Parasitism of Aphids in Canola Fields in Central Oklahoma1

Three aphid species (Hemiptera: Aphididae) typically infest winter canola, Brassica napus L. (Brassicales: Brassicaceae), fields in central Oklahoma. They are the turnip aphid, Lipaphis pseudobrassicae (Davis), the cabbage aphid, Brevicoryne brassicae L., and the green peach aphid, Myzus persicae (Sulzer). The expansion of canola acreage in Oklahoma and the ubiquitous nature of aphid infestations in the crop indicate the need to understand the role of natural enemies in controlling aphid infestations. This study determined the parasitoid species attacking aphids in canola during the flowering through pod development growth stages, when aphid populations often build to the point requiring insecticide treatment. Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae) was the dominant parasitoid species. Individuals of all three aphid species were parasitized by D. rapae. Percent parasitism ranged from 0 to 45% depending on aphid species, field, and sample date. An Aphelinus sp. (Hymenoptera: Aphelinidae) was recovered from cabbage aphids from one field on a single sample date. Parasitism of turnip aphid on 20 May 2013 (17–45%) was greater than parasitism for cabbage aphid (2–12%) on that date. Parasitism of green peach aphid was not significantly different from that of cabbage aphid. Parasitism of cabbage aphid and green peach aphid initially increased but then decreased over the course of the study, while parasitism of turnip aphid continued to increase over time.