Cover crops increase foraging activity of omnivorous predators in seed patches and facilitate weed biological control

Authors: BLUBAUGH, CARMEN - Purdue University; Hagler, James; Machtley, Scott; KAPLAN, IAN - Purdue University

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2016
Publication Date: 7/18/2016
Citation: Blubaugh, C.K., Hagler, J.R., Machtley, S.A., Kaplan, I. 2016. Cover crops increase foraging activity of omnivorous predators in seed patches and facilitate weed biological control. Agriculture, Ecosystems and Environment. 231:264-270.

Interpretive Summary: Numerous species of ground beetles are important predators that often consume both weed seeds and insect pests. Knowledge of their feeding behavior in various habitats is important for predicting their usefulness in pest and weed biological control. An ARS scientist at Maricopa, AZ and scientists at Purdue University used specific proteins to mark food items (weed seeds, fly pupae) that were placed in plots to examine the impacts of plant cover crops on ground beetle populations and feeding preferences. Analyses showed that 19% of the beetles fed on weed seeds, including a species not known for seed feeding, whereas only 8% fed on protein-marked fly pupae. In general, plant cover encouraged ground beetle activity and seed consumption, increasing seed predation by 73% compared with bare plots. These results imply that the favorable microclimate and shelter provided by cover crops may promote biocontrol services by ground beetles. We document direct links between cover crops, ground beetle activity, and seed predation, validating the utility of cover crops as a tool to promote weed biocontrol.

Technical Abstract: Omnivores are important consumers of both weed seeds and insect pests, and habitat provisions like cover crops are suggested to promote their ecosystem services in agricultural systems. However, few studies establish direct links between cover, food, and pest suppression because they are entangled and co-occurring in working agroecosystems. Here, we use immuno-marking to examine both aggregation and consumption by omnivorous ground beetles in response to experimentally manipulated vegetative cover, weed seeds, and invertebrate prey. We found evidence of seed feeding in 19% of individuals, including some species considered largely predaceous, whereas only 8% tested positive for prey. Responses to resource subsidies were species-specific, but vegetative cover generally facilitated omnivore activity and seed consumption, increasing seed predation by 73% compared with bare plots. Early in the season, presence of seeds increased omnivore capture by 77%, but this aggregative response disappeared by autumn in both years of the study. Prey availability never influenced ground beetle aggregation, and cover had no impact on the frequency of prey consumption. These results imply that the microclimate and biological resources associated with vegetated habitat may promote biocontrol via increased omnivore activity density, but only plant-based foods induce predictable effects on foraging behavior. We document direct links between cover crops, omnivore activity, and seed predation, validating the utility of cover crops as a tool to promote weed biocontrol.