1977年筑後におけるコブノメイガの発生消長

Abstract

The population densities of larvae and adults of the rice leaf roller, Cnaphalocrocis medinalis GUENEE, were investigated by a direct observation in the experimental paddy fields at Chikugo, northern Kyushu. In the field of early-planting culture, young instar larvae began to appear at the end of June and the larval density of the 4th and 5th instars reached 0.75 per hill in early July. Thereafter, the density was very low level until harvest. In the field of normal season culture, the larvae were observed from mid-July and their population densities of the 4th and 5th instars increased gradually, reach-ing a maximum of 0.23 per hill at the end of August. The larval density decreased gradually from early September and only a few larvae were found just before harvest, early November. It seemed that the generations overlapped each other later than August, since various instars of the larvae were observed in a field at the same time. There were distinct peaks of adults occurrence : one peak in early-planting culture in mid-July and two in normal season culture in early August and late September. Two hymenopterous parasites were observed infesting larvae of the pest. The highest percentage parasitism of Trathala flavo-orbitalis was 30.3 % in early-planting culture in early July, while that of Apanteles sp. was 12.5 % in normal season culture at the end of August.