Strategic Farming: Let's talk crops discussed pollinators

By Liz Stahl, Extension Educator – Crops, and Dan Cariveau,Associate Professor, UMN Bee Lab

Andrew's cellophane bee (Colletes andrewsi).
Photo: Heather Holm

Pollinators play a critical role in food production. According to the USDA Farmers.gov website, more than 80 percent of the world’s flowering plants need a pollinator to reproduce. Since most of our food comes from flowering plants, we need pollinators too. Pollinators are also a key part of the food web, and they play a role in contributing to soil health and water quality by helping foster robust plant communities. It is estimated they provide ecological services valued at $200 billion each year.

Dramatic drops in bee populations and other pollinator species across North America have raised alarms. On the February 4 Strategic Farming: Let’s Talk Crops program, Dan Cariveau, Associate Professor with the University of Minnesota Bee Lab, along with moderator Claire LaCanne, UMN Extension educator in crops, discussed pollinators and how we can promote them on an agricultural landscape.

Bees have been buzzing around for a long time

Dr. Cariveau discussed that although bees have been found in the fossil record dating back 65 to 75 million years ago, scientists have determined the first DNA from bees likely dates back to around 123 million years ago. Around this time flowers started evolving too. Today, flowers and bees are closely linked, with bees being a critical pollinator of flowers.

At least 20,000 species of bees have been identified across the world. When talking about bees, many people think of the honey bee, but they are just one bee species. MN alone has about 525 species of bees, ranging from tiny species you can just see with the naked eye to very large bumblebee species (Portman et. al.)

Cariveau’s lab specializes in native bee species. Many of these are considered ground-nesting bees (about 80%), as they nest in the ground. Others next in cavities, such as in the hollow stems of plants. While honey bees are very social, other bees are solitary. Although there is much diversity among bees, one thing remains constant, and that is that bees rely on flowers for all of their life cycle.

How are bees doing?

Although this is a common question, it is not an easy one to answer. Cariveau describes this being like asking a botanist how plants are doing or an ornithologist how birds are doing. For one thing, it depends on the species. The rusty patch bumblebee, for example, used to be relatively common across much of the northeastern U.S. and Upper Midwest. Now it is all but extinct over much of its old habitat, being found in just a few locations including in MN, and it has been listed on the Endangered Species list since 2017.

Bees are sensitive to loss of habitat, changes in climate, and disease. Loss of habitat is a key factor his lab and many others in conservation have been focusing on. Bees need food (flowers) and nesting resources to lay their eggs so creating and restoring habitat is critical if we want to help increase and support their numbers.

Restoring habitat on an agricultural landscape

Restoration of habitat can be done in various ways. The cost of restoration will depend on whether or not land needs to be rented or purchased, the preparation and seeding process and the maintenance needed of the planting. There are various sources of funding from conservation groups and programs that may assist growers in helping with the costs of establishing and maintaining pollinator habitat.

One concern about restoring habitat on an agricultural landscape is that native species may not be able to find the habitat if there is primarily agricultural ground around the restored area. Cariveau’s research team found that the amount of agricultural ground surrounding an area did not seem to influence the number of bee species present. The floral resource richness (the number of different flower species on the landscape), however, enhanced the number of bee species present (Lane et al.) This means that we can successfully establish habitat for bees as long as we have a strong flowering community.

Additional research with bumblebees compared the effect of lower-quality conservation reserve program (CRP) mixes (a limited number of plant species) and high-quality CRP mixes (more diverse and more expensive) to a remnant prairie site. They did not find a statistical difference in the number of bumblebees or the number of bumblebee species present across the sites. This tells us that both CRP mixes did a good job in supporting bee species. The number of bees and bee species present, however, was correlated to the number of flowers. This means, as you get more flowers, you get more bees.

Restoring habitat doesn’t have to break the bank

Research conducted across SW MN looked at the impacts of the amount of natural habitat surrounding a planting, size of the pollinator habitat (2 acres compared to 11 acres), and species diversity (the cheaper 8 species mix was about 1/8 the cost of the 40 species forb mix) on native bees. They found that bee diversity and bee abundance was not impacted by the type of seed mix used, or the amount of natural habitat that surrounded the restored areas. As long as flowers were present, the bees came. Bee populations also increased over time while the habitats were in place. This means that rather than spending a large amount of money on a highly diverse mix for a single restoration area, more areas could be planted with a less diverse, less expensive mix that produces flowers, resulting in greater habitat areas across the landscape (Chase et al).

When asked about habitat size, Cariveau indicated that smaller habitats will favor smaller bee species and larger habitats will favor larger bees (as they need larger areas to sustain their food needs). The bottom line is that any size of habitat, including a flowering garden, will provide habitat for bees.

Impacts on crop pests and natural enemies

University researchers have studied soybean fields adjacent to pollinator habitat areas. Results showed that pests did not spill over into the soybean field from the habitat. There was also limited spillover of predators into the field, although they found more natural predators in the pollinator habitat than locations further away in the field.

It was also noted that although soybeans are a self-pollinating species, a summary of research published by Iowa State University found that wild bees and honeybees can improve soybean yields up to 20% when they are around to help pollinate soybeans (Garibaldi, et. al, 2021).

Watch a recording of the full program at the Strategic Farming YouTube channel.

Thanks to the Minnesota Soybean Research and Promotion Council and the Minnesota Corn Research and Promotion Council for their support of this program.

Sources

Chase M, Portman Z, Lane I, Herron-Sweet C, and Cariveau D (2025). Pollinator plantings in the intensively farmed Midwest (U.S.A.) support a core set of common bee species, regardless of local and landscape controls. Restoration Ecology. 33. 10.1111/rec.70175.

Garibaldi, LA, Schulte LA, Nabaes Jodar DN, Gomez Carella DS, and Kremen C (2021). Time to Integrate Pollinator Science into Soybean Production, Trends in Ecology & Evolution, Volume 36, Issue 7, Pages 573-575, ISSN 0169-5347.

Lane IG, Herron-Sweet CR, Portman ZM, Cariveau DP (2020). Floral resource diversity drives bee community diversity in prairie restorations along an agricultural landscape gradient. J Appl Ecol. 57:20102018. https://doi.org/10.1111/1365-2664.13694

Portman Z, Gardner J, Lane I, Gerjets N, Petersen J, Ascher J, Arduser M, Evans E, Boyd C, Thomson R, and Cariveau D. A checklist of the bees (Hymenoptera: Apoidea) of Minnesota (Zootaxa 5304) 95 pp.; 30 cm. 16 May 2023 ISBN 978-1-77688-798-9 (paperback) ISBN 978-1-77688-799-6 (Online edition) 95 pp.