Genetic differences between rice and water-oat feeders in the rice stem borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae)

The rice stem borer, Chilo suppressalis (Walker) is an important lepidopteran pest of rice plants in Japan, and feeds on both rice (Oryza sativa) and water-oats (Zizania latijblia). We evaluated the difference in mating time of the two feeders under both laboratory and field conditions. The male moth of the water-oat feeders (WF) began to mate 7 h after the beginning of the scotophase, about 4 h later than the peak of mating of the rice feeders (RF). In accordance with this result, the body size of males trapped using synthetic sex pheromones differed between the two trap periods (sunset to 1:00 am vs. 1:00 am to sunrise) in the field, suggesting that the rice feeders were trapped earlier than the water-oat feeders. However, there was no unequivocal evidence showing limited gene flow between the two feeders at the level of allozyme polymorphisms. These results suggest that as the two feeders of C. suppressalis have recently diverged, the allozyme loci have not yet diverged to fixation.