Can conserving insect pollinators increase seed production for soybean?

In cultivated soybean, Glycine max (L.) Merr., pollen is shed directly onto receptive stigmas before flowers bloom resulting in high rates of self-pollination. Despite self-pollination, soybean possesses flowers capable of out-crossing. Insect pollination can increase seed set and yield in soybean, but the benefits are inconsistent across cultivars and growing conditions. It is not clear if efforts to conserve pollinators through the addition of floral resources contribute to the pollination of soybean. In July of 2012, we conducted an experiment in Boone County, Iowa, to assess the contribution of insect pollinators of soybean within habitats with varying amounts of floral resources. These habitats have been shown to produce significant variation in the diversity and abundance of insect pollinators. A male-sterile, female fertile variety (Genetic Type Collection Number T359H, Gene symbol ms9) was used to measure insect-pollination of soybean. We hypothesized that male-sterile soybean plants within habitats having greater species richness and diversity of pollinating insects would have greater seed-set than male-sterile plants within habitats having lower pollinator richness and diversity. Six habitats were assigned to 2m by 2m plots within a randomized complete block design with four replications. At anthesis, potted male-sterile, female-fertile soybean plants were placed within each habitat, along with potted male-fertile siblings as pollen donors. Half of these potted plants were caged to assess the contribution of insect pollinators to seed set. Pollinator communities were sampled using blue, white, and yellow colored bee-bowls. At harvest, each male-sterile plant was threshed, and the number of seeds recorded.