Seasonal Changes of the Proportions of Mated Females in the Field Population of the Rice Leaf Roller, Cnaphalocrocis medinalis GUENEE (Lepidoptera : Pyralidae)

Abstract

Observations were made of the mating, ovarian development and fat condition of the rice leaf roller, Cnaphalocrocis medinalis Guenee, collected from fields and by light trap in 1977 and 1978. It became clear that the proportions of the mated females fluctuated extremely by season. Most of the females collected in the paddy fields mated from June to early September. Thereafter, the proportions of mated females declined greatly up to mid-October, when almost all female moths contained immature ovaries and abundant fat body in their abdoments. From late October through the rest of the season the mated females, most of which looked lean, increased considerably in number. Some difference of the reproductive conditions was also noted among the three kinds of samples : female moths collected in the paddy fields, in the grassy fields and those captured by light trap. Some possible causes for the disappearance of the mated females in autumn are discussed.