Nesting habitat enhancement for wild bees within soy bean agricultural fields increases crop production
In an attempt to meet a growing demand for food, the intensification of agriculture is exacerbating a global decline of bees by eliminating semi-natural habitat elements that previously provided floral and nesting resources for bees. Novel experiments with self-pollinating crop species, like soybeans, have revealed a contribution of bees to increased yield. If the presence of bees improves crop yield of self-pollinated species, determining which factors are limiting bee populations in intensified agricultural landscapes should be a key goal of food security research.
To address this question, we experimentally supplemented soybean fields with nesting habitat enhancement strips. Specifically, we investigated (1) bee abundance and diversity measures can be increased through the addition of nesting enhancement strips and (2) higher bee abundance and diversity corresponds to an increase in soybean yield. Four bee predictor variables were tested for their relationship to soybean yield: species richness, functional diversity, abundance and evenness. Bees and soybeans were sampled from paired plots, with one plot comprised of a combined nesting enhancement treatment of an exposed 1mx10m bare soil strip and bamboo bundles and a second control plot of a mesh-covered bare dirt strip. Mesh exclosures were placed over soybeans during bloom to prevent pollinator access.
Linear mixed models with plot as a random effect were used to examine the relationship between bee and soybean variables. Soybean plants open to pollinators had a higher number of pods per plant (χ2 = 6.97, p<0.01), suggesting pollen limitation and a potential benefit of animal pollinators to soybean fruit set. Furthermore, preliminary results show an increasing trend in number of pods per plant (mean ± SE: treatment= 47.9±3.3, control= 43.5±3.5) and seeds per pod (mean ± SE: treatment= 2.679±0.018, control= 2.667±0.014) in plots with nesting enhancement treatments, which corroborates previous reports of inferred soy bean pollination enhancement by bees. Although bamboo bundles were not utilized by cavity nesting bees, we observed bees nesting within the bare-soil enhancement strips. Our findings of reduced soy bean yield in the absence of pollinators and an enhanced yield in the presence of supplemental nesting habitat strongly suggests a mutualism between native ground-dwelling bees and soy bean plants. Nesting habitat enhancements within intensively managed soybean fields may mitigate declines in bee diversity and pollination services while benefitting soybean production.