Northward expansion and climatic factors affecting the distribution limits of Cheilomenes sexmaculata (Coleoptera: Coccinellidae) in Japan

The distributional expansion of the ladybird beetle Cheilomenes sexmaculata (Fabricius) in Japan was analyzed based on literature surveys and observations of 1,312 individual specimens collected from 1918 to 2005. An expansion toward higher latitudes, from Kyushu (33A degrees N) to central Honshu (36A degrees N), was observed between 1910 and the early 1990s. Multiple regression analysis showed that the presence of this beetle was associated with an annual mean temperature but not with the mean minimum temperature in the coldest month, and 95 % occurrence probability of this beetle was obtained in a locality at 15.1 A degrees C annual mean temperature. The northward expansion of this species synchronizes with increasing areas where an annual mean temperature is more than 15 A degrees C. Therefore, climatic warming over the past 100 years is considered as a major factor influencing the northward expansion of this species.