Water-oats harbors two strains of the striped stem borer Chilo suppressalis (Lepidoptera: Crambidae) with temporal divergence in mating behavior

The striped stem borer, Chilo suppressalis Walker, is a widespread insect pest in China, which feeds both on rice (Oryza sativa L.) and water-oats (Zizania latifolia Griseb.). The populations collected from rice (rice population, CSR) and water-oats (water-oats population, CSW) were observed for mating behavior. Results showed that the mating rhythm of CSR in scotophase was unimodal distribution, while that of CSW was bimodal distribution. The first mating peak of CSW occurred about 3.5 h after the onset of scotophase, which overlapped well with the single mating peak of CSR. The second mating peak of CSW occurred about 5.5 h after the onset of scotophase. The descendant populations from those three mating peaks were also observed for mating behavior, and the temporal patterns were found to be hereditable. In the second generation, mating rate was abnormally low in crossings between females of the first mating peak and males of the second mating peak. Pupae weight differed significantly between CSR and CSW in the first generation but did not in the second generation reared with the same food in laboratory. Our results indicated population collected from water-oats is mixed population, containing indigenous water-oats feeders and temporary residences from rice field. It was discussed that water-oats acts as a refuge crop to delay the resistance development to pesticides and Bt (Bacillus thuringiensis) rice.