Conserving or enhancing floral, alternative prey, or shelter resources has been shown to increase the effectiveness of predatory hoverflies in some agroecosystems. However, it is still difficult to predict just how limited certain hoverfly species are for these resources, what direct and/or indirect effects increasing these resources may have on herbivorous pests or other natural enemies, and how cost effective these manipulations may or may not be for an IPM program. To help determine the usefulness of this tactic for enhancing the potential of predacious hoverflies (Diptera: Syrphidae) to limit cabbage aphid (Brevicoryne brassicae, Homoptera: Aphididae) infestations in commercial broccoli, a series of field, cage, and laboratory trials were conducted to assess: 1) the ability of hoverflies to find and limit cabbage aphid infestations, and 2) the field-scale effect that added flowering plants have on the foraging and oviposition activities of these hoverfly species, along with the relative preference that hoverflies and other key arthropods in the broccoli system have for these floral resources. A few hoverfly species demonstrated the ability to find and reduce cabbage aphid colonies, but they arrived only after an economically unacceptable level of aphid infestation had occurred. Oviposition was greater on infested broccoli closer to blocks of floral resources in the field, but time of season appeared to exert a stronger influence. Hoverfly and key pest herbivore species showed preferences for certain flower types. The overall findings suggest that a landscape perspective may be required to determine the factors that limit hoverfly activity in agroecosystems.
Species 1: Diptera Syrphidae Eupeodes fumipennis (hover fly, flower fly)
Species 2: Diptera Syrphidae Spaerophoria sulphuripes
Species 3: Homoptera Aphididae Brevicoryne brassicae (cabbage aphid)
Keywords: insectary plantings, biological control
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