Investigation of pre- and post-zygotic reproductive barriers between two host-plant complex races of the parasitic wasp Cotesia congregata (Say) [Hymenoptera: Braconidae]
Investigations of host-associated differentiation of parasitoids have largely focused on the degree of molecular genetic differentiation, but a true test of species status must examine the mating patterns of differentiated populations to determine if they can interbreed in the wild and produce viable offspring. We examined possible mechanisms of isolation between two genetically distinct host-plant complex races of the braconid, Cotesia congregata, originating from hosts on tobacco and catalpa. We compared male responses to female pheromones, elements of male acoustic courtship signals, and breeding success between the two races. Males responded to pheromones from both sources and male courtship signals showed only subtle differences, suggesting that factors other than courtship behavior may be involved in isolation of the two races. However, nearly 90% of females from one hybrid cross failed to produce offspring, leading to post-zygotic isolation. Development time, emerged brood size, and sex ratios between the races also differed
