Arthropod Parasitoids and Predators of the Onion Maggot (Diptera: Anthomyiidae) in Southwestern Ontario

Miniature (1 m2) mass-rearing beds containing onion maggot, Delia antiqua (Meigen), were established during 1980 and 1981 at three commercial onion-growing fields and an experimental farm in southwestern Ontario to attract local parasites and predators. Onion maggot (OM) pupae from each of the three generations were collected from the beds before eclosion and allowed to complete development in the laboratory, enabling collection and identification of emerging parasitoids. Seven insect species (three staphylinid, four hymenopteran) were confirmed as parasitoids of OM, of which only Aphaereta pallipes (Say) and Aleochara bilineata (Gyllenhal) were significant mortality agents (parasitism rates up to 17 and 20.7%, respectively). Twenty carabid, 42 staphylinid, and 17 other (total 79) arthropod species of predatory habit were associated with OM in or near the miniature rearing beds. Twenty-one of the 79 species of mooted predators accepted OM eggs, larvae, or pupae as food under laboratory conditions. Diversity of arthropod predators and parasitoids was highest at the experimental farm at London (53 + 7 spp., respectively) > the three commercial onion-growing fields at Thedford (39 + 6) > Keswick (36 + 5) > Bradford (36 + 4).