抄録
Oxya yezoensis has been resurging in paddy fields during the last several years in Japan. Surveys mad in 1989-1992 showed that this grasshopper occurred in at least 45 out of 71 localities between 31°N and 43°N. O. yezoensis was abundant in northeastern Honshu, and was found, at restricted sites only, in Hokkaido, southwestern Honshu, and Kyushu. Many local samples collected in late autumn contained nymphs, and systematic samplings in Hirosaki (40°33'N) showed continuous occurrence of 1st-instar nymphs from late May to October. The critical data of hatching for emergence as an adult was August 25 in 1990 and August 20 in 1991. Eggs of the Hirosaki strain entered an obligatory diapause at 20-35°C. Those from other localities also entered diapause. Therefore, it is likely that the occurrence of 1st-instar nymphs in autumn does not represent a partial second generation but derives from delayed hatching of overwintering eggs.
