{"id":41842,"date":"2026-06-18T00:01:57","date_gmt":"2026-06-18T04:01:57","guid":{"rendered":"https:\/\/beyondpesticides.org\/dailynewsblog\/?p=41842"},"modified":"2026-06-16T16:20:48","modified_gmt":"2026-06-16T20:20:48","slug":"registered-pesticides-toxic-to-honey-bee-larvae-study-finds","status":"publish","type":"post","link":"https:\/\/beyondpesticides.org\/dailynewsblog\/2026\/06\/registered-pesticides-toxic-to-honey-bee-larvae-study-finds\/","title":{"rendered":"Registered Pesticides Toxic to Honey Bee Larvae, Study Finds"},"content":{"rendered":"

(Beyond Pesticide<\/em>s, June 18, 2026) In a study comparing pesticide active ingredients (isolated single chemicals) with full pesticide product formulations containing added ingredients (the packaged products that can contain carriers, sticking agents, emulsifiers, etc.), researchers find the full formulation to be generally more toxic. The research evaluates acute and chronic exposures of four mosquito adulticide active ingredients (AIs), three product formulations, and one biological larvicide pesticide formulation containing Bacillus thuringiensis israelensis<\/em><\/a> (Bti) on honey bee larvae in vitro and finds that three of the four exceed levels of concern (LOCs) set by the U.S. Environmental Protection Agency (EPA). EPA publishes Guidance for Assessing Pesticide Risks to Bees <\/a>in which it identifies levels of harm. The scientists who conducted the study, published in Environmental Challenges<\/em><\/a>, are based at the University of Florida and Auburn University.<\/p>\n

This study references Bti (Vectobac12AS) as the least toxic product, since the acute LD50<\/sub> (lethal dose that kills 50% of the test population) is well below EPA-set LOCs. However, the study only focused on whether Bti harms honey bees. In contrast, there are some indications of its potential adverse effects on other beneficial insects, moths, and butterflies (see fact sheet here<\/a>) and aquatic life, including studies (see here<\/a> and here<\/a>) indicating Bti-induced reductions in benthic macroinvertebrate communities in freshwater bodies (specifically chironomids, or non-biting midges) that serve as biological indicators of water quality and compounding climate impacts.<\/p>\n

The study does not assess the impacts of spinosad<\/a>-based mosquito adulticides, another widely used \u201cbiological\u201d pesticide with demonstrable adverse effects on nontarget organisms, as indicated by the ecological risk assessment<\/a> conducted by the U.S. Forest Service for the active ingredient published in 2016. There is also evidence of adverse impacts on aquatic life, including oxidative stress, as identified in a recent scientific report. (See here<\/a>.) Additionally, a recent study published in 2026 (see here<\/a>) finds that sublethal doses of spinosad can impact the flight capabilities of honeybees.<\/p>\n

While the degree of ecosystem disruption caused by mosquito control products varies considerably by chemical, the harm caused to organisms at any level elevates the need for alternative strategies. Critical to the protection of public health and the environment is the adoption of source reduction programs that reduce or eliminate mosquito breeding sites and public education on the importance of practices that reduce insect bites with the use of repellents, proper clothing, and other preventive techniques.<\/p>\n

Methodology and Main Findings<\/h2>\n

The researchers tested four adulticide active ingredients (chlorpyrifos<\/a>, naled<\/a>, prallethrin<\/a>, sumithrin<\/a>), three commercial formulations (chlorpyrifos-based Mosquito Mist II, naled-based Dibrom, and Duet, which contains prallethrin, sumithrin, and a synergist called piperonyl butoxide<\/a>), and Vectobac12AS\u2014a Bti-based larvicide formulation.<\/p>\n

They split up the testing between acute and chronic exposure buckets for each compound. The first approach was to test a single dose in the diet on day 3 of the larval developmental stage in terms of calculating the lethal dose that eliminated 50 percent of the population (LD50<\/sub>). The second approach was to conduct repeated dosing across days 2-5 to assess the no-observed-adverse-effect-dose (NOAEDs)\/lowest-observed-adverse-effect-dose (LOAEDs). Researchers determined the risk quotient (RQ) for each compound through EPA\u2019s BeeREX tool in their screening-level risk assessment. They note that the RQs are deliberately conservative since, among other factors, \u201cin colonies, larvae are fed by nurse bees, and this may dilute residues through food processing and selective foraging, potentially altering exposure magnitude and bioavailability.\u201d Acetone (1-2 percent) or water were used as solvents \u201cto accommodate the higher stock solution volumes needed for single-dose exposure, while remaining below levels known to affect larval survival or feeding.\u201d<\/p>\n

In terms of the main findings for isolated active ingredients, naled is the most acutely toxic to larvae, with the researchers finding that this AI is roughly 147 percent more toxic than chlorpyrifos. However, researchers flag that none of the four active ingredients exceed the LOC for acute or dietary risk within the context of field-detected pollen or nectar residue levels\u2014otherwise considered low risk based on this regulatory approach.<\/p>\n

However, three of the four adulticide formulations exceed one or both levels of concern. Dibrom (naled) breaches both thresholds, and Mosquito Mist II (chlorpyrifos) exceeds the chronic threshold, but not the acute threshold. The results for Duet are concerning, given that the RQs remain under both acute and chronic thresholds according to EPA-set levels and yet are still documented as highly toxic to larvae in the dose-response assays.<\/p>\n

There are some notable citations that the researchers incorporate into the study that may be of value, not only from the advocacy perspective, but also in terms of literature gaps and opportunities for future scientific exploration:<\/p>\n