Rising temperatures overcook bumblebees' brunch

This nectar preference experiment used Bombus impatiens, also known as the common eastern bee or the common eastern bumblebee to taste the nectar. Credit: Brooke Alexander
According to a new UC Riverside research, although bees pollinate many of our favourite foods, their diet is being disrupted by climate change.

There is a sweet spot in which floral nectar bees consume has the right amount of microbes such as yeast and bacteria. Hotter weather can disrupt the balance, posing a risk to the bees' and our health.

The effects of nectar composition changes on an American Bumblebee are the subject of a new study published in Microbial Ecology. It would be impossible to produce large quantities of food crops such as tomatoes, blueberries and peppers without bumblebees. They perform a different type of pollination than honeybees.

Kaleigh Russell, UCR entomologist, and study leader, said that micro changes in floral nectar could alter bees' foraging and food search patterns, which in turn may affect their health.

Russell stated that although bees enjoy nectar with microbes, too much can discourage them.

Microbes can reproduce faster if there is a slight increase in temperature. Russell stated that nectar with less sugar could be less appealing to pollinators.

Russell created nectar in a laboratory to test the taste buds of the bumblebees. She grew some at a lower temperature and some at a higher one.

Riverside's average springtime temperature in 2017 was 80.6 degrees Fahrenheit. The temperature of 89.6 F corresponds to what the average temperature will be by the end century because of climate change.

Even though the nectar had less sugar, there was a clear preference for microbes. The bees preferred the nectar with a lower sugar content and a higher level of microbes at a cooler temperature. They didn't prefer nectar with too much microbes or none at all.

It's not yet known why bees have specific preferences. Russell suggests that bees may benefit from yeast or bacteria digesting sugars in nectar. Another possibility is that microbes may produce secondary metabolites to aid bee health.

It is unlikely that an increase of average temperatures will have any positive effects on bumblebees.

Russell stated that there could be shifts in the location of bee colonies, as they will leave when they don't have the food they need. "We could also see a decrease in overall pollinator population."

Russell suggests that gardeners who are concerned about their gardens grow native plants that haven't been treated with insecticides. She said, "That's probably the best thing anyone could do right now in order to help bumblebees."

Continue reading Yeasts in nectar may stimulate the growth bee colonies

Further information: Kaleigh Russell et. al., Elevated temperature may affect nectar microbes, nectar sugars and bee foraging preferences, Microbial Ecology (2021). Kaleigh A. Russell and colleagues, Elevated temperature may affect Nectar microbes, Nectar sugars, and Bumble be foraging preference, (2021). DOI: 10.1007/s00248-021-01881-x