In central Oklahoma, winter canola (Brassica napus L.) has recently become the primary rotational winter crop with wheat (Triticum aestivum L.). Annual aphid pest outbreaks in canola have resulted in widespread application of insecticide. Insect parasitoids, which frequently suppress aphids in nearby wheat, may move to canola because of large numbers of aphids. These parasitoids probably will be exposed to insecticide. Lysiphlebus testaceipes Cresson is the dominant parasitoid of aphid pests in wheat in Oklahoma and can frequently suppress and maintain aphid infestations below the economic injury level. The expansion of canola acreage in Oklahoma might disrupt biological control of cereal aphids in wheat if L. testaceipes prefers to colonize canola because of the abundance of aphids and many die as a result of more frequent use of insecticide in canola. In this case, canola could act as an ecological trap for L. testaceipes. We surveyed aphids and their parasitoids in wheat and nearby canola fields in central Oklahoma approximately at flowering time for canola. The purpose was to determine the relative abundance of aphids and parasitoids in each crop and assess the potential for canola fields to act as an ecological trap for L. testaceipes. For aphids collected from canola fields, Diaeretiella rapae (M'Intosh) was the dominant parasitoid, with rates of parasitism ranging from 2 to 27%. Aphelinus sp. also parasitized the cabbage aphid, Brevicoryne brassicae L., but was rare. Lysiphlebus testaceipes was not recovered from any species of aphid in canola despite being abundant on aphids in nearby wheat fields, with parasitism ranging from 3 to 43%. The results suggested limited potential for canola to attract and potentially serve as an ecological trap for L. testaceipes from wheat.
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Vol. 39 • No. 1