Comparison of carabid densities in different cover crop species in north Florida

Abstract

Many ground beetle species (Coleoptera: Carabidae) prey on noctuid larvae and pupae. Therefore, agricultural practices that maintain or even enhance carabid populations have the potential to reduce noctuid pest populations through predation. One such pest is the fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), a migratory pest of row, turf, and vegetable crops. Before migrating in spring from southern Florida and southern Texas, it feeds and develops on cover crops such as field corn and sorghum-sudangrass and expands its populations. Here we sampled the species and density of carabid populations that were active in cover crops with differing capacity to support fall armyworm development. Three cover crop species, sorghum-sudangrass, cowpea, and sunn hemp, were previously studied for their effects on fall armyworm populations, with sunn hemp showing high incompatibility with fall armyworm development. The cover crops were grown in 3 locations in north and north-central Florida and pitfall traps were used to compare numbers of carabid beetles caught in different cover crop treatments. Almost 2,000 predatory and omnivorous carabid beetles were collected. Three species in particular, Calosoma sayi Dejean, Tetracha carolina (L.), and Cicindela punctulata Olivier, are known predators of S. frugiperda in the laboratory and may aid in the reduction of populations in the field. There were no differences in beetle numbers among cover crop plants. In another trial, more beetles were collected in plots of a popular sunn hemp cultivar developed in the southeastern U.S., ‘AU Golden’, than in plots of another germplasm line, Tillage Sunn™. Further research should determine if the predatory species found in this study prey on S. frugiperda in the field and if this added mortality helps reduce crop damage.