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July, 2020

Bringing back the buzz to America’s back yards

by Matthew Beattie

For the last three decades, native wild bee populations have been vanishing from the landscapes of North America at an alarming rate. However, few species have declined more rapidly than the once-common rusty patched bumble bee. Today, conservation groups like the Xerces Society are working valiantly to stop them from disappearing altogether

In the middle of the 1990s, late and sadly missed Emeritus Professor Robbin Thorp, a leading entomologist at University of California, Davis, was conducting a long-term study of native bee populations in Oregon and Northern California, when he noticed that something was amiss. Upon revisiting survey sites, he was finding that certain species he had recorded in previous years were disappearing – or had vanished altogether. This was not just limited to single localities, but across his study region. Deeply concerned by his findings, he flagged the mystery to other insect experts across North America. More surveys soon followed elsewhere, and they confirmed his worst fears: America’s native bee species were disappearing from locations across the continent at an alarming rate. 

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Xerces Society for Invertebrate Conservation bumble bee specialist and biologist Rich Hatfield searches for rusty patched bumble bees in a patch of Joe-Pye weed at the
University of Wisconsin Arboretum, Madison, Wisconsin, USA.

A species under pressure

One species seemed to be under especially severe pressure. The rusty patched bumble bee was once a common sight from the Dakotas, across the Midwest to Maine, and populations had historically extended as far south as Georgia. Today, numbers are around ten percent of what they once were, and the species has disappeared altogether from many areas. Bee populations are falling worldwide, but the fall in rusty patched bumble bee numbers is remarkable both in the scale and speed at which it has happened. 

Distinctive markings

Rusty patched bumble bees – or at least the males and the workers – can be distinguished from other native North American bumble bee species by a rust colored patch on their backs, surrounded by yellow hairs (queens do not have the marking, and they are seldom seen in the open as they remain in the nest laying eggs). It is this rust coloring that gives the species its distinctive name, although the scientific community tends to know it by its Latin name Bombus affinis: “The rusty patched bumble bee is a very early emerging species and very late to senesce [age],” says Rich Hatfield, Senior Conservation Biologist with the Xerces Society, an international non-profit organizationdedicated to the study and conservation of invertebrates. “Therefore, it has a long lifecycle. Colony sizes can be very large: a nest with over 500 individuals over the course of a season was probably once possible.” Nowadays, with  populations in such steep decline, it is difficult to know whether such large colonies still exist: “One of the challenges of studying the rusty patched bumble bee right now is that they are so rare,” Hatfield explains. 

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A recipe for population decline

Rather than one single reason for the decline of the rusty patched bumble bee and other US native bee species, there are several and they all add up to a perfect storm: “One major factor is pesticides,” Hatfield says. “The systemic use of neonicotinoid insecticides began in the 1990s, at around the same time as the decline in bee populations. Habitat loss is another significant issue: as our cities grow and we increase agricultural production, we are gobbling up habitat.” In addition to these, Hatfield states that the twin challenges of invasive foreign plant species and climate change are putting pressure on sources of food for bees by changing ecosystems and altering flowering patterns. “But significantly for the rusty patched bumble bee, yet another factor on top of these seems to be disease: in this case a fungal  athogen called Nosema bombi, which evidence suggests the rusty patch may be particularly susceptible to.” 

Pollinators in transit

There is a correlation between the rapid spread of Nosema bombi across North America, and the growth of the commercial bumble bee industry, which began in the 1990s. “People learned how to breed bumble bees in boxes and ship them to greenhouses, mostly for tomato pollination,” Hatfield explains. “Evidence suggests that as this industry expanded and grew in importance for the agricultural sector, the transportation of those commercial bumble bees helped to amplify the spread of Nosema bombi across the country. Commercial bees likely didn’t introduce the pathogen, but they helped it spread much more rapidly and in higher concentrations than it would have on its own.” 

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A central bumble bee pollinates wildflowers in the Bridger Range, Bozeman, Montana.

Changing attitudes and raising awareness

As part of his role with the Xerces Society, Rich Hatfield is responsible for leading the organization’s bumble bee program, which aims to address the decline of America’s threatened native bumble bee species – including the rusty patched bumble bee – through research, conservation, advocacy and education. “We started working on the rusty patched bumble bee in the late 2000s,” he says. “Our goal was really to start collecting  observations of these animals and trying to figure out where they were living. The first step in any conservation effort for a species of concern is to find out whereabouts they are and what’s important to them.” 

Community science

By learning more about the ecosystems where bee populations are still thriving, researchers can make recommendations for landowners to improve the areas where they are not. “Collecting that baseline information is an ongoing project for us and we have a few different ways that we’re doing that. One is through a community science project called Bumble Bee Watch, where we’re encouraging people to take photographs with their cameras or smartphones and submit them to help us document bumble bee populations across North America.”

A hive of research activity

The response to Bumble Bee Watch has been huge, with around 15,000 users registered across the United States and Canada and nearly 45,000 submitted Becky Nichols, an entomologist with the National Park Service who is based in Great Smoky Mountains National Park, Tennessee with specimens of rusty patched bumble bees found in the park. sightings logged to the  database. The data generated has given researchers a population density map of bee populations in the areas where people live; however, it has been less useful for gathering data from the vast tracts of land in North America that are still wilderness. In these places, the Xerces Society is conducting atlas projects – systematic research across predefined areas of land – to gather data  about remote bee populations.There are currently two such projects ongoing: one in the Pacific Northwest and another in Nebraska. “We’re gathering data so we can make evidence-based recommendations to large land managers like the US Forest Service, to help them with restoration projects that put habitat back on the ground for the bees.” 

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Becky Nichols, an entomologist with the National Park Service who is based in Great Smoky Mountains National Park, Tennessee with specimens of rusty patched bumble bees found in the park.

Hope for a brighter future

It is still early days as to whether conservation efforts are having a positive impact on rusty patched bumble bee populations. Several more years of research are needed before there is sufficient data to indicate any improvement, but there are some encouraging signs that the tireless efforts of the Xerces Society are making a wider difference to people’s understanding of how important bees are to all of us. “We have a whole team that  works with farmers to help them create habitats that are beneficial for native pollinators. This helps them to benefit from the pollination services of native bees and reduces their dependency on (non-native) European honey bees. Over the last 15 years or so, this has led to the improvement of around 750,000 acres of pollinator habitat across North America.”

“We’re gathering data so we can make evidence-­based recommendations to large land managers like the US Forest Service, to help them with ­restoration projects that put habitat back on the ground for the bees. ” Rich Hatfield, Senior Conservation Biologist at Xerces Society

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