Abstract
Experiments were made to know the relation between the body fluid of the paddy borers and the yellow muscardine fungus. Overwintered larvae of the rice stem borer and paddy borer were infected with spores of the yellow muscardine fungus by means of inoculation and injection and the hyphal growth was observed 20 hours after infection at 25°C. The hypha growth was hastened as the larvae near to pupation, and the length of hypha grew significantly longer after March, although the diameter of the spermatocyst did not change until May. Further the hyphal growth in relation to the weight of the overwintered larvae was also examined. It was observed in case of rice stem borer that the heavier the weight of the larvae, and in case of paddy borer the lighter the body weight, the longer the hypha and the larger the spermatocyst as well as the testis.
It was also confirmed in the first generation larvae of both species that the hyphal growth of the yellow muscardine fungus became faster as the larval inster advanced. A comparative test with various muscardine fungi other than the yellow muscardine did not reveal such definite results.
These results seem to show that the high susceptibility of overwintered larvae to the fungus near to pupation is controlled mainly by their humoral condition.
The authors believe that the number of moths in the first generation which is much controlled by the yellow mascardine fungus, is possibly forecasted by measuring the susceptibility of the overwintered larvae to this fungus.
