Abstract
Rice-stem-borer (Chilo simplex Butler), the most serious harmful insect in Japan, prospers in this region, especially in her first generation rather than in her second generation, as compared with other regions. Special attention must be paid, therefore, to the control of this insect in her first generation. In this respect, we analyse the problem into several points, varietal resistance, cultivation system, and the insect habits such as egg-laying, larvae intrusion and the course of spreading the damage spheres. In this report, the cause of varietal difference of egg-laying freqnency by rice-stem-borer was investigated and some important reason of attracting borer-moth to rice-plant was detected. (1) Among varieties a definite tendeny was observed in regard to the frequency of egg-laying on rice-plant, including several nursery conditions of different levels of application of nitrogenous fertilizer. (2) It was recognized that varieties on which more egg-batches were layed, exudated larger quantity of dew drops on the edges of leaf-blades, the dew drops being larger or more quickly formed. The quantity of exudation was studied more precisely in every one hour throughout the night by gathering drops with injecters. It was observed that the number of egg-batches layed, is closely related with the quantity of exudation at night, especially in the forenight. And it was ascertained that the exudation contained a small quantity of ammonia. (3) It was supposed that borer-moth is attracted to rice-plant, in the main, chemotactically; the exudation of leaf-blades containing some substances which attract the moth and, further, the substances will be some N-compounds.
