Predicting slug injury in corn and the role of carabid natural enemies in regulating slug populations

While integrated pest management and biological control may be valuable approaches to managing slugs in field corn, their use is complicated by unclear thresholds and extensive use of preventative insecticides, as well as confusion regarding what predatory species contribute to biocontrol. To better understand slug injury and biocontrol in field corn, we conducted a comparison between neonicotinoid seed treated, in-furrow pyrethroid (IFP) treated, and untreated plots at 3 farms in Maryland for 3 years, measuring slug activity-abundance, seedling injury, yield, the predator community, and predation on sentinel prey. To clarify links between native predatory carabid species and the native slug Deroceras leave Müller, we tested whether D. laeve detected and avoided full-body extracts of Chlaenius and Poecilus species in laboratory bioassays. In the field, slug activity-abundance did not explain seedling injury or establishment, nor did slug injury correspond to yield. The IFP reduced activity-abundance of predatory beetle larvae, but neither insecticide disrupted adult carabids or predation. Correspondingly, slug activity-abundance and injury were unaffected by treatments. However, predatory species, especially Chlaenius tricolor Dejean, were present across site-years and predation was comparable to previous studies. Further informing the role of C. tricolor, D. laeve avoided the cues from C. tricolor in the bioassay, suggesting a key role in slug biocontrol. In conclusion, while predicting slug risk remains difficult, our results highlight the potential of biological control and suggest that using at-planting insecticides more sparingly may lead to more robust predator communities.