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

Abstract

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 latifolia). 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.

Water ferns Azolla spp. (Azollaceae) as new host plants for the small China-mark moth, Cataclysta lemnata (Linnaeus, 1758) (Lepidoptera, Crambidae, Acentropinae)

“…For example, woolly bear caterpillars (Grammia incorrupta Edwards; Lepidoptera, Erebidae, Arctiinae) that were parasitized by Exorista mella Walker (Diptera, Tachinidae) ingest more of the plant toxins called pyrrolizidine alkaloids to confer increased resistance against parasitoids (Singer et al 2009). Chilo suppressalis (Walker) (Crambidae, Crambinae) that feed on water-oat differ in adult body size and mating time compared with those that feed on rice (Takasaki et al 1969;Ishiguro et al 2006). Perhaps the different colouration of C. lemnata feeding on Azolla spp.…”

Difference in diel mating time contributes to assortative mating between host plant-associated populations of Chilo suppressalis

“…S1). This difference was considered to be an intrinsic feature of each host-associated population and to be independent of sampling time and locality222534.…”

“…The seasonal peaks of emergence the rice population also differ from those of the water-oat population262829. Furthermore, diel mating activity begins earlier in the rice population than in the water-oat population22333435. These differences suggest that the rice and water-oat populations of C. suppressalis are sympatric host-races25293135.…”

“…Indeed, it has been suggested that differences in seasonal emergence and diel mating activity could be important factors contributing to the development and maintenance of reproductive isolation in these two host-associated populations of C. suppressalis 222535. However, because these populations have considerable overlap in the seasonal timing of adult emergence2935, a slight overlap in the diel timing of mating activity223435, and adults can migrate from rice to water oat fields, and vice versa35, there is potential for hybridization. Indeed, viable hybrid offspring have been produced under laboratory conditions22 and may exist in the wild34.…”

“…However, because these populations have considerable overlap in the seasonal timing of adult emergence2935, a slight overlap in the diel timing of mating activity223435, and adults can migrate from rice to water oat fields, and vice versa35, there is potential for hybridization. Indeed, viable hybrid offspring have been produced under laboratory conditions22 and may exist in the wild34. Therefore, both the degree of assortative mating between these two host populations, and the importance of inter-population differences in diel mating time to this, remain unclear.…”