Bees' ability to withstand heat varies by size and sex

Climate change isn’t just a human problem – it’s affecting the entire planet. One of the biggest concerns is the impact on pollinators, those unsung heroes of the food world. Bees, especially, are facing the brunt of global heat and rising temperatures. But how well can they actually cope?

A team of researchers from Penn State decided to dig into this question, focusing on heat tolerance of a common type of bee – the hoary squash bee.

“Small-bodied, ectothermic — or cold-blooded — insects are considered to be highly vulnerable to changing climate because their ability to maintain proper body temperature depends on external conditions,” said study author Laura Jones, who led the research as a doctoral candidate in ecology at Penn State and is now a postdoctoral fellow at the University of Texas at Austin.

“Understanding how organisms tolerate temperature extremes is critical for assessing the threat climate change poses to species’ distribution and persistence.”

Squash bee size and environment heat

To figure out how squash bees fare in the heat, these scientists had a structured approach. They focused on several key questions:

Impact of Size

Could a bee’s body size directly influence its ability to withstand extreme temperatures? Since male and female squash bees exhibit size differences, the researchers investigated whether this impacted heat tolerance differently between the sexes. They wanted to understand whether larger body size offered any protective benefit against heat stress.

Environmental adaptation

Would bee populations accustomed to hotter climates demonstrate a higher tolerance for rising temperatures? This could offer insights into bees’ potential to adapt over time.

The study aimed to investigate whether long-term exposure to heat within a bee’s environment could lead to increased resilience.

Parasitic threat

Researchers know parasites can generally weaken bees, leading to various health issues. They wanted to examine whether parasitic infections specifically make bees more vulnerable to heat stress, potentially compounding the challenges faced by bees.

This line of inquiry explored the possibility that a compromised immune system due to parasites might leave bees less equipped to handle additional stressors like extreme heat.

Better heat resilience in male squash bees

The relationship between size and heat tolerance in squash bees reveals an unexpected dynamic. While a larger body generally offers some degree of heat resilience for both males and females, the benefit seems particularly pronounced for male bees.

Scientists are still exploring the specific biological mechanisms behind this difference, whether it lies in metabolic differences, surface area to volume ratios, or other physiological factors.

This question opens up an exciting avenue for future research to uncover how size influences heat stress response in these pollinators.

Even more concerning, female squash bees, who shoulder the critical task of foraging and nurturing young, often carry the hidden burden of trypanosome parasites. The study demonstrates that this parasitic infection significantly impairs their ability to cope with extreme temperatures.

This is a major cause for concern. Female bees are essential for hive health and reproduction, and their hindered heat tolerance could have cascading negative effects on the population’s long-term survival and ability to cope with the pressures of climate change.

Heat tolerance of squash bees does not vary by location

The researchers initially hypothesized that squash bee populations in hotter climates would have adaptations for higher temperatures. They expected these bees to evolve traits enhancing thermal tolerance. This expectation is based on the idea that organisms living in extreme environments often develop specialized survival mechanisms over time.

However, the study results contradicted this prediction. Squash bees inhabiting the hottest locations did not show a wider range of heat tolerance compared to those from cooler areas.

This unexpected finding suggests that these particular bees might have reached a physiological limit and are not evolving quickly enough to match the speed of environmental changes.

Even more troubling was the discovery that in the hottest regions, there was less variation in bees’ overall heat tolerance. This finding indicates that extremely high temperatures are effectively eliminating individuals at both ends of the heat tolerance spectrum – those most vulnerable and those most resilient to heat.

The lack of variation means the population is losing genetic diversity related to temperature response, leaving them more susceptible to future heat waves and potentially compromising their long-term survival.

Study implication on heat tolerance of squash bees

This study highlights that heat tolerance in bees is not a simple matter of one or two factors. Instead, an intricate interplay of characteristics like size, sex, parasitic infections, and the specific environmental conditions they experience all contribute to how well they cope with heat stress.

This emphasizes the need for a nuanced approach to understanding the challenges bees face and underscores that solutions might need to be tailored to specific populations.

The findings raise a red flag that bees might struggle to evolve fast enough to outpace the rapid changes brought on by climate change. This suggests that natural adaptation alone might not be sufficient to ensure their survival, underscoring the urgency of human intervention and proactive conservation measures.

This research emphasizes that inaction is not an option. Bees are vital to agriculture and ecosystems. We must actively work towards protecting bee populations by reducing pesticide use, creating pollinator-friendly habitats, and supporting research into bee health.

Individual actions, combined with systemic change, are crucial to safeguarding the future of these indispensable creatures alongside our own.

Bee the change

Here’s how you can make a difference:

Create a pollinator paradise

Transform your yard, balcony, or even a window box into a haven for bees and other pollinators. Plant native wildflowers and flowering herbs that provide a continuous supply of nectar and pollen from early spring through late fall. A diversity of blooms catering to different bee species and preferences is key!

Choose nature-friendly gardening

Pesticides and herbicides are a major contributor to bee decline and have harmful effects on entire ecosystems. Choose organic gardening practices, natural pest control methods, and tolerate some imperfections in your landscape. Your garden isn’t just for you — share it with the creatures that keep our food system thriving.

Igniting awareness

Knowledge is power! Educate yourself about the fascinating world of bees and the threats they face. Share your newfound knowledge with your family, friends, and community.

Encourage others to take bee-friendly actions and create a ripple effect of positive change. Consider supporting organizations dedicated to pollinator conservation and research.

There’s more to be learned, that’s for sure. But science like this helps us understand the challenges bees face and find ways to make our world a safer place for these incredible pollinators. Let’s choose to be part of the solution.

The study is published in the journal Ecology and Evolution.

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