Linking habitat management and conservation biocontrol through gut-content analysis

Authors: SZENDREI, ZSOFIA - Michigan State University; BRYANT, ALEXANDRIA - Michigan State University; Rowley, Daniel; FURLONG, MICHAEL - Queensland University - Australia; SCHNIDT, JASON - Michigan State University; Greenstone, Matthew

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2013
Publication Date: 8/15/2014
Citation: Szendrei, Z., Bryant, A., Rowley, D.L., Furlong, M., Schnidt, J., Greenstone, M.H. 2014. Linking habitat management and conservation biocontrol through gut-content analysis. Biocontrol Science and Technology. 24:1425-1438.

Interpretive Summary: Traditional insect pest management is heavily dependent on chemical insecticides, with consequent negative impacts to the health of people, livestock, and the environment. Conservation biocontrol, which uses modifications to cropping systems to increase the number of naturally occurring beneficial insects that attack insect pests, can reduce the use of chemical insecticides. It has been shown that increasing the amount of vegetative cover within a crop field can provide beneficial insects with hiding places and refuges from extreme temperatures. We performed an experiment in which the amount of vegetative cover between crop rows in a cabbage field was varied by planting cover crops at different times. We then collected predators and determined whether they had fed on cabbage pests by testing them by PCR for the presence of pest DNA. We found that one group of very important predators, the lady beetles, was most abundant in parts of the field that had the greatest amount of vegetative cover. Also, the predators collected from these parts of the field were most apt to test positive for the remains of one pest, the diamondback moth, which is the most important pest of cabbages and related crops worldwide. Our results show that increasing the amount of vegetative cover within cabbage fields has the potential to increase the abundance and effectiveness of predatory insects in this crop, and thereby to improve pest management in an environmentally safe and sustainable manner.

Technical Abstract: Increasing the habitat diversity of agricultural fields can lead to more effective biocontrol of arthropod pests. Annual cropping systems are exposed to frequent disturbance and lack habitat diversity; therefore it is important to develop strategies that can improve ecosystem services such as biocontrol. One way to increase habitat complexity within the field and provide refuge for predators is to leave cover-crop mulches between crop rows. In our experiment, different gradients of row-middle habitat complexity were created in a cabbage field by manipulating the planting dates of cover crop mulches and reducing herbicide inputs. We used molecular gut-content analysis to determine the impact of habitat management treatments on biocontrol efficacy with species-specific primers for Plutella xylostella (Lepidoptera: Plutellidae) and Pieris rapae (Lepidoptera: Pieridae). In each treatment plot, we counted the number of P. xylostella and P. rapae on cabbage leaves and hand collected predators from the cabbage plants. The abundances of the two herbivore species were not impacted significantly by our habitat treatments, but some ladybeetle species were more abundant in the high-habitat-complexity treatments. About 30% of the predators tested were positive for prey DNA. In particular, the gut-content analysis revealed that predators in our system are not specializing on either prey species, that more complex habitats enhance the rate of predation on P. xylostella, and that the predation on P. rapae is positively density-dependent. In summary, we discovered that manipulating predation through habitat management is a viable strategy in this system.