Differences in timing of the emergence of the overwintering generation between rice and water-oats populations of the striped stem borer moth, Chilo suppressalis (Lepidoptera: Crambidae)

The striped stem borer moth, Chilo suppressalis, consists of two host-associated populations: a rice-feeding population and a water-oats-feeding population. We investigated the seasonal occurrence of each population using sex pheromone traps in paddy fields and adjacent water-oats vegetation. Trapped males were individually classified into their respective populations by morphometric analyses of genitalia. Although the first flight of the water-oats population was long, with 1 to 3 poorly resolved peaks during April to June, that of the rice population was much shorter, with a sharp peak in early June. This result supports previous observations that adults of the overwintering generation of the water-oats population occur about two months earlier than those of the rice population; however, it is uncertain how this difference enhances reproductive isolation between the two populations because the occurrence overlaps.