The Short and Imperiled Life of Bees

The lifespan of a bee is just 40 days. This seems short, but during that time it can visit as many as 1,000 blossoms. In so doing, such a short-lived creature can secure the longevity of many a flowering species simply by ferrying pollen from one flower to the next. Multiply that by millions of bees and you have the makings of a diverse ecosystem.

But there are an increasing number of manmade threats can cut a bee’s life even shorter or worse, abort it from the start. The death of one bee might not cause too much concern, but when entire populations are affected along with other pollinators like butterflies, it can have devastating implications for the 87 percent of flowering plants that depend on animal pollination.  

Over the past couple decades, scientists have been uncovering the extent of pollinator decline. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services estimates 40 percent of insect pollinators are at risk of extinction worldwide. In North America, the relative abundance of several bumble bee species has dropped by up to 96 percent.

Several factors are contributing to these declines, including land-use changes, pesticide use, pathogens, competition with managed bees, and climate change. Knowing that time and resources are limited, two scientists recently reviewed all the related research to find which is the most detrimental for pollinators. Not surprisingly, it’s the factor that is the hardest to stop: climate change.

In mid-May, the journal Commonwealth Agricultural Bureau International Reviews published the findings of Wisconsin researcher Johanne Brunet, who had scoured more than 150 journal articles related to worldwide pollinator decline. She concluded that to save pollinators, a more holistic approach is needed, one where natural habitat is integrated with agricultural lands that are treated with less pesticide. But because climate change poses the greatest threat to pollinators, nations across the globe must do more to reduce greenhouse gases.

“Climate change has the most diverse negative impacts on pollinators and is the threat most difficult to control,” Brunet said in a May 15 release. “However, its consequences threaten food security and world stability, thus efforts to control it must be prioritized at a global scale.”

In the realm of research, insects have often been overlooked unless a specific bug jeopardizes a valuable crop, such as the mountain pine beetle which threatens various timber species. Plus, insects can be difficult to study since many are hard to find and sampling methods can be lethal. Over the past few decades, however, issues such as honeybee colony collapse have prompted scientists to start investigating the 20,000 bee species that exist worldwide, 85 percent of which live solitary lives instead of clustering in hives.

Researchers studied how pollinators would react in general to overall climate trends using models that predict increasing worldwide average temperatures and drought in some areas, and higher rainfall in others. The changes in water and temperature are predicted to affect plants and their pollinators, particularly in specialized systems where one species depends primarily on another, such as milkweed and monarch butterflies.

Drought and higher temperatures caused by a warming climate, for example, can decrease the size or the number of flowers a plant produces and can even change a flower’s scent. These alterations could make it more difficult for pollinators to locate flowers. Also, drought or heat would tend to cause the few small blossoms that remain to produce less nectar and pollen, so a bee or butterfly would receive less of a reward. Both trends need further research to determine any effect on pollinators, Brunet said.

Scientists have also predicted that higher temperatures can alter the time of year when pollinators emerge and when plants begin to flower. That could cause problems if pollinators appear before flowers begin to bloom or vice versa, but so far that scenario not been documented.

Colorado State University graduate student Kathleen Whipple tried to find such a disconnect in the pollinators and flowers of Yellowstone National Park. She chose the park for her study site partly because it’s free from most other threats to pollinators, so any observed shift could be credited to climate change. It also meant she could take advantage of several decades of data that her advisor, Gillian Bowser, has gathered in the park.

In the 1980s, when Bowser was searching for a graduate project, National Park Service biologist Mary Meagher suggested that Bowser investigate Yellowstone’s pollinators, most if not all of which were unknown at the time. Taking the advice, Bowser researched butterflies and plants in the Cougar Creek area of the park and has repeatedly returned to document 400 species of butterflies.

With each successive visit, Bowser and Whipple have seen changes in Cougar Creek, including faster snowmelt and earlier flower blooms. Whipple noted in her 2023 dissertation that flowers are now blooming on average three days earlier than in the 1980s, but that shift is still too small to see any resulting divergence between flower availability and pollinator visits.

While Yellowstone provides an almost unsullied ecosystem for such study, it has one aspect that can obscure the effects of climate change: its mountains and the elevational gradient they offer. For example, while the mid-elevation Cougar Creek meadow has seen a three-day shift in flower onset, the shift in the subalpine plants occurs five days earlier at higher elevations where warming has a greater effect. But pollinators can fly up or down to wherever flowers might be blooming, so any lack of synchrony is blurred.

Whipple concluded, “the climate in the GYE has changed, but pollinator and floral species responses to such change are less clear.” Again, she said, more research is needed.

“Understanding these shifts is so important for us to protect pollinators in the long run because they’re little, tiny guys. They’re hard to see sometimes, but they perform such a critical service for us in terms of our food crops and agricultural systems as well as the preservation of our national parks, yet we pay very little attention to what’s happening to them regarding climate change,” Bowser said in a CSU release.

However, the direct effect of heat on pollinators is very clear and very scary. Brunet’s review shows that larval and adult insects, like most animals, are more likely to die in high heat. Either that or they move away, escaping to higher elevations or farther north, causing localized extinction. That’s particularly devastating in those specialized systems where a plant species could be left without its pollinator. That plant dies out too.

Last year, the U.S. Fish and Wildlife Service published a study that found increasing temperature, particularly the extended heat waves that have increasingly settled over the Northern Rocky Mountains, have a devastating effect on larger bees, including the western bumble bee, which is most abundant in Greater Yellowstone but has seen a 57 percent decline in its historical range, according to the study.

“Even considering the most optimistic scenario, western bumble bee populations are expected to continue to decline in the near future in nearly half of the regions across the bumble bee’s range,” said USGS scientist Tabitha Graves said in a January 2023 release. “Considering the more severe, but probably more likely scenarios, western bumble bee populations are expected to decline an additional 51 percent to 97 percent from 2020 levels depending on the region.” 

The western bumble bee is one of several bumble bees being considered for endangered species listing due to climate change effects, but also the use of pesticides, especially neonicotinoids, which attack insect nervous systems. Western bumble bees have been documented visiting huckleberry, snowberry and penstemon flowers among others, so their extinction could noticeably change the vegetation of the West.

For most threats that pollinators face, Brunet identified several solutions. When it comes to pesticides and other chemicals, people can reduce their effect by using fewer toxic chemicals and spraying at night when pollinators aren’t active. Human development of wild lands poses a major threat because it eliminates food sources and nesting spots, and forces pollinators to fly greater distances to find flowers as habitat becomes more fragmented. In these developed areas, people can improve conditions by planting native flower gardens and by maintaining wild habitat around agricultural fields, Brunet said.

But when it comes to the changing climate, no immediate solutions exist to help pollinators. That’s all the more reason to eliminate what threats we can.

“Climate change is the most critical threat to pollinators, and research must continue to study its impacts and develop solutions,” Brunet concluded in the review. “Public education on the negative impacts of climate change on plants and their pollinators and the implications for human diet and lives must take place at a global scale. Climate change is a global problem and a political one with strong implications for food security and world stability.”

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