Pollen loads increase heat stress in bumble bees

A recent study conducted by North Carolina State University has shed light on an interesting aspect of bumble bee behavior. It turns out that carrying pollen is quite a workout for these fuzzy creatures, and it significantly raises their body temperature. This newfound understanding of bumble bee body temperatures raises concerns about the potential impact of a warmer world due to climate change on these species.

If you spend some time observing a nearby flower patch, you’re likely to spot a bumble bee with yellow bumps on her back legs. These bumps are actually solid packets of pollen that the bees carefully collect during their foraging trips to transport back to their nests.

Although bees may appear to move effortlessly from one flower to another, these pollen packets can weigh up to a third of their body weight. The study discovered that, after taking into account factors like environmental temperature and body size, the body temperature of bumble bees carrying pollen was significantly higher than that of bees without a load.

The researchers found that for every milligram of pollen carried, the bee’s body temperature increased by 0.07°C. Fully laden bees were found to be 2°C warmer than their unladen counterparts.

Similar to ants and other ectothermic organisms, the body temperature of a bumble bee is predominantly influenced by the environment. Bumble bees are known for their exceptional cold tolerance and will shiver to warm up on chilly days. However, little is known about their ability to tolerate heat.

The fact that pollen-laden bumble bees have higher body temperatures suggests that carrying a full load of pollen on a hot day could expose bees to greater risks, potentially reaching temperatures that are lethal to them.

Malia Naumchik, the lead author of the study and a former applied ecology minor undergraduate, explains, “Getting warmer from carrying pollen could put bumble bees in the range of those stressful, critically hot temperatures. This has important implications for bumble bees and climate change. As environmental temperatures increase, the bees’ operational range of temperatures could shrink significantly.”

Bumble bee populations and species diversity have been declining globally, especially in areas experiencing the effects of climate change. However, the precise mechanisms by which climate change affects bumble bees are not yet fully understood. This recent finding could contribute to unraveling that complex puzzle.

Pollen is crucial at every stage of a bumble bee’s life cycle. Newly emerged queens in the spring need to feed themselves and then nourish their sister workers. These workers, in turn, take charge of feeding the colony, larvae, and future queens. Insufficient pollen, or a lack thereof, can hamper the growth of colonies, jeopardizing future generations and the species as a whole. Additionally, this could have broader implications for pollination and impact agriculture and ecosystems alike.

Elsa Youngsteadt, a professor in applied ecology and the supervisor of Malia’s research, emphasizes the importance of understanding how bumble bees might alter their behavior in response to these findings. “Whether it’s carrying smaller loads of pollen or foraging for shorter durations, it could result in less pollen reaching the colony and fewer plants being pollinated. This is particularly significant since bumble bees play a critical role in ecosystems and are key pollinators for agriculture, especially in the United States and Europe.”

The study titled “Larger pollen loads increase the risk of heat stress in foraging bumblebees” has been published in the journal Biology Letters.

Source: North Carolina State University

Leave a Comment