INVESTIGATIONS ON THE NATURAL ENEMIES OF THE RICE STEM BORER, : CHILO SUPPRESSALIS ESPECIALLY THE YELLOW MUSCARDINE FUNGUS, ISARIA FARINOSA.

Abstract

It is generally reported that the yellow muscardine fungus, Isaria farinosa, is supposed to be the most important factor for environmental resistance against the overwintering rice stem borer, Chilo suppressalis. The writer attempted to make quantitative investigations on the relative effectiveness of the larvae to the controlling factors. Two heaps of rice plant straws in which overwintering larvae inhabited were used for study ; one was placed on a paddy field and the other in a barn. In the former heap, the yellow muscardine, which was prevalent in late spring or early summer, was found to be an important cause of the mortality of larvae, while those killed by hymenopterous parasites were almost as large in proportion. As for the heap in the barn the number of dead larvae caused by this fungus was much less than in the case of the former. Besides these two controlling factors, the dead larvae of which causative agent was not elucidated were considerably included in both heaps. Attention must be paid to the fact that the numbers of such dead larvae were no less than those by the yellow muscardine or hymenopterous parasites. Isaria infections were not found among the larvae feeding on the stem of the rice plant growing on a paddy field.