Why do carabids love cover crops? Isolating mechanisms of generalist predator recruitment in agricultural systems

Cover crops are widely used as cultural controls of weeds in annual vegetable crop systems, and may also enhance biological control services by generalist predators by providing diverse food resources, shelter from the elements, and refuge from predation.  Recent work has emphasized that omnivory is nearly ubiquitous among carabids (Coleoptera:Carabidae), and many species in the family may respond to both seed and insect prey resources in the field.  To isolate the effects of biotic and abiotic factors that affect carabid recruitment and feeding behavior, we controlled vegetative cover, cultivation disturbance, and both seed and prey food resources.  Ground beetles were sampled in barrier-linked pitfall traps in structurally simple (i.e. untilled bare soil) or structurally complex (i.e. red clover, Trifolium pratense) plots at 12, 24, and 120 hour intervals for 6 weeks following food resource subsidy treatments in the spring and fall.  The carabid community was characterized by Poecilus chalcites (predator), Pterostichus melanarius (omnivore), Harpalus pennsylvanicus (omnivore), and Anisodactylus sanctacrucis (omnivore).  Recruitment responses to cover crops often vary between omnivores and predators, and this effect may be linked to food resource availability and foraging strategy.  Quantifying and disentangling these biotic and abiotic factors will enhance knowledge of the ecology of carabid predators, and better inform strategies for conservation biological control.