Turfgrass covers more than three times as much land area as any other irrigated crop in the United States and has an annual industry value greater than that of corn and soybeans combined. Bluegrass billbugs (Coleoptera: Curculionidae) are a serious pest of turfgrass. These weevils feed on stems, roots, and crowns of the plant, causing severe discoloration and plant death. Currently, billbugs are almost exclusively managed with preventative applications of systemic, long-residual insecticides. Largely due to the cryptic nature of the damaging larval form, these applications occur before turf managers know if billbugs will cause significant damage in a given year or in a given area. Relatively little research has focused on how the diverse predatory arthropod community that resides in turfgrass —including multiple ground beetles (Coleoptera: Carabidae), rove beetles (Coleoptera: Staphylinidae), spiders (Arachnida: Araneae) and ants (Hymenoptera: Formicidae)— may be used as a tool for billbug suppression. Though very low rates of direct consumption by these predators have been recorded, work in other systems suggests that the non-consumptive effects of predator presence (e.g. reduced oviposition rates) can significantly impact overall fitness of potential prey. In a series of behavioral assays, we quantify the behavioral changes resulting from the presence of arthropod predators. To further identify the drivers of non-consumptive effects, we also characterize billbug behavior when they are exposed to different cues associated with predator presence (e.g. visual or chemical cues).
Results/Conclusions
We found significant behavioral differences between billbugs exposed to predators and those in the predator-free control. Furthermore, exposure to predator communities with greater species richness elicited behavior that differed significantly from the single predator species condition. These results add to the body of evidence suggesting that, though predators do not significantly contribute to billbug control via direct consumption, supporting a healthy and diverse predator community may still contribute to suppression. Positive controls suggest that both visual/vibrational cues, as well as chemical cues are responsible for the differences in behavior we observed in the predator treatments. Understanding of these cues can aid in the development of more sustainable methods of control, such as employing pheromones and kairomones coupled with targeted pesticide sprays. In many systems these techniques have been extremely successful in reducing pesticide input while still achieving adequate pest suppression; and, turfgrass shows promise as a system in which such techniques could be effective as well as beneficial to ecosystems and humans alike.