Reorganizing Pest Control to Save Our Bees

New research provides strong evidence to support suspicions that the dramatic decline in wild bee populations in America is largely due to pesticide use. University of Southern California Dornsife scientists say that to save essential pollinators, new approaches are needed to manage insect pests.

Whether you’re strolling through a garden, walking in a park, or simply enjoying an open space in the United States, you’re likely to notice bees buzzing around flowers. While honeybees, imported from Europe in the 17th century to produce honey, are the most recognizable, they’re not the only bees at work. If you’re a keen observer, you might spot some of the thousands of less familiar native bees. species who consider these spaces as their home.

Native wild bees play a crucial ecological role, ensuring the survival and reproduction of countless plant species, including many agricultural crops, by spreading pollen as they search for food. Unfortunately, their numbers appear to be declining, and while experts suggest multiple causes, the exact reason remains a mystery.

Pesticides and bee decline

A new study published in Nature and sustainability The study highlights a potential cause: pesticide use. The study found a sharp decline in the number of wild bee sightings, with some species seeing a 56% decrease in areas where pesticide use is high compared to areas where it is zero.

The study points to pesticides as a major factor in the decline of wild bees and suggests that alternative pest control methods, such as those proposed by the U.S. Environmental Protection Agency, could reduce the damage.

Investigation into the decline of bee populations

The loss of wild bees could disrupt entire ecosystems, affecting not only plants but also the wildlife that depends on those plants for food and livelihoods. The multi-billion dollar agricultural industry could also suffer: wild bees, along with honeybees, play a crucial role in pollinating three-quarters of food crops and nearly 90% of flowering plant species.

Recognizing the urgent threat of declining bee populations, Laura Melissa Guzman of the USC Dornsife College of Letters, Arts and Sciences and an international team of researchers set out to study the impact of pesticides on wild bees. They also studied the effects of agricultural practices and how the presence of honeybee colonies might influence wild bee populations.

Analysis of data on bee observations

Guzman, an assistant professor of biological sciences and quantitative and computational biology at Gabilan, and his team inspected museum archives, ecological surveys and community science data collected between 1996 and 2015 across the contiguous United States.

Using advanced computational methods, they sifted through more than 200,000 unique observations of more than 1,000 species – representing a third of all known bee species in the United States – to assess how often different species were observed in different locations.

In addition, they analyzed data from several government sources, such as the U.S. Geological Survey’s National Land Cover Database and the Pesticide National Synthesis Project. The former tracks U.S. land cover types (crops, urban areas, forests, wetlands, etc.) with snapshots taken every two to three years from 2001 to 2016, while the latter provides detailed data on pesticide use by county from 1992 to 2021.

By integrating these resources, the researchers correlated factors such as land use, pesticide application, presence of bee colonies and types of agricultural crops with observations of wild bees over the past two to three decades.

Pesticides: a major culprit

The study provides compelling evidence that pesticide use is a major contributor to the decline in wild bee numbers. The study found a strong correlation between pesticide use and observed declines in wild bee numbers, suggesting a direct link between pesticide exposure and bee population declines.

Some scientists have speculated that certain crops might have a negative effect on wild bees. However, Guzman and his team found evidence to the contrary. Among crops frequented by pollinators, they found as many wild bees in counties with high levels of agriculture as in counties with low levels of agriculture.

The surprising impact of bee colonies

Interestingly, the study suggested that the presence of honeybee colonies, an invasive species, had virtually no effect on wild bee populations, despite some evidence to the contrary. The researchers caution, however, that they need more detailed data and further studies to confirm this conclusion.

“Although our calculations are sophisticated, much of the spatial and temporal data is coarse,” Guzman said. “We plan to refine our analysis and fill in the gaps as much as possible.”

Advocacy for integrated pest management

The researchers see their findings as compelling evidence that alternative pest management strategies, such as integrated pest management, are essential to conserve these essential pollinators.

Integrated pest management involves controlling pests by using natural predators, modifying practices to reduce pest establishment, and using traps, barriers, and other physical means, with the use of pesticides being reserved as a last resort.

The team also emphasizes the need for longer-term studies that collect data on more localized bee populations over extended periods of time. “We need to combine these large-scale studies that span multiple continents with field experiments that expose bees to chemicals over longer periods of time and in natural conditions to get a clearer picture of how these chemicals affect bees,” Guzman said.

The need for better risk assessment of pesticides

The current study builds on work published earlier this year by Guzman and scientists at Washington State University and Laval University in Canada. That study found that ecological risk assessments (ERAs) underestimate the threats that pesticides pose to wild bees and other pollinators.

Currently, ERAs measure the effects of pesticides on bees, often in laboratory studies, and then extrapolate those results to native bee species. However, Guzman and his colleagues found that current ERAs vary wildly—up to a million-fold—when it comes to estimating the degree of pesticide mortality for bees alone. And many wild bees are even more susceptible to pesticides, compounding the problem, the research suggests.

“When we focus only on the western honeybee, we ignore the unique responses of other wild bee species to pesticide exposure,” Guzman said, calling on regulatory agencies, scientists and policymakers to rethink ERA methods.

“More data and analysis on the long-term effects of pesticides will help guide these efforts to benefit all pollinators, including wild bees,” Guzman said.

Reference: “Impact of Pesticide Use on the Distribution of Wild Bees in the United States” August 27, 2024, Nature and sustainability.
DOI: 10.1038/s41893-024-01413-8

In addition to corresponding author Guzman, the study’s authors include Elizabeth Elle and Leithen M’Gonigle of Simon Fraser University; Lora Morandin of the Pollinator Partnership; Neil Cobb of the Biodiversity Outreach Network (BON); Paige Chesshire of BON and Northern Arizona University; Lindsie McCabe of the USDA-ARS Pollinator Research Unit; Alice Hughes of the University of Hong Kong; and Michael Orr of the Natural History Museum Stuttgart.

Funding: US National Science Foundation, USC Dornsife, Simon Fraser University, Natural Sciences and Engineering Research Council of Canada, Liber Ero Fellowship Program