25
Apr
Male Fertility and Reproduction in Bee Species Threatened with Systemic Insecticide Exposure, Study Finds
(Beyond Pesticides, April 25, 2025) A novel study in Chemosphere finds 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.â€
Mating behaviors and the ability to successfully reproduce determines the survival of species. As the authors state: “Mating disorders may therefore contribute to the recent decline in insect and pollinators’ health worldwide. While the impact of pesticides on pollinators is widely considered as a driving factor for reducing pollinators’ health, their effect on mating behaviour and male fertility remains widely overlooked.â€
The red mason bee (O. bicornis) can “provide essential pollination service for both crops and wild plants sustaining food production and biodiversity while serving as a bioindicator of environmental health.†The abundance and diversity of pollinators has been declining globally, as documented in scientific literature, which puts biodiversity and the production of pollination-dependent crops at considerable risk. The researchers also reference mounting evidence (see here, here, here, and here) that “suggests that environmental pesticide pollution can negatively affect insect biomass and diversity, including bees.â€
They continue by saying: “Pesticides can cause both lethal and sublethal negative effects on bees, individually or in combination with other stressors. These effects include impairments in learning and memory, decision time, feeding behaviour, ovary development, colony functionality, nesting behaviour, immune response, motor functions and phototaxis, respiratory rhythm, thermoregulation, orientation and navigation, and flight abilities. However, our understanding of how pesticide exposure may affect insect mating, fertility and reproductive physiology remains scarce, in particular for solitary bees.†(See studies here, here, here, here, here, here, here, and here.)
Within the study, the experiment was conducted over the course of seven weeks and evaluated mating behaviors that include mating choice, pre-copulatory display, pre-copulatory sound, mating success, post-copulatory display, and post-copulatory vibrations, as well as other behaviors such as food consumption. The results highlight that sulfoxaflor exposure alters the pre-mating behaviors of O. bicornis males and subsequent mating success.
By reducing males’ mating displays and sounds, this lowers the likelihood of males being accepted by females. Observed successful mating also requires almost three times longer for the pesticide-exposed males within the experiment, which could endanger the bees and increase the risk of predation during the process. Â
The authors report: “Overall, there was a significant negative effect of sulfoxaflor on the mating success of male bees, resulting in 43% fewer successes in the pesticide group (50%) as compared to the control group (87%). Consequently, sulfoxaflor exposure significantly reduced the occurrence of post-copulatory display and post-copulatory vibrations… Our novel results demonstrate that sublethal, field-realistic pesticide exposure can turn mating into a long, risky, and unsuccessful process in solitary bees.â€
The data reveals that sulfoxaflor can negatively affect mating behavior, mating success, and male fertility, which is “likely explained by the pesticide altering the central nervous system of bees, thereby impairing their cognitive, sensory, and motor abilities as well as reproductive behaviour and physiology.†(See studies here, here, and here.) The researchers continue, saying: “The observed findings highlight that pesticides can reduce male fitness which may inevitably lead to drastic consequences at the population level. The data offer a plausible mechanistic explanation for the ongoing decline of wild bee populations and underscore the urgent need to find sustainable solutions in agriculture that safeguard pollinators and biodiversity.â€
Behavior impairments not specific to reproduction, such as the observed increased hyperactivity and food consumption, are also of concern, as locomotion and coordination are essential for flight ability and the success of foraging. “[T]he behavioural impairments shown here may impact the quality of the pollination service provided by bees. The increased hyperactivity caused by pesticide-treated bees may have consequently increased bee energy –and thus food – consumption,†the researchers postulate.
As a result, the authors conclude by saying: “We reveal that pesticides alter bee behaviours before, during, and after mating. This may translate to wider fitness impairments, including alterations on the ability of bees to forage, defend territories against competing males, and find females.â€
Previous research supports these findings, which the researchers reference from the following studies:
- Male bees play a key role in sexual reproduction, with any impacts specifically to males having a significant influence on population dynamics and offspring sex ratios. (See study here.)
- “Sulfoxaflor is a sulfoximine insecticide, acting as an agonist of the nicotinic acetylcholine receptors (nAChR). By disrupting the cholinergic signaling on insect’s central nervous system, even low doses can cause uncontrolled nerve impulses and muscle tremors that can affect behaviour and locomotion.†(See studies here, here, and here.)
