Carabid feeding guilds in Midwest watermelon surrounded by corn and their response to pest management practices

Beetles in the family Carabidae are common generalist predators found in Midwest agroecosystems. In a field trial designed to evaluate conventional vs integrated pest management practices as treatments in watermelon production, a diverse assemblage of carabids that included 7800 adults representing by 60 morpho-species, 29 genera, 16 tribes and 6 subfamilies was recorded from watermelon and the surrounding corn using biweekly pitfall traps over a two year period. Six species accounting for more than 90% of the carabid beetles sorted into carabid feeding guilds represented by omnivorous Harpalini (49.8%), mostly predaceous Pterostichini (24.4%) and predaceous Bembidiini (23.1%). Total carabid counts were similar between crops with more Harpalini and Pterostichini from corn and more Bembidiini from watermelon. Carabidae and Pterostichini counts were significantly greater in IPM and untreated plots across crops, but varied with location, season and year. Counts of Bembidiini and Harpalini were similar between treatments, but varied with season by crop. Ordination revealed distinct carabid assemblages between crops, but not between treatments. Carabid taxa/feeding guilds generally corresponded positively with cucumber beetle pests and non-pest prey between adjacent crops as expected of generalist predators operating locally. Overall, the mostly predaceous Pterostichini were more affected by pest management practices than were the omnivorous Harpalini and predaceous Bembidiini in this agroecosystem. This study demonstrates how IPM enhances carabid beetles in watermelon and the surrounding corn as part of the generalist predator community responsible for biocontrol services that help keep cucumber beetle pests below action thresholds.