Quantitative Study of Aphid Natural Enemies in Central Oklahoma Canola Fields

Winter canola (Brassica napus L.) is planted in late September through October in central Oklahoma and harvested in June. Three aphid species typically infest canola fields in central Oklahoma: cabbage aphid, Brevicoryne brassicae L.; green peach aphid, Myzus persicae (Sulzer); and turnip aphid, Lipaphis pseudobrassicae (Davis). Predatory insects and spiders and hymenopteran parasitoids that prey on aphids are present in canola fields in central Oklahoma. We used a D-vac suction device to sample aphids and natural enemies in a total of 23 canola fields in central Oklahoma in early November and mid-March of three growing seasons. During the three growing seasons, 2.4 to 50.9 aphids were collected per 120 placements of the D-vac sampler per canola field. Diaeretiella rapae (McIntosh) was the most abundant parasitoid, with 0.04 to 5.1 individuals per 120 placements, while Araneae (spiders) were the most abundant predators ranging from 0.35 to 4.9 per 120 placements. Other predators were Chrysopidae, Hemerobiidae, Nabidae, and Syrphidae, with relative density of most taxa increasing from November to March. Correlations of relative density of D. rapae and larval Coccinellidae to aphid relative density were positive and significant suggesting the taxa had a reproductive and/or aggregative numerical response to aphids in canola. D. rapae, Coccinellidae, and perhaps spiders killed the most aphids in central Oklahoma canola fields.