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 treatment, in-furrow pyrethroid, and
untreated plots at three farms in Maryland for three 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 and injury did not
translate to differences in yield. The in-furrow pyrethroid 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.