Recent findings provide substantial support for the theory that significant reductions in America’s wild bee populations primarily result from pesticide usage. USC Dornsife scientists assert that preserving these essential pollinators necessitates innovative methods for managing troublesome insects.
Whether you are meandering through a garden, exploring a park, or simply enjoying an open area within the United States, you will likely observe bees flitting around the blossoms. Although honeybees, brought from Europe in the 17th century for honey production, are the most familiar, they are not the sole bees in action. If you possess sharp observational skills, you might catch sight of some of the thousands of less common, indigenous bee species that inhabit these areas.
Indigenous wild bees serve a vital ecological function, promoting the endurance and reproduction of countless plant varieties — including numerous agricultural crops — by disseminating pollen while foraging for sustenance. Regrettably, their populations appear to be dwindling, and despite specialists proposing various reasons, the precise cause remains elusive.
Pesticides and Bee Population Decline
A fresh study published in Nature Sustainability illuminates one possible factor: pesticide application. The investigation uncovers a pronounced decrease in wild bee sightings, with the frequency of certain species plummeting by up to 56% in regions of heightened pesticide use compared to areas with no pesticide application.
The research identifies pesticides as a critical element in the decline of wild bees and suggests that alternative pest management strategies, like those proposed by the U.S. Environmental Protection Agency, could mitigate the harm.
Exploring Declines in Bee Populations
The loss of wild bees could disrupt entire ecosystems, impacting not only plants but also the fauna that rely on those plants for sustenance and habitat. The multibillion-dollar agricultural sector could also be at risk; wild bees, together with honeybees, are vital in pollinating three-fourths of food crops and nearly 90% of flowering plant types.
In response to the pressing threat posed by decreasing bee populations, Laura Melissa Guzman of the USC Dornsife College of Letters, Arts and Sciences, together with an international team of researchers, set out to examine how pesticides impact wild bees. They also investigated the implications of agricultural practices and how the presence of honeybee colonies might affect wild bee communities.
Evaluating Data on Bee Observations
Guzman, Gabilan Assistant Professor of Biological Sciences and Quantitative and Computational Biology, along with the team, scrutinized museum records, ecological surveys, and community science data compiled between 1996 and 2015 from across the contiguous United States.
Utilizing advanced computational techniques, they analyzed over 200,000 distinct observations of more than 1,000 species — encompassing one-third of all known bee species in the U.S. — to evaluate the frequency of various species observed across numerous locales.
Additionally, they examined data from multiple governmental sources, such as the U.S. Geological Survey’s National Land Cover Database and Pesticide National Synthesis Project. The former tracks different land cover types in the U.S. (agricultural, urban, forest, wetland, etc.) with images captured every two to three years from 2001 to 2016, while the latter provides extensive data regarding pesticide usage by county from 1992 to 2021.
By synthesizing these resources, the investigators correlated variables such as land utilization, pesticide application, honeybee colony presence, and types of agricultural crops with wild bee sightings over the preceding two to three decades.
Pesticides: A Key Factor
The investigation presents persuasive evidence that pesticide use is a significant factor contributing to the dwindling wild bee populations. The study uncovered a strong correlation between pesticide application and reduced wild bee sightings, indicating a direct link between pesticide exposure and declines in bee numbers.
Some scientists have theorized that specific crops might negatively impact wild bees. However, Guzman and her colleagues found evidence to refute that claim. Among crops visited by pollinators, they discovered just as many wild bees incounties with significant agriculture compared to those with minimal.
The Unexpected Influence of Honeybee Colonies
Curiously, the research suggested that the existence of honeybee colonies, an introduced species, had virtually no impact on wild bee populations, although some indications may imply otherwise. The researchers do, however, caution that further detailed data and additional investigation are needed to substantiate this finding.
“While our calculations are advanced, much of the spatial and temporal data remains coarse,” Guzman stated. “We intend to enhance our analysis and address the voids as thoroughly as possible.”
Promoting Integrated Pest Management
The researchers consider their results as persuasive evidence that alternative pest control methods, such as integrated pest management, are vital for preserving these essential pollinators.
Integrated pest management encompasses the control of pests utilizing natural predators, altering practices to inhibit pest establishment, and employing traps, barriers, and other physical measures, reserving pesticide usage as a final option.
The team also underscores the importance of conducting longer-term studies that gather data on more localized bee populations over extended timeframes. “We need to merge these extensive studies that cover continents with field investigations that expose bees to chemicals over longer durations and under natural conditions to gain a clearer understanding of how these substances influence bees,” Guzman remarked.
The Necessity for Enhanced Pesticide Risk Assessment
The existing study builds upon research released earlier this year by Guzman and researchers from Washington State University and Canada’s Université Laval. That study indicated that ecological risk assessments (ERAs) underestimate pesticide risks to wild bees and other pollinators.
Currently, ERAs evaluate pesticide impacts on honeybees, frequently through laboratory studies, then apply those conclusions to native bee species. However, Guzman and her colleagues uncovered that existing ERAs can vary drastically — by as much as a million-fold — when determining the lethality of pesticides solely on honeybees. Many wild bee species exhibit even greater sensitivity to pesticides, exacerbating the issue, the study revealed.
“When we solely concentrate on the western honeybee, we overlook the distinctive reactions of other wild bee species to pesticide exposure,” Guzman stated, urging regulatory bodies, researchers, and policymakers to reassess ERA methodologies.
“Increased data and analysis regarding the long-term impacts of pesticides will assist in steering these initiatives for the benefit of all pollinators, including wild bees,” Guzman noted.
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