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A pest monitoring dataset collected for organic Brassica fields in south coastal British Columbia, Canada, was examined to test three possible scenarios explaining poor aphid control by natural enemy insects: the lack of diversity within the enemy guild, slow colonization of fields by enemies, and poor natural enemy reproduction. Both parasitoids and predators were detected, but the predator guild was composed primarily of syrphid larvae and very few coccinellids. We detected a lag in the colonization of fields by enemies: aphids were detected in >20% of samples, but enemies in <5% within 3 weeks of transplanting. Within the first week of transplanting, aphids exceeded the spray action threshold of 10% colonized plants. Although we predicted that Brassica plants located next to field margins would have more parasitism and syrphid oviposition, because of their proximity to floral resources (pollen and nectar) in weeds and shrubs of field margins, the levels of parasitism were equal in both interior and edge plants, and the highest levels of syrphid oviposition activity were observed in plants within fields. These findings suggest that solutions for enhancing biological control of aphids in organic Brassica fields should focus on earlier establishment of enemies within fields, and that aphid control could be enhanced by increasing the diversity of the predator guild, focusing especially on highly mobile predators that are aphidophagous as adults. One possible strategy would be to introduce ladybird beetles on host plants to fields prior to transplanting the crop. [ABSTRACT FROM AUTHOR]

We determined that spinosad interacts synergistically with the biocontrol agent Metarhizium anisopliae (Metch) Sorokin to increase the mortality of two wild-collected wireworm species, Agriotes lineatus (L.), and Agriotes obscurus (L.). Bioassays were performed using a M. anisopliae isolate originally acquired from a local wireworm cadaver. M. anisopliae was applied as a soil drench at 3.3 × 10² and 104 conidia per gram sand, respectively. Soil drenches also were prepared using a commercial formulation of the actinomycete toxins spinosyn-A and spinosyn-D (common name spinosad) at sublethal doses of 1.5,3, and 6 ppm active ingredient per gram sand. Combined treatments of spinosad and M. anisopliae were synergistic in causing mortality for all spinosad concentrations. Wireworm feeding activity was reduced after exposure to both spinosad and M. anisopliae and was found to be concentration dependent. The high mortality and reduced rate of wireworm feeding suggest that spinosad and M. anisopliae treatment combinations should be tested in the field. [ABSTRACT FROM AUTHOR]