal sites of central Honshu. The frequency of diapause expression in northern Honshu varied greatly among populations and years. The frequency of non-diapausing adults was significantly higher when average daily mean air temperature for July was relatively low. This indicated that the populations inhabiting northern Honshu have plasticity in diapause induction, primarily in response to temperature conditions. Moreover, the coexistence of diapausing adults and non-diapausing adults at the same site was often observed. This suggested that there might be genetic variation in diapause tendency within a local population.
