Optimizing buffer strips for insect-derived ecosystem services

Plant diversity is an important factor when determining the diversity of organisms at higher trophic levels, including insects that mediate ecosystem services. Organic farms are required to establish and maintain vegetative buffer zones to mitigate pesticide and GM crop pollen drift from neighboring, conventional farms. However there are few guidelines regarding the species composition within these buffer zones. Our objectives are to identify combinations of plants that provide beneficial insect communities with a perennial habitat that provides nutritional resources. From a survey of organic farmers in Iowa, we determined that most buffer strips are composed of grass species; creating a simple, homogeneous environment with limited resources for beneficial insects. We hypothesize that buffers with a combination of plant species, shown individually to attract beneficial insects, will enhance beneficial insect abundance more than a single species. We assessed the insect communities found in replicated, small (2m²) plots that included mixes that ranged from 2 to 12 species of native perennial forbs and grasses. These species were determined attractive to natural enemies and native pollinators. We compared these treatments to plants commonly found in buffer strips: non-Bt corn; Zea mays L., alfalfa; Medicago sativa L., switchgrass; Panicum virgatum L. and corkscrew willow; Salix matsudana Koidzumi. Insects were collected during the first and third week of June, July, and August. Collection methods conducted at each plot: include yellow sticky card traps centrally positioned for a period of five to seven days and timed, 30 second, mid-day, foliage vacuuming using a modified leaf-blower.