Host location and parasitism of Brevicoryne brassicae in diversified broccoli cropping systems

Host location is a crucial step in the life cycle of the cabbage aphid, Brevicoryne brassicae (L.) (Homoptera: Aphididae). Diversified cropping systems have the potential to inhibit or interfere with host location processes to reduce the severity of aphid outbreaks. We altered the vegetation mix of a broccoli [Brassica oleracea var. italica (Plenck) (Brassicaceae)] cropping system by substituting broccoli with strips of potatoes [Solanum tuberosum (L.) (Solanaceae)], planting broccoli into a cereal rye [Secale cereale (L.) (Poaceae)] cover crop, or both. The probability of aphid infestation was significantly reduced by the presence of the cover crop, whereas strips of potatoes slightly increased initial numbers. The effectiveness of the cover crop treatments was primarily due to fewer alate aphids initially colonizing broccoli plants. Aphid parasitism by Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) did not explain the observed differences in the number of aphid colonies present in each treatment.