05
Jun
Study Adds to Findings of Neonic Insecticides’ Threat to Soil Communities; Ground Beetles at Risk
(Beyond Pesticides, June 5, 2025) A study conducted in Pennsylvania and published in Environmental Entomology highlights threats to nontarget organisms from neonicotinoid insecticide exposure. Using species of ground beetles as an example, the study documents sublethal behavioral effects as well as decreased week-long survival. This research fills a notable gap in current research, with the authors explaining, “Predatory soil arthropods are under-represented in insecticide toxicity studies, severely limiting our understanding of how insecticides affect soil-invertebrate communities in agroecosystems.”
The researchers continue, “As a step toward addressing this issue, we conducted novel acute oral, topical, and soil-based toxicity assays on 9 ground beetle species (Coleoptera: Carabidae) in response to the neonicotinoid insecticides clothianidin, thiamethoxam, and imidacloprid.” The nine carabid beetle species, all common to agroecosystems in central Pennsylvania, were exposed to clothianidin, while additional assays with thiamethoxam and imidacloprid were conducted on the two most abundant species.
A wide body of science exists that connects neonicotinoid exposure to health effects in a variety of nontarget organisms. Neonicotinoids, a class of neurotoxic insecticides, act as agonists of nicotinic acetylcholine receptors, “persist under field conditions, and are water soluble, enabling them to translocate into plants and provide systemic protection of seedlings,” the researchers note. They continue, “[T]hese insecticides pose a risk to resident macrofauna, such as ground beetles (Coleoptera: Carabidae), which spend most of their lives in and around soil.” (See studies here and here.)
With the lack of dose–response data for the vast majority of soil macrofauna, the authors say there is “a need to generate basic toxicity data for additional species of soil macrofauna, especially those that are at high risk to multiple routes of insecticide exposure.” Beetles represent approximately 40% of all described insects, making them the largest order of insects and encompassing ~25% of all known animal species on Earth.
As previously reported by Beyond Pesticides in the Daily News post from June 23, 2023, Ecosystem Critical to All Pollinators: Popular and Unpopular Pollinator Guide, beetles are frequently overlooked in the world of pollinators. Gardeners are often familiar with the beneficial pest-control services provided by ladybugs and predaceous ground beetles, but flower-visiting species like soldier beetles, scarabs, long-horned beetles, sap beetles, and checkered beetles all provide important pollination services that complement the work of other pollinators in the landscape.
According to the U.S. Department of Agriculture’s Forest Service, beetles were some of the earliest insects to utilize flowers for food and habitat. In doing so, these ancient pollinators began an important collaboration between flowers and beetles that continues today. Mature beetles feed on the pollen of flowering plants. They pollinate as they feed, transporting pollen on their body from a previous flower to successive locations. Idaho State University notes that beetles play a more important role in the pollination of tropical regions than in temperate ones. Even so, there are approximately 50 native plant species in the U.S. and Canada that depend upon beetle pollination.
Carabid beetles, the target of the current study, are, according to the researchers, “some of the most common predaceous, soil macrofauna found in Mid-Atlantic agroecosystems, and they are active throughout the growing season.” (See study here.) This causes these beetles to frequently encounter neonicotinoids through multiple exposure routes.
“In systems where neonicotinoids are applied to leaves (i.e., foliar sprays on many vegetable crops), carabids may experience topical exposure at rates up to 100 to 1,000 ng [nanogram] of active ingredient,” the authors say. They continue: “In field crops like maize and soybeans, neonicotinoids are more commonly applied as seed treatments, which would appear to reduce topical exposure to nontarget insects but do not eliminate exposure to contaminated soil or food. Soil concentrations of neonicotinoids generally stay below 100 ppb [parts per billion], but concentrations of neonicotinoids have been measured up to 594 ng g−1 in surface soil (0 to 5 cm) after planting thiamethoxam-treated soybean seeds.” (See studies here, here, and here.)
Therefore, consuming contaminated prey may present the greatest exposure risk for carabid beetles. “Beyond exposure via nontarget invertebrates, there is also a risk that predatory taxa will encounter insecticide residues when scavenging dead herbivores and when attacking herbivores that have developed resistance to neonicotinoids—this last scenario will only become more likely as more pest species evolve resistance,” the researchers state. (See research here and here.)
