Ohio Soybean Fields Are Home to a Surprisingly High Number of Bees

Soybean fields, with their large expanses of uniform green plants, seem an unlikely habitat for bees and other pollinator insects. The tiny white or purple flowers of soybeans are self-pollinated, so they technically don’t need assistance from friendly insects for the seed-development process. These attributes have steered most soybean research projects toward yield-robbing pests like bean leaf beetles, aphids and stink bugs.

Not all research goes this route, however. Kelley Tilmon, an entomologist at The Ohio State University, understands that pollinators play a positive role in soybean yields.

“For many years, people didn’t worry very much about whether there were pollinators in soybeans. However, there is some evidence now that, even though soybeans are self-pollinated, having a good pollinator community might actually enhance yields,” she said.

Tilmon and her colleagues have been working on a multi-year project funded by the Ohio Soybean Council and the North Central Soybean Research Program that investigates the diversity of pollinator insects in soybeans. The results are surprising.

“We’ve found close to 48 different pollinator species in Ohio soybeans. That’s very exciting!” she said.

In addition to identifying pollinators, the researchers wanted to know how deep the insects would forage into a soybean field. Were they simply straying in from neighboring areas or were these pollinators really making an effort to visit soybean fields?

By using a special insect trap called a bee bowl, pollinator insect populations could be monitored on a weekly basis in eight different Ohio soybean fields during the flowering through pod-filling growth stages. The bee bowl, a yellow apparatus that attracts bees with its bright color in order to trap them in soapy water, is mounted on a stake placed at various points in or around a soybean field.

This method proved quite efficient, as Tilmon’s team learned the following:

• Out of all the bee species collected, sweat bees were the most abundant. One particular sweat bee species, Lasioglossum hitchensi, had the highest representation at 36% of all trapped bees.
• The bees that many of us visualize as pollinators, like honeybees and bumble bees, only comprised 3% of the total bee population collected. Of these, Western honey bees composed the highest percentage at nearly half.
• The most pollinators per week were collected during the second half of July and the least in mid-August.
• Regardless of how far into a field the bee bowls were placed – up to 250 meters or 820 feet from field edge – the numbers of bees collected were nearly identical. This suggests that soybeans are a significant habitat for pollinator species.

Bee Family	Examples	Number collected	Percent of total bees collected
Apidae	Honeybees, bumble bees	81	3.0%
Colletidae	Plasterer bees	15	0.6%
Andrenidae	Mining bees	4	0.1%
Halictidae	Sweat bees	2,579	96.2%
Megachilidae	Leaf cutter bees	2	0.1%

Now that Tilmon has a good idea of the pollinator diversity within Ohio soybeans, phase two of the project will help determine the time of day when these insects are most active. This information will then be distributed to farmers interested in adjusting their insecticide applications to maintain healthy bee populations for a potential yield bump. Additionally, even if pollinator-associated yield increases aren’t drastic, preserving strong bee populations is still rewarding.

“It’s nice for soybean farmers to know that their soybean fields are contributing to pollinator health and the ecosystem,” Tilmon said.

Read full survey results from 2018 research and learn more about checkoff-supported insect research happening in Ohio fields.