Carrying pollen causes bumble bees to overheat, raising fresh concerns about climate change.

Bumble bees’ body temperature significantly rises when they carry pollen, according to a new study from North Carolina State University. Questions about how these species will be affected by a warmer world as a result of climate change arise as a result of this new understanding of active bumble bee body temperatures.

A fuzzy bumble bee with yellow bumps on her back legs can be found if you spend some time at a nearby flower patch. During the bees’ foraging journey, these yellow bumps are solid packets of pollen that have been carefully collected and transported back to their nests.

These pollen packets can weigh up to a third of a bee’s body weight, despite the bees’ apparent ease of movement from flower to flower. That’s what this new investigation discovered: subsequent to representing natural temperature and body size, the internal heat level of honey bees conveying dust was altogether more sweltering than the temperature of honey bees that were unfilled-legged.

“Being warmer as a result of pollen transport could put bumble bees in the range of those stressful, critically hot temperatures. This has serious consequences for bumble bees and climate change. As external temperatures rise, the operational temperature range of bees may narrow dramatically.”

Malia Naumchik, a former applied ecology minor undergraduate and lead author of the study.

The researchers found that fully laden bees were 2°C warmer than unladen bees, with body temperatures rising by 0.07°C for every milligram of pollen they carried.

Like subterranean insects and different ectotherms, the internal heat level of a honey bee is still affected by the climate. Among honey bees, honey bees are particularly cold-minded and will shudder to heat up during cold days. However, little is known about their heat tolerance.

It’s possible that carrying a full load of pollen on a hot day puts bees at greater risk of reaching the temperature threshold that could kill them because pollen-laden bumble bees are hotter than unladen bees.

Malia Naumchik, the study’s lead author and a former applied ecology minor, says, “Getting warmer from carrying pollen could put bumble bees in the range of those stressful, critically hot temperatures.” The impact on bumble bees and climate change is significantd ecology minor, says, “Getting warmer from carrying pollen could put bumble bees in the range of those stressful, critically hot temperatures.” The impact on bumble bees and climate change is significant. The bees’ operating temperature range may significantly decrease as environmental temperatures rise.”

Worldwide, the number of bumble bee species and their diversity are decreasing, particularly in regions that are warming up as a result of climate change. However, the precise mechanisms by which climate change affects bumble bees are still poorly understood. This discovery may be a component of that puzzle.

Every stage of a bumble bee’s life cycle depends on pollen. In the spring, newly emerged queens need to eat first for themselves and then for their sister workers. The colony, larvae, and future queens are then fed by those workers. Colonies will not thrive without pollen or in sufficient quantities, putting future colonies and the species at risk. This could have an effect on agriculture and ecosystems, as well as pollination in general.

“We want to realize how honey bees might change their way of behaving to more readily comprehend what this could mean for how much dust they gather and how much fertilization they perform during hot days,” says Elsa Youngsteadt, a teacher in applied environment and manager of Malia’s examination.

“It could result in less pollen reaching the colony and fewer plants being pollinated, regardless of whether it is carrying smaller loads of pollen or foraging for shorter periods of time. This is especially significant because bumble bees are essential pollinators for agriculture and provide essential ecosystem services, particularly in the United States and Europe.

In the journal Biology Letters, a paper titled “Larger pollen loads increase the risk of heat stress in foraging bumblebees” was published.

More information: Malia Naumchik et al, Larger pollen loads increase risk of heat stress in foraging bumblebees, Biology Letters (2023). DOI: 10.1098/ … .1098/rsbl.2022.0581

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