When taking a walk in a garden, visiting a park, or enjoying an open area in the United States, you’ll likely see bees busy around the flowers. While honeybees, brought from Europe in the 1600s for honey production, are the most familiar, they’re not the sole bees at work. If you pay close attention, you might catch a glimpse of many native bee species, which are less known but just as important to these environments.
Wild native bees are vital for maintaining ecological balance. They facilitate the reproduction of numerous plant species, including crucial agricultural crops, by transferring pollen while seeking food. Unfortunately, their populations are reportedly decreasing, and although experts suggest various factors, the precise cause remains unclear.
A recent investigation published in Nature Sustainability highlights one possible reason: the use of pesticides. The findings indicate a significant reduction in wild bee sightings, with some species’ appearances plummeting by as much as 56% in regions where pesticides are heavily applied compared to areas free from pesticide application.
This research identifies pesticides as a major contributor to the decline of wild bee populations and recommends exploring alternative pest control techniques, such as those recommended by the U.S. Environmental Protection Agency, as a way to alleviate the damage caused.
Investigating the impact of pesticides on wild bee populations
The decline of wild bees could have cascading effects on entire ecosystems, impacting not just plant life but also the animal species that rely on these plants for survival and habitat. The agricultural sector, worth billions, would also feel the impact; wild bees, together with honeybees, are essential for pollinating around three-quarters of food crops and nearly 90% of flowering plants.
Understanding the serious threat posed by the drop in bee populations, Laura Melissa Guzman from the USC Dornsife College of Letters, Arts and Sciences, along with a team of global researchers, explored how pesticides affect wild bees. They also examined the ramifications of farming practices and the influence of honeybee colonies on wild bee numbers.
Guzman, who is an Assistant Professor of Biological Sciences and Quantitative and Computational Biology, and her colleagues analyzed museum records, ecological surveys, and community science data collected from 1996 to 2015 across the contiguous United States.
Utilizing advanced computational tools, they examined over 200,000 distinct observations of more than 1,000 bee species, which account for one-third of all documented bee species in the U.S., to evaluate how often various species were spotted in different locations.
Furthermore, they scrutinized data from multiple government sources, including the U.S. Geological Survey’s National Land Cover Database, which tracks U.S. land cover types (like crop, urban, forest, wetland, etc.) through periodic snapshots taken from 2001 to 2016, and the Pesticide National Synthesis Project, which details pesticide usage by county from 1992 to 2021.
By combining these datasets, the researchers were able to correlate aspects like land usage, pesticide application, honeybee colony presence, and types of crops with wild bee sightings over the last 20-30 years.
Pesticides recognized as a primary factor affecting wild bees
The study presents compelling evidence that pesticide application significantly contributes to the reduced populations of wild bees. The findings reveal a strong correlation between pesticide usage and lower wild bee sightings, indicating a direct relationship between pesticide exposure and the decline in bee numbers.
While some scientists previously speculated that certain crops could negatively impact wild bee populations, Guzman and her team found evidence contradicting this notion. They discovered comparable wild bee numbers in agricultural-heavy counties versus those with less agriculture.
Interestingly, the research suggested that the presence of honeybee colonies, which are invasive, has minimal impact on wild bee populations, despite some claims to the contrary. The researchers, however, note that further detailed data and studies are needed to solidify this understanding.
“While our calculations are intricate, much of the spatial and temporal data lacks detail,” Guzman explained. “We aim to refine our analysis and address these gaps as thoroughly as possible.”
Wild bees require alternative pest management practices
The findings underscore the necessity for alternative pest control methods, such as integrated pest management, which is crucial for protecting these essential pollinators.
Integrated pest management combines controlling pests through natural predators, altering practices to minimize pest establishment, and using traps, barriers, or other physical means, with the use of pesticides being a last resort.
The researchers also highlight the need for more long-term studies that gather data on local bee populations over extended periods. “We need to merge these continent-spanning large-scale studies with field trials that expose bees to chemicals over longer periods and in natural settings to gain a more accurate understanding of how these substances impact bees,” Guzman asserted.
Making a case for improved pesticide risk evaluation
This study builds upon earlier research conducted by Guzman and scientists from Washington State University and Canada’s Université Laval, finding that ecological risk assessments (ERAs) underestimate the hazards pesticides pose to wild bees and other pollinators.
Currently, ERAs assess pesticide effects on honeybees, typically through laboratory studies, and then apply those results to native bee species. However, Guzman and her team found vast discrepancies in current ERAs—sometimes up to a million-fold—when estimating harm from pesticides on honeybees alone. Moreover, many wild bee species are even more susceptible to pesticides, further complicating the issue, as demonstrated by their findings.
“Focusing solely on the western honeybee overlooks the distinctive responses other wild bee species exhibit when exposed to pesticides,” Guzman remarked, urging regulatory bodies, researchers, and policymakers to rethink ERA methodologies.
“Enhanced data and analysis on the long-term effects of pesticides will help guide these efforts for the benefit of all pollinators, including wild bees,” Guzman emphasized.
Study contributors
Alongside lead author Guzman, the study includes contributions from Elizabeth Elle and Leithen M’Gonigle of Simon Fraser University; Lora Morandin from the Pollinator Partnership; Neil Cobb of the Biodiversity Outreach Network (BON); Paige Chesshire from BON and Northern Arizona University; Lindsie McCabe from the USDA-ARS Pollinating Insects Research Unit; Alice Hughes from the University of Hong Kong; and Michael Orr from the State Museum of Natural History Stuttgart.
