05
Feb
Neonic Insecticide Impairs and Kills Beetle Listed as Threatened and Important to Ecosystem Health, But Not Protected
(Beyond Pesticides, February 5, 2025) A study in PLOS One finds acute and chronic impacts of nontarget toxicity on the American burying beetle, Nicrophorus americanus, with neonicotinoid insecticide exposure. In assessing environmentally relevant concentrations of the neonicotinoid insecticide imidacloprid with N. americanus, the researchers note both mortality and behavioral effects that leave the species at high risk of predation. These effects mean the American burying beetle “may be at greater risk to insecticide exposure than previously thought and vulnerable to episodic, low-dose neonicotinoid exposure,†the authors say. This data sheds important light on a species that has been listed by the U.S. Fish and Wildlife Service (USFWS) as threatened.
Burying beetles provide important ecosystem services within the environment such as “burying carrion, increasing available nutrients in soil, and expediting carrion decomposition, while acting as a food source for secondary consumers,†the researchers state. (See more on ecosystem services and beneficial insects here, here, and here.) The N. americanus species are habitat generalists and can be found in grasslands, wet meadows, and forested areas that neighbor agricultural lands and introduce the beetles to pesticide drift and soil residues.
While acute and chronic effects vary in duration and severity, pesticide exposure resulting in both of these “cause[s] negative impacts on beneficial terrestrial insect taxa,†the researchers state. They continue, “Beyond mortality, behavioral indicators of toxicity are often better suited to assess sublethal effects of residual concentrations in the environment.â€
An assessment of low levels of imidacloprid in N. americanus shows how “sublethal levels can result in a wide range of detrimental behavioral effects at the population-level, which may increase mortality from predation in natural settings. Behaviors associated with feeding, predator avoidance, mobility, sensory perception, and navigation are among the most affected by neurotoxic compounds, as they are linked to insect neurophysiology and biochemistry.â€
While various other studies (see here, here, and here for examples) document behavioral effects in insect species with neonicotinoid exposure, the authors find that “few studies report the impacts of neonicotinoids, both lethal and sublethal endpoints, on nontarget beetle taxa.†This study is novel in that it provides the first neonicotinoid toxicity data for a species of burying beetles that are currently inadequately protected in North America.
The authors state: “Prior to N. americanus being listed as an endangered species, researchers suggested that the widespread use of dichlorodiphenyltrichloroethane (DDT) may have initially contributed to steep population declines. Since then, few studies have discussed or even considered the toxicity of specific insecticide active ingredients to N. americanus.â€
Studying the impacts of this pesticide exposure on various species is vital, as taxa-specific sensitivity can occur. This has been documented in bee species (see Daily News coverage here), as well as in a previous beetle study with imidacloprid. In the study, soldier beetles are documented as being ten times more sensitive to neonicotinoids than ladybird beetles. This highlights an important deficiency in current risk assessments, as model species used do not represent all species that can experience nontarget pesticide exposure. See more on U.S. Environmental Protection Agency (EPA) failures here, here, here, here, and here.
The researchers report: “Once common across eastern North America, N. americanus distribution has reduced by more than 90%, remaining in only six states with the largest populations concentrated in Oklahoma and Nebraska. [USFWS] first listed N. americanus as an endangered species in 1989; however, the USFWS recently reclassified N. americanus as threatened in 2020, citing a diminished threat of extinction in its current range.â€
They continue: “Current and historical causes of N. americanus decline include habitat loss to agricultural and urban development, changes in the availability of carrion resources (birds and small mammals), light pollution, and pesticide use… However, concurrent risks of nontarget pesticide exposure to N. americanus were not included in the Species Status Assessment.†This led the authors to design a study assessing neonicotinoid exposure in the American burying beetle.
The study itself uses four nominal concentrations including a control group and groups exposed to 60, 120, and 240 ng/µL solutions of imidacloprid. The treatment groups are subjected to either single LD10 doses or repeated LD10 doses (two separate LD10 doses 48 hours apart). As a result, the researchers find both effects of mortality and behavioral impairments in N. americanus beetles.
“Over a ten-day period of monitoring, N. americanus experienced 30% mortality after a single exposure to the nominal LD10 and repeated exposure caused an increase to 50% mortality, supporting time-cumulative toxicity of this class of insecticides,†the authors report. They continue, “Beyond mortality, our data demonstrate significant behavioral alterations after a single and repeated LD10 application of imidacloprid, which may put N. americanus at greater risk of starvation, desiccation, or predation.â€
In noting erratic movement after low level imidacloprid exposure, the researchers highlight how behavioral responses are key factors that should be considered with environmental risk assessments. “Behavior is fundamentally linked to individual fitness, which may influence population level effects, and is a sensitive indicator of pesticide exposure,†they state. “In the present study, behavioral responses of imidacloprid-exposed beetles were significantly different from the controls, with a single LD10 dose prompting greater distance traveled and at greater velocity than repeated LD10 doses,†the authors summarize.
Neonicotinoid insecticides are broad-spectrum pesticides that “represent the largest market share of any insecticide class at 27% worldwide with at least 140 crop uses,†the researchers note. “Specifically, neonicotinoid-coated seed treatments are the most widely adopted crop protection strategy, especially for common field crops. However, it is estimated that greater than 90% of the neonicotinoid active ingredient applied could move from the site of application via runoff and/or particulate matter.â€
With neonicotinoids being transported in runoff and persisting in soil, this subjects nontarget organisms, such as the American burying beetle, to sublethal effects and mortality. According to the authors, “Depending on the soil characteristics and light exposure, neonicotinoid active ingredients can bind and persist in soil for months or years, potentially leading to incidental soil contact and soil-water ingestion by burying beetles.†(See studies here and here.)
As the researchers conclude, “Under the Federal Insecticide, Fungicide, and Rodenticide Act [FIFRA], the US EPA is responsible for ensuring that registered pesticide use does not cause unreasonable adverse effects on the environment, including listed species and their critical habitats; however, the US EPA has yet to meet the Endangered Species Act criteria for over 95% of all registered pesticides.†EPA must be required to properly assess all current and future pesticides for not only impacts on beneficial species that provide ecosystem services but all wildlife.
To ensure that EPA stands up to the standards of FIFRA and protects health and the environment, participate in the “EPA Must Review Complete Data for All Pesticides†Action of the Week before February 10. Additionally, a better solution to toxic chemicals exists with organic land management and also needs to be considered in these risk assessments. The holistic approach with organic practices provides a healthy alternative to the detrimental effects of chemicals that pollute the environment and all organisms within it.
Protecting all beneficial species, including pollinators, from pesticides is crucial to agricultural and economic productivity, as well as food security. Take action to advance organic, sustainable, and regenerative practices and policies and be part of the organic solution by becoming a member of Beyond Pesticides today.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Cavallaro, M. et al. (2025) Neonicotinoid exposure causes behavioral impairment and delayed mortality of the federally threatened American burying beetle, Nicrophorus americanus, PLOS One. Available at: https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0314243.
