05
Dec
Sublethal Pesticide Exposure, Inadequately Regulated, Adversely Affects Insect Health, Study Finds
(Beyond Pesticides, December 5, 2024) A novel, comprehensive study published in Science reviews a library of 1,024 different chemicals (herbicides, insecticides, fungicides, and plant inhibitors) finding that, even at “sublethal” exposure levels, 57% of tested chemicals impact the behavioral and physiological health of house fly larvae. Mosquito and butterfly populations are also susceptible to long-term adverse effects at sublethal levels.
Environmental and public health advocates continue to raise concerns about adverse effects resulting from the failure of the U.S. Environmental Protection Agency (EPA) to consider cumulative exposure (resulting in aggregate and synergistic effects) across different mechanisms of toxicity and different classes of pesticides, including at exposure levels below allowable levels set by the agency.
In the context of the regulatory gaps and pesticide industry influence at EPA (See Daily News here), advocates stress the importance of transitioning land and agricultural practices to organic principles.
Methodology and Results
Background, Goals, Primary Takeaways
This research was led by an international team of experts from various universities and institutes, including European Molecular Biology Laboratory (EMBL), Institut Pasteur, and Heidelberg University (Center for Infectious Diseases, Parasitology Department). The authors received funding from the European Molecular Biology Laboratory, the German Center for Infection Research, and the American Society of Colon and Rectal Surgeons Research Foundation.
“[K]ey traits—such as egg-laying rates— were significantly reduced by some of these molecules at concentrations that are orders of magnitude below sublethal concentrations (),” says the researchers. “Higher temperatures also increased pesticide-induced lethality and behavioral changes (), which emphasizes the need for chemical testing under realistic environmental conditions, especially given rising global temperatures.”
There are several additional notable findings that researchers cite for future study:
- “Our findings highlight that many agrochemicals with high environmental prevalence can induce behavioral changes across insect species, even at sublethal levels.”
- “Therefore, our findings suggest that the next generation of pesticides should be subjected to more comprehensive testing focused on sublethal effects across different representative species. Notably, these types of assays provide more precise data on how to target pest control for medically important vector species without negatively affecting overall insect biodiversity.”
Drosophila larvae
The main insect species of interest in the study was Drosophila melanogaster, acknowledged by researchers as “an insect model system for toxicology studies.” Drosophila was exposed to various chemical residue mixtures at several concentrations (2 mM, 20 mM, and 200 mM) to “assess the effects of these [chemical] molecules on larval behavior, physiology, and fitness.” Concentrations of 20 mM and 200 mM are expected for typical chemical-intensive farming operations, with the lowest concentration being the expected presence of the chemical in nature due to run-off.
To confirm the potential sublethal impacts of pesticides, researchers also tested the larvae with five pesticides at an even lower concentration (0.2 mM). While there was variability in the degree of acute harm caused by the chemicals of focus, researchers determine that “all pesticides significantly affected larval behavior at this lower concentration [of 0.2 mM].” The researchers in this study elaborate on the following conclusions:
- “For example, glyphosate—a widely used herbicide across the world () that is not lethal at 0.2 mM ()—increased the frequency of turns (headcasting) and decreased stops, altering larval trajectories (). Only chlorpyrifos, the most toxic compound (), caused broad changes in protein levels. However, all but 1,2-dibromoethane altered the protein phosphorylation status in the treated larvae ()—including those that are not lethal at the concentration used ().”
- “Although the developmental delay is within the expected variation among natural populations, the effect on egg laying goes beyond the physiological range measured in the above-described wild-type strains.”
An additional area of concern that researchers identify is the heightened potential for damage of insects by pesticides. “[M]any pesticides that showed low lethality (<10%) at 25°C started exhibiting significantly higher lethality when the environmental temperature was increased by just four degrees,” the researchers provide an example. “For example, the insecticide lindane, nonlethal at 0.2 mM at 25°C (0%), became strongly lethal (79%) at 29°C. Although many molecules altered behaviors at 25°C, the changes at 29°C were often radically different.”
The researchers also identified “nonlinear interactions” between a number of the targeted pesticides, “which suggests that synergistic pesticide interactions may be widespread.”
Mosquitoes and Butterflies
The researchers extrapolate their findings beyond one type of house fly to include other “medically and economically relevant species,” including the mosquito Anopheles stephensi and the butterfly Vanessa cardui.
For testing adverse health impacts of pesticide exposure on mosquito populations, the researchers say, “[L]arvae were exposed overnight to varying concentrations of a neonicotinoid (thiacloprid), a pyrethroid (cyhalothrin), and a fungicide (dodine) on multiwell plates followed by recording and tracking their movement ().” “All pesticides caused larvae to move significantly slower at concentrations with negligible or low lethality (),” they continue.
For testing the adverse health impacts of pesticide exposure on butterfly populations, caterpillars consumed food that contained traces of thiacloprid, cyhalothrin, and dodine. “Although only cyhalothrin showed some lethality (), all three molecules affected the movement patterns of the treated caterpillars (),” the researchers conclude.
“These results highlight that sublethal concentrations of pesticides can also affect the behavior of species with high ecological, economic, and clinical relevance.”
Previous Daily News Coverage
Environmental advocates concerned about biodiversity acknowledge the substantial, peer-reviewed scientific literature on ecosystem integrity under threat.
A 2020 report published in Science determined that about one-quarter of the global insect population has died off since 1990. In 2022, researchers in the United Kingdom determined that “58.5% fewer flying insects” were caught on windshield wipers between 2004 and 2021, which they viewed as an indicator of systemic insect and pollinator deaths. In a 2019 study published in Biological Conservation, researchers identified “the dreadful state of insect biodiversity in the world, as almost half of the species are rapidly declining and a third are being threatened with extinction.”
Scientists have spoken out, with over 70 scientists submitting a letter to the editor in Nature Ecology & Evolution in 2020 with a compilation of solutions necessary to curb the impending insect apocalypse. A research report in 2020 published in Nature by scientists at the University College London determined, among various findings, that the interaction between climate change () and high-intensity agriculture diminished total insect abundance by 50%, and species richness by 27%. See a review of recommended policies and practices to safeguard insect biodiversity published in Conservation Science and Practice.
For more information on the link between petrochemical-pesticide reliance and insect die-offs, see the 2019 Pesticides and You report, Study Cites Insect Extinction and Ecological Collapse. Advocates nationwide have called upon Congress and EPA to update pesticide drift protection policy to protect families of farmworkers, schoolchildren, and other vulnerable subpopulations who face disproportionate harms of pesticide exposure. (See Action of the Week here).
Call to Action
Environmental and public health advocates, as well as farmers and fenceline communities, are concerned with the adverse health impacts of long-term pesticide use on their local environments.
“The loss of any insect species impacts overall biodiversity and upsets the balance of critical food webs,” says Sara Grantham, science, regulatory, and advocacy manager at Beyond Pesticides. “There is a wide body of science linking pesticide exposure to negative impacts on insects and other beneficial organisms, which are necessary in providing essential ecosystem services such as pollination. Population effects in these species threaten agricultural productivity and food security, as well as puts us one step closer to the very real threat of insect extinction.”
To access more peer-reviewed scientific literature on biodiversity issues, see the Pesticide-Induced Disease Database on biodiversity, beneficial insects, and pollinators. For more coverage and analysis of scientific literature and policy updates, see the Daily News section on biodiversity here.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Science
