Floral Attractiveness to Bees in Soybean Varieties

Chia-Hua Lin
Staff Researcher
Reed Johnson

As one of the most widely cultivated crops in the U.S., soybean (Glycine max) can be a substantial floral resource for pollinators. However, soybean is a notoriously unreliable forage for bees because different varieties display different floral characteristics such as nectar production which may change depending on environmental conditions. The objectives of this study are (1) to identify the floral characteristics that influence soybeans attractiveness to bees in a range of varieties grown in Ohio and (2) to evaluate the effect of bee pollination on soybean yield. We surveyed bee visitation rates and measured floral characteristics including flower color, size, nectar production, and nectar sugar concentration in 158 soybean varieties grown in single-treatment plots as a part of the Ohio Soybean Performance Trials. A separate experiment was conducted with a subset of the most and least bee-attractive varieties grown in pollinator exclusion cages with or without enclosed honey bee colonies to assess foraging preferences of honey bees and evaluate yield response to honey bee pollination. We observed a strong variation in bee-attractiveness that is primarily driven by nectar productivity in different varieties. Pollination by honey bees generally increased the production of full bean pods by 2 - 7% compared to caged plants without bees, though no significant effect on total yield was observed. Our long-term goal is to generate comprehensive data on bee-attractive soybean varieties that could help guide planting choices to support local pollinators and maximize benefits to farmers.