- “While sulfoximines and neonicotinoids have both been extensively commercialized for broad pest control and share a similar mode of action (i.e., IRAC group 4), sulfoxaflor was reported as more selective and less toxic on sap-feeding pest insects and non-target organisms. Recent evidence however suggests that sulfoxaflor may be more toxic than certain neonicotinoids, such as acetamiprid and thiacloprid.†(See here, here, here, and here.)
- “[S]ulfoxaflor can cause adverse effects on honey bees (e.g., reduced survival and disrupted metabolism), bumble bees (e.g., reduced reproductive success, egg-laying rate, and colony growth), and solitary bees (e.g., reduced survival, flight and foraging performances, feeding behaviour).†(See here, here, here, and here.)
- Pesticides can cause “detrimental effects on the reproductive physiology and fertility (i.e., the capacity to produce viable sperm in males, and viable offspring in females) of honey bees, and bumble bees.†(See here, here, here, here, and here.)
- “Laboratory and semi-field research have assessed the impact of sublethal pesticide exposure on Osmia females, including alterations of ovary development, fecundity and offspring production, sex ratio, and overall population growth rate.†(See studies here, here, here, here, here, here, and here.)
- “[P]revious studies revealed that sulfoxaflor increases oxidative stress that can induce apoptosis [cell death] in honey bee sperm cells.†(See here and here.)
- A study of sublethal concentrations of the fungicide fenbuconazole “demonstrated that pesticide exposure significantly reduced the pre-copulatory sounds frequency of modulation (Hz) in O. bicornis, with a subsequent impairment in their mating success.â€
- Thiamethoxam and clothianidin, both neonicotinoid insecticides, are “shown to impair male acceptance and mating success, and male fertility in Osmia spp [species]; likely translating to considerable negative effects at the population level.†(See here, here, here, and here.)
“Irrespective of the underlying mechanism, a reduction in sperm quantity will have downstream negative consequences on the number of females a male can successfully inseminate,†the authors explain. “Given fewer inseminated females would yield reduced female offspring, our data provide an additional mechanistic explanation for recently observed declines in wild bee populations.†(See studies here and here.)
As previously reported by Beyond Pesticides, exposure to pesticides, even at low concentrations, can compromise pollinator health. A multitude of studies find that exposure affects key traits such as survival, reproduction, learning and memory, flight, and foraging, among others. The risk assessments conducted on pesticides by the U.S. Environmental Protection Agency (EPA) lack comprehensive data regarding their effects on bees. The limited studies that are performed do not adequately assess the varying impacts throughout all bee species, which display differing levels of sensitivity, nor do they account for the cumulative effects through various routes of exposure to pesticide mixtures. (See more on EPA’s failure to protect pollinators here and here.)
“Considering that reproductive traits underpin individual fitness and ultimately population dynamics, it is rather surprising that these traits remain largely overlooked, in particular for bee ecotoxicology,†the researchers say. They continue: “Our research underscores the urgency to include male bees in ecotoxicological assessments to enhance current risk evaluation frameworks. While most research on pesticide impacts focuses on females, particularly in solitary bees, incorporating the neglected male sex in bee health assessments is essential, as impaired male health will inevitably have far-reaching negative consequences at the population-level.â€
As an alternative to harmful chemicals that are improperly regulated and assessed, managing land with organic methods provides a solution with multiple health and environmental benefits. As shared in previous Daily News coverage, studies indicate organic land management “can increase species richness by approximately 34% and abundance by around 50%. Organic farming promotes biodiversity by increasing the abundance and variety of plant and insect species. This, in turn, can lead to enhanced biological control, as more predators can help regulate pest populations,†the authors conclude in a study in Environments.
Promoting ecological balance and restoring biodiversity can be achieved through the elimination of petrochemical pesticides and synthetic fertilizers, and with the adoption of organic practices. Studies show that organic farming has five times higher plant biodiversity and 20 times higher insect species richness compared to conventional farming and that higher biodiversity of insects is seen in fields with genetically diverse crops.
Take action to protect biodiversity and keep organic strong by becoming a member of Beyond Pesticides today. You can also become an advocate for organic parks through the Parks for a Sustainable Future program and make The Safer Choice to avoid hazardous home, garden, community, and food use pesticides.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Vélez-Trujillo, L. et al. (2025) Romance in peril: A common pesticide impairs mating behaviours and male fertility of solitary bees (Osmia bicornis), Chemosphere. Available at: https://www.sciencedirect.com/science/article/pii/S0045653525002772.
