31
Jul
Sublethal Effects of Weed Killer Glyphosate Associated with Colony Decline, According to Study
(Beyond Pesticides, July 31, 2025) A study published in Environmental Advances finds that hundreds of honeybee hives across central and northern Italy are contaminated with various pesticides and their metabolites, including glyphosate and fosetyl.Â
“There was no significant difference in glyphosate presence between dead/dying and live bees, suggesting chronic exposure rather than acute toxicity. However, higher pesticide concentrations in dead/dying bees indicate potential sublethal effects contributing to colony distress,†according to the authors. This peer-reviewed study builds on the mounting evidence outlined in the literature connecting pesticide residues to nontarget harm to pollinators and other insects and animals that are critical to biodiversity.
Background and Methodology
“The primary objectives of this study were to develop and validate a reliable, sensitive method for analyzing polar pesticides [highly soluble in water] in honeybees and to investigate polar pesticides residue levels in honeybees across northern and central Italy,†say the researchers of this study, who conduct research at the Experimental Zooprophylactic Institute of Lombardy and Emilia Romagna “Bruno Ubertini”, Experimental Zooprophylactic Institute of Umbria and Marche “Togo Rosatiâ€, and Experimental Zooprophylactic Institute of Lazio and Tuscany “M. Aleandri.”
314 honeybee samples were gathered voluntarily from local beekeepers in six regions of northern and central Italy—Lombardy, Emilia Romagna, Lazio, Tuscany, Umbria, and Marche. Two sample types—dead or dying bees and live bees from healthy hives—enable a comparison of contamination levels based on bee mortality and sublethal effects. Four pesticides and their associated metabolites are the focus of this study. They include the weed killer glyphosate (its major metabolite/breakdown chemical AMPA [Aminomethylphosphonic acid], N-acetyl-AMPA, and N-acetyl-glyphosate), fosetyl (Phosphonic acid), glufosinate (NAG [N-acetyl-glufosinate] and MPPA [3-Methylphosphonicpropionic acid] and ethephon (HEPA [Ethephon hydroxy]). These pesticides were targeted because they are considered polar pesticides, meaning that they are more challenging to analyze due to their small molecular size and water solubility.
There were two primary analytical tools, LC-MS/MS (Liquid Chromatography-Tandem Mass Spectrometry) and IC-HRMS (Ion Chromatography-High Resolution Mass Spectrometry), used to address this obstacle. The first tool was used in Umbria, Marche, Lazio, and Tuscany to identify the herbicides glyphosate, ethephon, glufosinate, fosetyl, and their metabolites (AMPA, N-acetyl-AMPA, HEPA, MPPA, NAG). Meanwhile, the second tool was used in Lombardy and Emilia Romagna and can also identify N-acetyl-glyphosate and phosphonic acid. Financial support was provided by the Italian Ministry of Health, but otherwise the authors declared “no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.â€
Results and Discussion
The researchers identified eight notable findings in developing their research.
- Glyphosate was found in 33.4 percent of samples, making it the most frequently detected pesticide in this study;
- There was no significant distinction between glyphosate residues in dead/dying bees and healthy, live beehives; however, sublethal effects are possible, considering that average concentrations were higher in the former group;
- Fosetyl contamination was localized to Emilia Romagna and some in Lombardy, with 85 percent of fosetyl-positive samples also containing glyphosate;
- Glufosinate and ethephon were never detected in the samples;
- There was co-occurrence of multiple pesticides, including 16 percent of all samples containing both glyphosate and fosetyl;
- Higher pesticide detection correlated with herbicide-intensive regions;
- This study validated the dual methodology of LC-MS/MS and IC-HRMS since it was the first large-scale application of these methods in Italy; and,
- The health of honeybees can be considered an effective bioindicator when it comes to ecological and human health.
For additional information and analysis, please consider reading the Results and Discussion sections.
Previous Research
A recently published study in Royal Society Open Science shows intraspecific differences (between individuals of a species) in wild bumblebees (Bombus vosnesenskii) exposed to glyphosate, a fungicide (tebuconazole), and an insecticide (imidacloprid), with gut microbiome health as a factor. In collecting 175 individuals of this wild, foraging species from an alpine meadow, a valley lake shoreline, and a suburban park and exposing them to a diet with individual pesticides and mixtures, the researchers assess the varying lethal and sublethal effects that can occur with pesticide exposure. (See Daily News here.) A 2024 research article in Biology Letters, published by The Royal Society, finds that the neonicotinoid insecticide imidacloprid disrupts survival and reproductive patterns in Bombus impatiens bumblebees. The study adds to the wide body of science highlighting how exposure to pesticides “can result in immediate mortality or cause long-term detrimental effects on pollinators‘ health, lifespan and reproductive success,†the authors state. (See Daily News here.) A different novel study published in 2025 in Chemosphere built on existing research of pesticide impacts on honeybee fertility. This study identifies impacts on male fertility in a bee species (Osmia bicornis) with exposure to sulfoxaflor, a systemic sulfoximine insecticide with similar mechanisms to neonicotinoids. “For the first time, we demonstrate that short-term chronic, field-realistic exposure to a common pesticide reduced pre-copulatory display (36%) and sounds (27%) [courtship behaviors], increased the number of copulations (+110%) and the mating duration (+166%), while finally reducing sperm quantity (25%) and mating success (43%),†the researchers report. They continue, “Our research raises considerable concern on the impact of field-realistic, low sublethal pesticide levels on the fertility and reproductive success of pollinators.†(See Daily News here.)
Bees are not the only critical wildlife species at elevated risk. A 2025 study following a mass mortality event of approximately 200 monarch butterflies (Danaus plexippus plexippus) in Pacific Grove, California, highlights the role of pesticides, synthetic pyrethroids in particular, in causing lethal and sublethal effects to nontarget organisms. The research, published in Environmental Toxicology and Chemistry, detects residues of 15 pesticides and associated metabolites in the bodies of 10 deceased butterflies collected from the January 2024 event that occurred near an overwintering site frequented by monarchs.
“On average, each monarch butterfly contained 7 pesticides,†the authors report. They continue, “Notably, three pyrethroid insecticides—bifenthrin, cypermethrin, and permethrin—were consistently detected at or near each chemical’s lethal dose (LD50).†LC50, or Lethal Concentration 50, values represent the concentrations of chemicals lethal to 50% of a test population. (See Daily News here.)
A 2025 study conducted in rural Pennsylvania and published in Environmental Entomology highlights threats to nontarget organisms from neonicotinoid insecticide exposure. Using nine different species of ground beetles as examples, the study documents sublethal behavioral effects as well as decreased week-long survival. “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.†(See Daily News here.)
Call to Action
At the end of this year’s Pollinator Week in June, Beyond Pesticides called on U.S. Environmental Protection Agency (EPA) to meet its obligations under Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and Endangered Species Act (ESA) by facilitating a transition to organic practices, given the unreasonable adverse effects to pollinators associated with pesticide use. If you have not already, you can take this action today! (See Daily News here and Action of the Week here.)
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Environmental Advances
