Developmental sensitivity to nicotine as a post-zygotic barrier to reproduction between incipient species of the parasitic wasp, Cotesia congregata

Specialist herbivores and, in turn, parasitic wasps that attack them, have adapted counter defenses to alleochemicals that evolved to deter herbivory. We tested the hypothesis that developmental responses of two incipient species of the gregarious endoparasitoid, Cotesia congregata (Say), to nicotine (0, 0.1 and 0.3%) in the host diet would differ with respect to host-plant complex origin, and elucidated patterns of Mendelian inheritance for nicotine resistance using reciprocal hybrid crosses. Data included the number of egressed and unegressed larvae, cocoons, and emergent adult wasps for each wasp cohort resulting from a single oviposition. Wasps originating from the solanaceous specialist, Manduca sexta L., on tobacco (“MsT wasps”) responded to dietary nicotine in a dosage-dependent manner.  In contrast, wasps originating from Ceratomia catalpae Boisduval, which feeds exclusively on catalpa (“CcC wasps”), had high mortality when exposed to 0.1% nicotine. Responses of the hybrid crosses varied with respect to maternal wasp source. For example, when exposed to 0.1% dietary nicotine, most haploid males with CcC mothers failed to egress from hosts, whereas diploid females from either cross did. Results indicate that nicotine tolerance is a dominant heritable trait or suite of traits.