Abstract
Numerical records of Chilo suppressalis which were caught by light traps located in the Hokuriku district were studied from the viewpoint of population ecology. On massive occurrences, the species often assumed gradation-like processes of multiplication as pointed out by ISHIKURA (1951), although there were also cases of the burst type of outbreak defined by MIYASHITA (1963). In this district, there was neither distinct tendency for simultaneous occurrence of outbreaks nor tendency for centrifugal progress of outbreaks. There was a pretty conspicuous tendency in the western part of the district that the long-term population trends in the first and second generations were similar to each other in a same locality. In some light-trap stations, long successions of extraordinarily high or low female ratios were observed. It was characteristic of these cases that the successions appeared restricted to either of the two generations. This seemed to suggest any long-term sex-related influences of environment exerted on either generation alone.
