Researchers in Ohio and the Upper Midwest have delved deep into the world of bumble bees, carrying out a study that observed almost 23,000 bumble bee-flower interactions over a span of two years.
The findings suggest that bumble bees, far from indiscriminate pollen gatherers, display a discerning palate when it comes to the flowers they eat.
Bumble bees, known for their robust size, strength, and sociability, are exceptional long-distance flyers. They play a crucial role in the pollination process, especially in agriculture.
However, they are under threat from various factors, including habitat loss, climate change, and disease. As a result, some species’ numbers are on the decline.
This new information could offer crucial insights for both professional and hobbyist conservationists. It could guide them in making informed planting decisions that support the survival and propagation of these vital pollinators.
“Getting over 20,000 observations of individual identified bumble bees visiting particular flower species is pretty incredible for a dataset,” expressed Karen Goodell, the senior author of the study and a professor of evolution, ecology and organismal biology at The Ohio State University’s Newark campus.
“One of the keys for this project was having flower associations, as well as estimates of flower abundance, so we counted the flowers, too.”
The researchers discovered that the flowers most preferred by bumble bees in Ohio are milkweed, native thistles, morning glory, purple cone flower, bee balm, beardtongue, red clover, vetch and rosinweed, or cup plant. Additionally, two lower abundance species, Culver’s root and wild indigo, proved to be bee magnets.
Published in the journal Ecosphere, the study provides an insight into the eating preferences of 16 historically found bumble bee species in Ohio. The research team was able to observe only 10 species, eight of which were abundant enough to be included in the analysis.
The American bumble bee (Bombus pensylvanicus), a species under consideration for the Federal Endangered Species List, was among them.
The common eastern bumble bee (Bombus impatiens) was the most frequently observed species with 11,555 visits in total. In comparison, only 31 observations were made of the American bumble bee.
However, for the rarer species, the team did not witness enough bee-flower interactions to fully comprehend their diets, highlighting the need for this kind of comprehensive research.
“It’s really important to know what species we do have and what they like to eat, because any of them could become rare,” said Goodell. “The more information we have about their preferences, the better we can manage their habitat.”
During the summer months of 2017 and 2018, the research team conducted fieldwork in 228 locations in Ohio. Their study involved observing bumble bees as they interacted with 96 different species of wildflowers over a total of 477 hours. The observation sites included a range of environments, from unmanaged fields to restored roadsides and meadows, urban patches, and hayfields.
The analysis showed that bumble bee visits to flowers were not random. Bees would often select specific plants more than their availability might suggest.
To measure bees’ flower preferences, researchers used a selection index that compared the frequency of bumble bee species visits to the flowers’ overall percent abundance.
Jessie Lanterman Novotny is the first author of the study and a key player in the project, having contributed as both an Ohio State PhD student and postdoctoral researcher in Goodell’s lab.
“There were flowers that were less abundant that bees actively sought out – they didn’t necessarily eat what was most abundant. There were also plants they avoided: No matter how many of certain flowers there were, they said, ‘No thanks,’” said Lanterman Novotny.
In fact, the researchers were surprised to find that certain plants, though abundant and commonly used in pollinator conservation plantings and seed mixes, were consistently ignored by the bumble bees. These included alsike clover, black-eyed Susan, and prairie cone flower.
A notable finding was that five of the eight observed bumble bee species showed a strong preference for non-native plants. This poses a significant challenge for conservation planters who are focused on preserving native plant species.
Interestingly, the study also revealed that the three most common species did not share the same flower preferences. The researchers found that the floral “menus” of each species overlapped by only one-third or less.
“We compared the flowers each bumble bee species used the most, and species only overlapped by one-third or less,” explained Lanterman Novotny. “Low overlap could relieve competition, so all these species can coexist together.”
The findings highlight the nuanced nature of the relationship between bumble bees and their floral food sources. Bumble bees display complex preferences for certain types of flowers, and these preferences can vary greatly from species to species.
By understanding these preferences, conservationists can make informed decisions to better manage the habitat and diet of these indispensable pollinators.
The research shines a light on the need for continued research into the habits and preferences of bumble bees, particularly as their numbers continue to dwindle due to environmental and man-made challenges.
The study also underscores the crucial role every individual, from professional conservationist to amateur garden enthusiast, can play in ensuring the survival and prosperity of these essential creatures. By planting the right flowers, we can all contribute to the preservation and flourishing of our precious bumble bee populations.
Bees, including honeybees, bumble bees, and solitary bees, are some of the most important pollinators in the world. They contribute significantly to the biodiversity of ecosystems and to the production of food, including fruits, vegetables, nuts, and seeds.
In the agricultural context, pollination is vital for many crops. Bees are often the most efficient pollinators because they actively gather pollen as a food source for their larvae, transferring it from the male parts of a flower to the female parts as they go.
This process fertilizes the flower and allows it to produce fruit and seeds. In fact, it’s estimated that around one-third of the food that we consume each day relies on pollination mainly by bees.
The impact of bees extends beyond agriculture. Many wild plants also depend on bees for pollination, which in turn provides food and habitat for other wildlife. Without bees, these ecosystems could collapse, leading to a decline in biodiversity.
Unfortunately, bees worldwide are facing numerous threats, including from climate change. Changes in temperature, precipitation, and seasonal cues can disrupt the timing of flower blooming and the emergence of bees from their nests.
If bees emerge after flowers have bloomed, they may have less food available, affecting their survival and reproductive rates. Conversely, if flowers bloom after bees have emerged, the flowers may not get pollinated.
Climate change can also shift the geographic ranges of some plants and bees. If the ranges of bees shift differently from the plants they typically pollinate, it could result in a mismatch. This mismatch could reduce the quality of the bees’ diet and the success of plant pollination.
Extreme weather events such as droughts, heatwaves, and heavy rainfall, which are projected to increase with climate change, can also pose significant challenges to bees. For instance, extreme temperatures can be lethal to bees.
Drought can reduce flower availability, depriving bees of their food sources. Excessive rainfall can flood bee nests, especially those of ground-nesting species, killing larvae and forcing adults to abandon their nests.
Lastly, climate change may exacerbate other threats to bees. For example, it could enhance the spread of diseases and parasites or increase the toxicity of pesticides, causing additional stress to bee populations.
Given the critical role bees play in pollination and food production, it’s crucial to mitigate these impacts.
Conservation strategies include creating diverse habitats with a variety of plants that bloom at different times, providing food throughout the season, and promoting sustainable farming practices that reduce pesticide use.
Addressing climate change broadly by reducing greenhouse gas emissions is also key to preserving our invaluable bee populations.