Pesticides can safeguard crops from pesky pests; however, they also endanger helpful insects like pollinators. Research headed by scientists at Penn State reveals that even small amounts of pesticides can harm pollinators detrimentally by interfering with their reproductive behavior.
The study, published in the journal Environment Science in Totality , examined the impacts of imidacloprid, a neonicotinoid pesticide that is one of the most extensively utilized insecticides worldwide.
The study revealed that even low levels of exposure to the insecticide decreased successful mating among bumble bees and interfered with the chemical communication in both male bees and gynes—the reproductive female bees. Additionally, this exposure had adverse effects on sperm quality in males as well as fat storage in gynes.
Nathan Derstine, a postdoctoral researcher at the College of Agricultural Sciences, mentioned that these discoveries might guide upcoming studies and assist in assessing the advantages and disadvantages of using pesticides within agricultural ecosystems.
"Pest control plays a vital role in food production, so discovering new types of pesticides or adopting integrated pest management strategies that protect pollinators without harming crops will be essential," he stated.
According to Derstine, pollinators like bees are experiencing worldwide population decreases, with pesticides—particularly neonicotinoids—being major culprits. Once these chemical substances are used on seeds or crops, they linger in the soil, pollen, and nectar, providing various pathways for pollinators to encounter them.
Etya Amsalem, an associate professor of entomology and a co-author of the study, mentioned that although pesticides' impact on pollinators has been widely researched, the emphasis typically lies on noticeable short-term consequences.
Amsalem stated that their focus for the study was on assessing fitness outcomes that aren’t readily noticeable and require time to impact population health and size, such as compromised mating abilities and disrupted chemical communication.
To study how imidacloprid impacts bee mating habits, Derstine mentioned that him along with the other scientists placed bumblebees in a laboratory setting and exposed them to minute quantities of this pesticide. Over a span of three days, the group provided bees with sugar water containing levels of imidacloprid at six or sixty parts per billion—amounts reflective of those found naturally outside controlled environments.
Following this, the scientists selected gynes that had either encountered the insecticide or remained untouched and paired them with male bees to assess if the exposure influenced their mating behavior. Subsequently, they reversed the setup by introducing males that had been exposed or unexposed to pesticide alongside female bees for observation.
The team was equally interested in determining whether pesticide exposure might affect chemical communication within the species. Therefore, the scientists quantified possible sex pheromone substances extracted not only from the outer bodies of both male individuals and gynes but also from the glands responsible for producing these pheromones.
We were curious whether pesticide exposure affected the physiology of both males and females, so we assessed sperm viability in males and checked the fat stores of the gynes," Derstine explained. "Diminished sperm quality can impair the queen’s ability to establish a thriving colony, and the gynes depend on their fat reserves to survive the winter and initiate a new colony come springtime.
Following an analysis of the data, the researchers discovered that exposure to the insecticide appeared to impact female bees more significantly. Despite gyne bees typically being over three times bigger than male bees, they exhibited comparable levels of pesticides within their bodies. Interestingly, while male bees steered clear of pesticide-treated gyner bees, the reverse was not observed; the gyner bees showed no avoidance towards males exposed to the insecticide.
Nevertheless, males exposed to imidacloprid experienced a decline; the pesticide decreased the overall sperm count and sperm viability in the 60 parts per billion group by 41% and 7%, respectively.
Amsalem stated that when combined, these findings contribute to increasing worries regarding the impact of neonicotinoids on pollinator well-being. She further noted that although indicators like survival rates and reproductive success offer a valuable beginning for assessing the environmental harm inflicted by pesticides, they probably signify just the surface level of the problem.
As she explained, many pesticide effects are nuanced and not easily noticeable, frequently presenting challenges for quantification." She continued, "To fully understand the impact of pesticides, comprehensive risk evaluations must include additional long-term and mechanism-based research.
Cameron Murray and Freddy Purnell, who served as undergraduate research assistants at Penn State during the study period, were also contributors to this paper.
More information: Nathan Derstine and colleagues found that sublethal pesticide exposure reduces mating and interferes with chemical communication in a helpful pollinator. Environment Science: The Total Approach (2025). DOI: 10.1016/j.scitotenv.2025.179005
Furnished by Pennsylvania State University
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