The study was conducted at Penn State’s Russell E. Larson Agricultural Research Center in Rock Springs, PA. The collected carabid species used for the soil-exposure, oral, and topical assays include Amara familiaris, Anisodactylus sanctaecrucis, Chlaenius tricolor, Harpalus pensylvanicus, Notiobia terminata, Patrobus longicornis, Poecilus chalcites, Poecilus lucublandus, and Pterostichus melanarius.
“Insecticide doses were directly applied to beetle pronotums [dorsal plate/first segment of the thorax] for topical assays, to dried cat food for oral assays, and to soil for soil-contact assays,” the authors say. Twenty-four hours after dosing, beetles were assessed and categorized as dead (D), exhibiting a toxic response (T), or apparently healthy (A).
“A beetle was assumed dead if it did not respond to gentle prodding or flipping with forceps,” the researchers specify. “If a beetle was responsive but exhibiting a sublethal toxic response (slow/erratic moving, repetitive twitching of legs and antennae, or unable to right itself when flipped over), we recorded it as exhibiting a sublethal, neurotoxic response (T).” Feeding rates and week-long survivorship were also analyzed.
While the field-realistic oral, topical, and soil-based exposure to the neonicotinoids “rarely led to acute (<24 h) beetle mortality,” the study reveals “significant sublethal effects—changes to mobility and feeding behavior—and decreased week-long survival. Under field conditions, carabids exposed to neonicotinoid sprays or contaminated food will be at higher risk of mortality from other factors (e.g., predation and starvation), which may affect their ability to contribute to biocontrol in agroecosystems,” the authors summarize.
“Based on this current study, neonicotinoid sprays and seed treatments are likely to have acute, sublethal effects on carabid beetles when applied at label-recommended rates,” the study concludes. “While neonicotinoid use is unlikely to cause direct, acute (<24 h) losses to carabid populations, exposure is likely to reduce feeding activity and longer-term (>7 d) carabid survival.”
Previous related research finds that field-realistic levels of clothianidin and thiamethoxam are acutely lethal to adult beetles of the Dalotia coriaria species. Another study links oral exposure of imidacloprid to feeding impacts on the isopod Porcellio scaber, while additional research suggests “that contaminated food, not soil, is the primary risk that soil- and seed-applied neonicotinoids pose to carabid beetles.” (See studies here, here, and here.)
As Beyond Pesticides shared in Neonic Insecticide Impairs/Kills Beetle Listed as Threatened and Important to Ecosystem Health, But Not Protected, a study earlier this year in PLOS One finds acute and chronic impacts of nontarget toxicity on a species listed as threatened by the U.S. Fish and Wildlife Service (USFWS), 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, similar to the present study. Burying beetles, specifically, 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.
Shared in other Daily News coverage (see here and here), a 2015 study looks at the detrimental effects of neonicotinoids on molluscan herbivores and their nontarget insect predators, finding that slug exposure to neonicotinoids results in the secondary poisoning of beneficial predatory beetles. The use of these chemicals is not only dangerous to the environment but also puts farmers at economic risk. Research finds that their use can undermine pest control efforts and cause trophic cascades. One study found that when applied to seeds in an attempt to prevent pest slugs from eating seedlings, slugs were unaffected by neonicotinoid toxicity. However, they accumulated the chemicals in their body, and their main predator, beetles, died after consuming them. By creating an ecological imbalance, neonicotinoids allow the pest slugs to proliferate and alter the entire ecosystem. (See more in the Daily News post titled, Study Cites Insect Extinction and Ecological Collapse.)
As a holistic solution, organic land management practices can be adopted. As stated in Organic Systems: The Path Forward, organic practices support and enhance biodiversity and allow for healthy ecosystems to flourish without the use of toxic chemicals. Protecting all species, including pollinators and other organisms that provide ecosystem services, 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. Learn more about the benefits of organic agriculture here and here, as well as how to create nontoxic lawns and landscapes in your community with the Parks for a Sustainable Future program.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Pearsons, K. and Tooker, J. (2025) Acute toxicity of neonicotinoid insecticides to ground beetles (Coleoptera: Carabidae) from Pennsylvania, Environmental Entomology. Available at: https://academic.oup.com/ee/advance-article-abstract/doi/10.1093/ee/nvaf048/8128784.
