Western Bumblebee Populations Collapsing: Short on Data

Western bumblebee populations have declined by 93% over the last two decades. Find out how researchers support action to conserve these vital pollinators.

As I’ve written before in these pages, one of the earliest toys I remember playing with was a tiny ceramic bumblebee at my grandmother’s house. There was something charismatic about this little character, and my brothers and I are still sentimental about him.

We called him Buzzy Bee, and although he’s had to be glued together after numerous mishaps, he’s still smiling and still in the family. He’s passed from my grandmother through three generations to my grandnephew as a keepsake.

We humans have an ambivalent relationship with bees, and bumblebees in particular. 

They can deliver a nasty sting, but they only use it as a last resort.

Bumblebees Are Endearing in their Appearance

Otherwise, bumblebees are endearing in their appearance. We also know that they pollinate our gardens and flowers.

As readers will have heard, bee populations are declining worldwide. The reasons for this are still a mystery to science. As with most aspects of conservation, there are multiple reasons for this, but they all boil down to human activity.

According to the UN Food and Agriculture Organization (FAO), bees now face extinction rates between 100 and 1,000 times higher than usual. About 35% of our bees and butterflies are close to extinction worldwide.

Extinction Rates 100 to 1,000 Times Higher than Usual

This is critical because 95% of our flowering species, 75% of our crops and 35% of our farmland rely on animal pollination. As our world population climbs toward ten billion, we can’t meet the challenge of feeding everybody without our hardworking bee population.

The journal Ecosphere published a study this week that delves into the decline in the western bumblebee (bombis occidentalis), a medium-sized bee with the familiar black and yellow hair. The paper results from three years of teamwork with leading experts by Professor Lusha Tronstad and Ph.D. candidate Christy Bell at the University of Wyoming.

Professor Tronstad is part of the Wyoming Natural Diversity Database (WYNDD). She has concluded that “The decline of the Western bumble bee is likely not limited to one culprit but, instead, due to several factors that interact such as pesticides, pathogens, climate change and habitat loss.” 

ODDS of Spotting a Western Bumblebee Fell by 93%

The study results came from collaboration within the Western Bumblebee Working Group, of which both co-authors are active members. Using a sophisticated statistical sampling technique called occupancy modelling, the researchers found that the odds of spotting a western bumblebee fell by 93% between 1998 and 2018.

The paper reviews what we know about the western bumblebee. Perhaps more importantly, what we still don’t know. Researchers are hindered by data gaps in regions like Alaska, Northwestern Canada and parts of the US Southwest.

The goal of the study is to provide information to the US Fish and Wildlife Service. They will use the data to decide whether to classify the western bumblebee as an endangered species.

“Data on which Management Decisions Can Be Based”

Professor Tronstad explains, “At WYNDD, we collect data, and that data is used by managers. Our mission is to provide the most up-to-date data on which management decisions can be based.”

By going through 156 research papers on the topic, the team came up with a list of the things that are stressing the western bumblebee. These include, “pathogens, pesticides, habitat loss and degradation, climate change, livestock grazing, competition from non‐native bees, and synergistic effects of these stressors.”

The trouble is that the gaps in the data mentioned above make it hard to work out which of these stressors pose the most significant problems. It’s also hard to determine how these disruptions interact with each other in the wild.

Pathogens, Pesticides, Climate Change and Habitat Loss

Even so, the researchers identified four threats that they believe are the most significant concerns. These are pathogens, pesticides, climate change, and habitat loss.

The team calls for these four areas to be priorities for further research. Readers will notice that each of these four hazards result from human activity.

The team keeps emphasizing the lack of useful data because the range of the western bumblebee is enormous. Any steps authorities take to address their decline in numbers will be costly and complicated.

Range of Western Bumblebee is Enormous

That makes it essential to provide those authorities with complete and accurate data to support their decision making. Otherwise, time and resources could be wasted, leaving the bumblebees, and us, no better off in the long run.

Even so, we don’t have to wait for the conservation experts to reach a consensus. Professor Tronstad pointed to three things everyone can do to support pollinators in their local habitat.

These are:

·      Plant flowers that bloom all summer long. Make sure that you plant varieties that rely on pollen, and that produce lots of nectar to attract the bees.

·      Provide a water source for the bees. Add a piece of wood or some other type of ledge so that they can get to the water without falling in.

·      Provide nest sites and overwintering habitat. Bumblebees nest underground, so leaving a few bare patches with some ground cover will give them a place to shelter.

“Once the Most Abundant Bumblebees on the West Coast”

Professor Lusha concluded by saying, “Western bumblebees were once the most abundant bumblebees on the West Coast of the US, but they are much less frequently observed there now. Pathogens (or parasites) are thought to be a major reason for their decline.”

The threats to the western bumblebee remind us that everything in nature is connected. These tiny insects usually go unnoticed, yet because of their interactions with other species, losing them is like making the wrong pull from a house of cards.

Christy Bell will be out in the field again this summer. She and two assistants will be investigating the pathogens that affect western bumblebee populations in Wyoming’s Rocky Mountains.

We always have more to learn if we dare to know.
Learn more:
We all depend on the survival of bees
UW Researchers Look for Answers as to Why Western Bumblebees Are Declining
Western bumble bee: declines in the continental United States and range‐wide information gaps
Mass Extinction Happening Again
Bee Pollination, Habitats and Human Meddling
Biodiversity Always Wins


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