Do differences in life‐history traits and the timing of peak mating activity between host‐associated populations of Chilo suppressalis have a genetic basis?

Abstract

The development of host races, genetically distinct populations of the same species with different hosts, is considered to be the initial stage of ecological speciation. Ecological and biological differences consistent with host race formation have been reported between water‐oat and rice‐associated populations of Chilo suppressalis. In order to confirm whether these differences have a genetic basis, we conducted experiments to determine the extent to which various life‐history traits and the time of peak mating activity of these populations were influenced by the species of host plant larvae were raised on. Individuals from each population were reared for three consecutive generations on either water‐oat fruit pulp or rice seedlings. Descendants of both populations had higher larval survival rates, shorter larval developmental periods, higher pupal weight, and longer adult forewings, when reared on water‐oats than when reared on rice. The time of peak of mating activity differed between the descendants of each population, irrespective of whether they were raised on water‐oats or rice. These results indicate that although some life‐history traits of host‐associated populations of C. suppressalis are influenced by the host plant larvae are raised on, time of peak mating activity is not. Because it is a stable, objective, phenotypic trait, further research on difference in the time of peak mating activity between host‐associated populations of C. suppressalis should be conducted to clarify the mechanism responsible for host race formation in this species.

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

“…These were: (1) to confirm the degree of host-independent, behavioral, partial premating reproductive isolation (mating patterns) between the two host populations suggested by previous studies222535, (2) to determine to what extent divergence in diel mating time contributes to the observed assortative mating of each population. To investigate the mating patterns of the two populations we conducted three kinds of mate choice tests; no choice, single choice (both female and male choice), and multiple choice, throughout the entire scotophase.…”

“…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.…”

“…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.…”

“…Chilo suppressalis Walker (Lepidoptera: Crambidae), is an ideal species in which to investigate whether divergence in diel mating time contributes to reproductive isolation between host populations2225. C. suppressalis is an economically significant pest of gramineous plants, especially rice and water-oats, in the East Asian region222627.…”

“…In this region rice and water-oats are usually cultivated in neighbouring fields, or planted in rotation in the same fields2829 and are the only host plants on which C. suppressalis can complete its entire life-cycle without changing host30. Larvae, pupae, and adults, of C. suppressalis fed on rice plants, or collected from rice fields, are smaller than those fed on water-oat plants or collected from water-oat fields2526283132. The seasonal peaks of emergence the rice population also differ from those of the water-oat population262829.…”