Estimation of monitoring range of sex pheromone trap for the rice stem borer moth, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae) by male head width variation in relation to two host plants, rice and water oats.
The monitoring range of a sex pheromone trap for Chilo suppressalis was evaluated in Gifu, Honshu, Japan, using the bimodal distributions of male head width. The distribution of male head width in both flight seasons was a combination of the 2 normal distributions. The larger one was shown to be from males that fed on water oats (Zizania latifolia [Z. caduciflora]) during the larval stage and the smaller one was that of males that fed on rice plants (Oryza sativa). Males emerging from water oats were caught by pheromone traps set at 6 locations near a water oats population (<250m) at a higher rate in the 2nd flight season than in the 1st. The reverse relationship was observed at 5 other locations (>250m). The results suggested that the monitoring range of a sex pheromone trap for this species is narrower in the 2nd flight season than the 1st one, probably because of competition between wild virgin females and synthetic sex pheromone.