An Analytical Study on the Injury to Rice Plants by the Rice Stem Borer, Chilo suppressalis WALKER (Lepidoptera : Pyralidae) in Its First Generation

The emergence and spread of the injury to rice plants by Chilo suppressalis in its first generation were studied in Takada, Niigata Prefecture, in 1965 and 1966. In the former year, the injury which was regarded as being caused by borers originated from a single egg mass was analysed. The injury did not spread concentrically from the hill of rice plants on which the larvae had hatched. More complicated methods of analysis were necessary for the data obtained in 1966 than for those in the preceding year, because clusters of injured plants of different origins existed often overlapping one another. MORISHITA'S Cδ-index was available for indicating the intensity of the overlapping of clusters between two research dates. The tendency was detected that the extent of convergence was lower in the distribution of clusters which appeared on June 10th or so than in the distribution of those which appeared near the end of that month.