The contribution of neonicotinoid pesticides to bee colony collapse disorder.
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The Contribution of Neonicotinoid Pesticides to Bee Colony Collapse Disorder
Introduction to Neonicotinoid Pesticides and Bee Health
Neonicotinoid pesticides, introduced in the early 1990s, have become one of the most widely used classes of insecticides globally. These chemicals are known for their broad-spectrum activity and low mammalian toxicity, making them popular in agricultural practices. However, their systemic nature, which allows them to be absorbed and transported throughout the plant, including pollen and nectar, poses significant risks to pollinators such as honeybees and bumblebees .
Sub-lethal Effects on Bee Health
Research has shown that sub-lethal exposure to neonicotinoids can have numerous adverse effects on bee health. These include impaired foraging behavior, reduced brood development, and neurological or cognitive impairments, all of which can contribute to colony collapse disorder (CCD) . For instance, bees exposed to low levels of neonicotinoids exhibited reduced foraging success and homing ability, leading to increased mortality due to homing failure .
Impact on Queen Bees
The health of queen bees is crucial for the survival and productivity of bee colonies. Studies have demonstrated that neonicotinoid exposure can severely affect queen bees' reproductive anatomy and physiology, leading to reduced queen success and colony performance . This includes compromised ovaries and lower quality and quantity of stored sperm, which are essential for the queen's reproductive success.
Synergistic Effects with Pathogens
Neonicotinoids not only affect bees directly but also interact synergistically with common microbial pathogens, exacerbating their impacts. For example, the combination of neonicotinoids and pathogens like Nosema ceranae and black queen cell virus (BQCV) significantly increases bee mortality. These interactions can elevate viral loads and enhance the deleterious effects of pathogens, further contributing to colony losses .
Long-term Colony Performance
Chronic exposure to neonicotinoids has been linked to long-term detrimental effects on colony performance. Studies have shown that colonies exposed to neonicotinoids over multiple brood cycles exhibit decreased numbers of adult bees, reduced honey production, and impaired pollen collection. Additionally, neonicotinoid exposure has been associated with queen supersedure, where the queen is replaced due to her reduced performance, which can destabilize the colony.
Winterization and Colony Collapse Disorder
Sub-lethal exposure to neonicotinoids has also been found to impair the winterization process of honeybee colonies, a critical period for their survival. Research indicates that neonicotinoid-treated colonies are more likely to abandon their hives during winter, leading to symptoms resembling CCD. In contrast, control colonies without neonicotinoid exposure showed better winter survival and re-population with new bees.
Conclusion
The evidence clearly demonstrates that neonicotinoid pesticides contribute significantly to bee colony collapse disorder through a combination of direct and indirect effects. These include impaired foraging and reproductive success, synergistic interactions with pathogens, and long-term impacts on colony performance and winter survival. Given the critical role of bees in pollination and ecosystem services, there is an urgent need to reassess the use of neonicotinoids and explore pollinator-friendly alternatives to ensure the sustainability of bee populations and the services they provide.
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