As I get close to finishing my dissertation, I am reflecting on the way that the PAm-Costco Scholar Fellowship has helped me to take my interest in honey bee foraging behavior and apply it to helping beekeepers and land managers who want to support honey bees.
I started studying bees a few years after increased colony mortality had drawn international public attention and concern. Research since that time has highlighted four major stressors that contribute to high mortality: parasites, pathogens, pesticides, and poor nutrition. Good nutrition is not only essential to day-to-day activities of bees, but it also helps colonies deal with the other stressors. Finding apiary spots that lead to good colony nutrition is challenging because honey bee colonies have a very wide foraging range, in some cases traveling over 8 miles to collect food. If we consider that most foraging happens within 2 miles of a hive, that’s still over 8,000 acres that foragers are covering to find rewarding flowers.
When I started working in Marla Spivak’s lab at the University of Minnesota I quickly learned that states in the Upper Midwest region are some of the top honey-producing states in the country, and a large proportion of colonies that travel to pollinate crops spend their summers here. However, the Upper Midwest is also an area where landscapes have changed dramatically. Historically, this region was mostly covered by prairie, but since that time almost all of the original prairie lands have been converted to agriculture, today mainly corn and soybeans. We also have a number of non-native weedy plants brought to North America as forage crops for cattle that have now become the dominant roadside forb species. Recent efforts to restore/reconstruct prairie habitats to conserve native biodiversity have led beekeepers to wonder whether honey bees will collect large amounts of food from nearby prairies. It has also led to questions from land managers interested in planting native flowers about which native prairie species might make good replacements for non-native roadside flowers that would still attract and benefit honey bees.
I started my dissertation with some experience studying honey bee foraging. However, my previous research was focused on questions about how honey bees communicate and divide up labor, not on practical questions about how colonies assess the flowers in the landscapes around them. Through my dissertation work I learned a great deal about how floral resources change throughout the season in the Upper Midwest and which species beekeepers generally consider the best honey plants here. I also learned many techniques for studying honey bee foraging preferences, including how to identify bee-collected pollen grains, both under the microscope and by sequencing their DNA, and how to decode and map waggle dance communications between honey bee foragers about the locations of the most profitable patches of flowers.
With support from the PAm-Costco Scholar Fellowship, we asked the question: when given access to restored prairies, what proportion of their diet will honey bee colonies collect from prairie flowers? To answer this question, we placed colonies near four large, restored prairies and examined the pollen coming into those colonies throughout the foraging season. We found little contribution from native prairie species until July and the highest contribution of native species in August and September, when native aster species, such as goldenrods, became a major source of food. From June to September, our colonies collected large proportions of their pollen from three non-native genera: white/alsike/red clovers, sweet clovers, and birds-foot trefoil.
The honey bee foraging strategy involves communications among foragers about the locations (distance/direction) of the most profitable patches of flowers. Therefore, to understand colony foraging decisions we asked: to what extent do honey bee foragers advertise flower patches in prairies? To determine more precisely where our bees found their preferred flowers, we placed glass-walled observation hives near two large prairies and decoded/mapped waggle dance communications between foragers in those hives.
Maps of the dance decoding results showed that most flower patches advertised by foragers were outside of the restored prairies, but at one site we saw increasing use of prairie flower patches in the late summer and early fall1. We also found that our honey bees advertised seven types of native prairie flowers as profitable pollen sources: goldenrods, purple prairie clover, giant hyssops, white prairie clover, ragweed, partridge pea, and something in the sunflower tribe (probably a coneflower species)1. Including a higher proportion of prairie clover and giant hyssop in bee-friendly seed mixes may make prairies more attractive resources for honey bees in July when colonies generally produce the most honey.
These seasonal patterns raise the question: what makes prairies more attractive at certain times of year? How do factors such as species, floral density, and floral diversity affect honey bees’ evaluations of flowers in prairies and thus colony-level foraging behavior? We are now analyzing data from an experiment testing the effects of flower density on honey bee recruitment. Future studies could also test the effects of species composition and floral diversity and help us determine how to design native plantings to maximize their attractiveness to honey bee colonies.
Costco and Project Apis m.’s generous support has extended to supporting another on-going experiment called the Minnesota Agriculture for Pollinators Project. That project is looking at the effect of bee-friendly plantings and landscape composition on wild bees and honey bee colonies. We are currently working with Dr. Dan Cariveau to identify the pollens collected by honey bee colonies at sites that varied in the percentage of agriculture in the surrounding landscape and the size of bee-friendly plantings designed by the Bee and Butterfly Habitat Fund. This study will help us better understand the effects of bee-friendly plantings in different landscapes on honey bee foraging choices, colony diet protein/lipid composition, and colony health. I look forward to continuing to study honey bee foraging behavior and applying what I learn to help beekeepers keep their colonies well-nourished.
1. Carr-Markell MK, Demler CM, Couvillon MJ, Schürch R, Spivak M. Do honey bee (Apis mellifera) foragers recruit their nestmates to native forbs in reconstructed prairie habitats? PLOS ONE. 2020; https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0228169