Interest in pollinator conservation is growing. Not only within academia, but also in a number of disciplines that deal with land management in one way or another. One common theme that unites many of these individual communities involves supporting bees by increasing the availability of flowering plants in the environment. In theory this is great, but in practice, the choices made prior, during, and after the implementation of wildflower habitat can influence which wildflowers persist AND the bee community that visits them. Here, I’ll focus on the “prior”, more specifically, filtering through all of the possible plant species to select the right ones.
It turns out that different bees are attracted to different flowering plants. Considering that there are likely over 465 bee species in Michigan alone (with different diets, body shapes, lifecycles, etc..) this might not be totally surprising. Some bees have long tongues adapted for sipping nectar from long tubular flowers, while others have short tongues that restrict access to nectar in these same plants. Interestingly, diet breadth (or the number of plant species utilized by a bee species) can vary quite considerably between bees. Species of bees that have different diet restrictions (or lack thereof) can respond differently to wildflower enhancement. Generally, increasing flowering plant diversity in a wildflower plot increases the likelihood that some of these more “picky” bees will get the food that they require.
Below are two species of Michigan bees, the bee on top is Andrena gardineri and the bee on the bottom is Bombus impatiens. One of these species is extremely rare in Michigan and only visits plants within a specific genus, while the other is very common and visits just about any flowering plant you can think of. Can you guess which is which*?
Photos by Jason Gibbs
As pollinator conservation becomes increasingly popular, more and more money is being spent on habitat programs while information on plant selection for these programs has remained relatively stable. Granted, most groups putting in wildflower habitat use wildflower seed mixes developed using expert opinion, but how do we know that these mixes represent the “best” plant species for a target bee community? What if the goals of habitat managers are different? Would the plants used in a wildflower mix to support the bees that pollinate a crop like blueberries be the same as plants in a mix to increase bee diversity? These are the questions that keep me up at night.
Luckily, the lab I’m in at Michigan State University has been working on understanding what plants bees like for a long time now. Way back in 2008, Dr. Julianna Wilson (faculty member at MSU) first determined which wildflower species that are adapted for mesic soils in Michigan are most frequently visited by bees. Over the past two years, I’ve been working on a very similar study, but with wildflowers adapted to sandy soils. Together, we’ve generated a list of over 80 plant species and 7000 individual bees, documenting which wildflowers best support bee abundance and diversity. For the sake of brevity, I can’t provide you with all of that information here, but I will share with you two of my main findings:
1. Different groups of bees have clear preferences for wildflower species. For example, the top five plant species visited by bees of two common bee families (Apidae and Halictidae) are mostly unique.
2. Certain floral characteristics seem to be driving the magnitude of wildflower attractiveness. For example, plant species that produce more floral area tend to be more attractive to wild bees than plants that produce little floral area, possibly due to increased pollen availability in these wildflower species.
It turns out that when we use all of this data and fancy computational tools to build wildflower mixes that support particular bee conservation goals (blueberry pollinators vs bee diversity) we get similar but different wildflower mixes.
Flower Mix for Attracting Blueberry Bees
*Green = bloom time of flowers
Flower Mix for Maximizing Bee Diversity
If you look closely, you’ll see that 9 of 15 plant species are shared between wildflower mixes.
So, getting back to this idea of plant selection, or selecting the right plant species to support bees. Most bees like big, showy, and native wildflowers that produce lots of floral area (or is it pollen?), but selecting the right plant species depends on your conservation goals. Selecting a diversity of plant species that have overlapping blooms from May-October will create a habitat that provides food for the bees that are active at different times during the year. Even though there are literally hundreds of flowering plants available at most plant producers don’t be fooled by showy ornamental varieties, as these tend to be less attractive to bees than their native relatives. I can’t tell you exactly which flowers to plant, but fortunately, MSU and others have put together a TON of resources to help guide you through the plant selection process. Last but not least, always shop for locally adapted plant species by purchasing plants from local native plant producers.
Here are some resources that I find to be the most useful:
Plant Selection for Bee Conservation Resources
MSU Native Plant Selection Tool
Michigan Pollinator Initiative: Gardening for Pollinators
Xerces Pollinator Plant Lists
Lady Bird Johnson Wildflower Center Native Bee Plants
Local Plant Producers
Michigan Native Plant Producers Association
Wildtype Native Plant Nursery
Michigan Wildflower Farm
Hidden Savannah Nursery
*Andrena gardineri is a species of miner bees that is a specialist on wildflowers in the genus Packera (shown in photo) while Bombus impatiens is a generalist bee that will visit many wildflower species growing in Michigan. A. gardineri has only been found in Michigan a handful of times.
Gibbs, J., Ascher, J. S., Rightmyer, M. G., & Isaacs, R. (2017). The bees of Michigan (Hymenoptera: Apoidea: Anthophila), with notes on distribution, taxonomy, pollination, and natural history. Zootaxa, 4352(1), 1-160.
Tuell, J. K., Fiedler, A. K., Landis, D., & Isaacs, R. (2008). Visitation by wild and managed bees (Hymenoptera: Apoidea) to eastern U.S. native plants for use in conservation programs. Environmental Entomology, 37(3), 707–718.
M’Gonigle, L. K., Ponisio, L. C., Cutler, K., & Kremen, C. (2015) Habitat restoration promotes pollinator persistence in intensively-managed agriculture. Ecological Applications, 25(6), 1557–1565.
Garbuzov, M., Alton, K., & Ratnieks, F. L. (2017). Most ornamental plants on sale in garden centres are unattractive to flower-visiting insects. PeerJ, 5, e3066.