Cover crop diversification can interfere with pest suppression by key generalist natural enemies

Agronomic croplands are often highly disturbed and lack alternative resources to support generalist natural enemies. The introduction of floral resources into these farmscapes represents a conservation biological control approach that can support natural enemies through the provision of nectar and pollen. Natural enemies often exhibit preferences toward specific plant species; therefore, insectary plant mixtures may be able to be designed to target specific natural enemies. We established insectary cover crop plantings of buckwheat (Fagopyrum esculentum), which provides floral resources, and cowpea (Vigna unguiculata), which provides nectar through extrafloral nectaries. These cover crops were grown in mono- and bi-culture treatments. To measure the impacts of these mono- and bicultures on arthropod communities, we sampled insects weekly via sweep net and assessed predation with sentinel egg masses of the European corn borer, Ostrinia nubilalis.  Preliminary results suggest increasing predator abundance in the cover crop treatments over time and with increasing density of cover crop flowers. The buckwheat and buckwheat-cowpea mixtures were highly attractive to several natural enemies including spotted ladybeetles (Coleomegilla maculata), minute pirate bugs (Orius spp.), and crab spiders (Araneae: Thomisidae) as suggested by their higher abundances compared to the cowpea monoculture treatment. However, despite higher abundances in treatments containing buckwheat, predation on sentinel eggs remained low. In addition, cowpea monoculture treatments attracted potato leafhoppers (Empoasca fabae), a pest of legume crops. Our results emphasize the importance of screening insectary plants for their impacts on beneficial and pest insects, and on rates of predation.