Parasitism of the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), on spring wheat (Poaceae) in southern Manitoba.
Six species of Hymenoptera were found as parasitoids of the Hessian fly, Mayetiola destructor (Say), in the Red River Valley of Manitoba in 2003-2005. These parasitoids were the main cause of pupal mortality. Platygaster hiemalis Forbes and a Homoporus spp. mostly parasitised only first generation Hessian flies. Pediobius eubius (Walker), Aprostocetus zosimus (Walker), Trichomalopsis americana (Gahan), and Panstenon poaphilum Heydon mostly attacked second generation flies. All parasitoid species appeared to be univoltine on the Hessian fly. In 2003-2005, 18-28% of first generation flies and 73-79% of the second generation were parasitized in experimental plots. Parasitism of second generation flies in commercial fields in 2005 was 68-85%. Platygaster hiemalis was the most abundant parasitoid of the first generation and P. eubius of second generation flies. The prevalence of P. eubius was greater than the total of all other parasitoid species at all sites in all years. About 25% of adult parasitoids emerged in August after completing one generation in Hessian flies. This late season emergence occurred for all six species, but was least likely for P. hiemalis. A further 15-35% of all parasitoids died as larvae or pupae. This study is the first documented record of P. eubius attacking the Hessian fly in Canada, of A. zosimus in Manitoba, and of P. poaphilum parasitizing the Hessian fly. Ten species of Hymenoptera are now known to parasitize the Hessian fly in Manitoba.