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Insecticides, while effective in controlling crop damage from pests, pose significant risks to beneficial insect populations, including vital pollinators. A recent investigation led by scholars at Penn State has uncovered how even minimal doses of these chemicals can detrimentally affect pollinators by interfering with their mating behaviors.
The findings, published in the journal Science of The Total Environment, specifically evaluated the impact of imidacloprid, a neonicotinoid insecticide that ranks among the most commonly utilized worldwide.
Researchers discovered that even at sublethal levels, imidacloprid exposure led to decreased mating success in bumble bees, along with alterations in chemical communication among both male bees and gynes, the reproductive females. Furthermore, the study highlighted decreased sperm viability in males and diminished fat reserves in gynes.
Nathan Derstine, a postdoctoral scholar within the College of Agricultural Sciences, emphasized the importance of these results for guiding future investigations and for assessing the trade-offs associated with pesticide application in agricultural systems. He stated, “As pest control remains a critical element of food production, it is essential to explore innovative pesticides or integrated pest management strategies that protect pollinator populations without adversely affecting crop yields.”
Pollinator populations, like bees, are currently experiencing global declines attributed largely to the use of pesticides, particularly neonicotinoids. These chemicals can linger in the environment—specifically in soil, pollen, and nectar—creating multiple avenues for pollinator exposure after application.
Etya Amsalem, an associate professor of entomology and co-author of the study, noted that while extensive research exists on the effects of pesticides on pollinators, much of it tends to focus on immediate, short-term consequences.
“This study aims to explore fitness outcomes that may not be obvious at first but can significantly impact population dynamics over time, such as impaired mating and disturbed chemical communication,” Amsalem explained.
In their experimental setup, Derstine and his team subjected bumble bees to very low concentrations of imidacloprid in a controlled environment. The bees had access to sugar water infused with either six or 60 parts per billion of the insecticide for three days, reflective of real-world exposure levels.
Subsequently, researchers assessed the mating interactions by introducing gynes, both exposed and unexposed to the insecticide, to male bees. They repeated the experiment by reversing the exposures, placing males with females under similar conditions.
To further understand the pesticide’s influence on chemical signaling, the researchers evaluated potential sex pheromone compounds from the surface of both males and gynes, as well as from their pheromone-producing glands.
“We also aimed to determine if pesticide exposure impacted the physiological aspects of both genders, measuring sperm viability in males and fat reserves in gynes,” said Derstine. “Low sperm viability can hinder colony performance, while gynes depend on their fat reserves to survive the winter and establish new colonies in the spring.”
Analysis revealed that the negative effects of imidacloprid were more pronounced in female bees. Despite their larger body size, gynes had comparable pesticide levels to males, and while male bees tended to avoid treated gynes, the gynes did not exhibit similar avoidance behavior towards treated males.
Nonetheless, exposure to imidacloprid produced significant declines in male reproductive capacity, reducing sperm count and viability by 41% and 7%, respectively, at the 60 parts per billion concentration.
Amsalem remarked that these findings raise significant concerns about the broader implications of neonicotinoids on pollinator health. She argued that while survival and reproduction metrics are vital initial indicators of ecological harm from pesticides, they likely reveal just a fraction of the overall impact.
“The effects of many pesticides are nuanced, often imperceptible, and difficult to quantify,” she stated. “To truly understand the risks, comprehensive assessments must include extensive long-term and mechanistic studies that shed light on the full range of pesticide impacts.”
Co-authors Cameron Murray and Freddy Purnell, both undergraduates at Penn State during the study, contributed significantly to the research. This work was supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture.
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