Rising temperatures overcooked bumblebee food

Bumblebees pollinate many of our favorite foods, but their own diet is being altered by climate change, according to a new study from the University of California, Riverside.

There is an exact point where the flower nectar that bees eat has just the right balance of microbes like bacteria and yeast. Warmer weather can upset that balance, jeopardizing the health of bees and potentially ours.

A study funded by the US National Science Foundation in the journal  Microbial Ecology  examines the effects on an American bumblebee of changes in nectar composition. Without bumblebees, which perform a type of pollination that bees don't, it would be difficult to mass-produce crops like tomatoes, blueberries, bell peppers or potatoes.

"Micro changes in floral nectar can alter the way bumblebees forage and forage, affecting their health and, in turn, potentially affecting human health by reducing the availability of fresh food," said the UC entomologist. Riverside and study leader, Kaleigh Russell.

Bumblebees are attracted to nectar with some microbes, but too much of a good thing can deter them, Russell said.

Even with a small increase in temperature, the microbes' metabolism speeds up, causing them to reproduce more and consume a higher percentage of sugars from the nectar. "Less sugar means the nectar could be less palatable to our pollinators," Russell said.

To test the taste preferences of bumblebees, Russell made nectar in a laboratory. Some were sterile and some contained microbes; grew at lower and higher temperatures.

The lowest temperature, 80.6 degrees Fahrenheit, represents the average spring high for Riverside, California in 2017. The highest temperature, 89.6 F, corresponds to what will be the forecast average temperature at the end of the century due to climate change.

A clear preference for some level of microbes was evident even when the nectar contained less sugar. However, the bees only opted for the less sugary nectar that contains a moderate number of microbes at the coldest temperature. They did not prefer nectar with many microbes or nectar without microbes at all. 

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