Abstract
Seasonal changes in adult densities and female mating frequencies of the rice leafroller, Cnaphalocrocis medinalis were observed from 1988 to 1992 in the rice fields of Southern Kyushu, Japan. The ratios of mated females in field populations were high at 75–100% in late June and early July, when adult immigrants invade fields probably from China. In late July and early August, the ratios suddenly dropped to below 50% simultaneously with a rapid rise in adult population density of the first generation. Thereafter, the ratios fluctuated from 25–75%. These seasonal changes were different from the previous report obtained in Northern Kyushu. Based on these results, possible migration of adults within the local habitats and further northward is discussed.
