Molecular Pathogens 2024, Vol.15, No.3, 129-141 http://microbescipublisher.com/index.php/mp 132 3 Impact of Pesticides on Honeybees Pesticides, particularly neonicotinoids, have been identified as a significant threat to honeybee populations. These chemicals can have various detrimental effects on bees, ranging from acute toxicity to more subtle, sublethal impacts on behavior and physiology. Additionally, the interaction of pesticides with other environmental stressors can exacerbate their harmful effects. 3.1 Types of pesticides Neonicotinoids are the most widely used class of insecticides globally and pose a major threat to bees (Arce et al., 2017). These systemic pesticides, including imidacloprid, thiamethoxam, and clothianidin, are commonly found in nectar and pollen, leading to direct exposure for foraging bees (Chan and Raine, 2021). Other pesticides, such as the novel butenolide insecticide flupyradifurone (FPF), also act as nicotinic acetylcholine receptor (nAChR) agonists and have been shown to have adverse effects on bee health (Cabirol and Haase, 2019; Tosi et al., 2019). 3.2 Acute and chronic toxicity Both acute and chronic exposures to pesticides can negatively impact honeybees. Acute exposure often involves high doses over a short period, while chronic exposure involves lower doses over extended periods. Studies have shown that field-realistic doses of neonicotinoids can significantly reduce bee survival rates and affect their behavior and physiology (Stanley et al., 2016; Tosi et al., 2017). For instance, imidacloprid exposure has been linked to reduced nest initiation and offspring production in solitary bees (Chan and Raine, 2021). 3.3 Sublethal effects on behavior and physiology Sublethal doses of pesticides can have profound effects on bee behavior and physiology. These include impairments in learning and memory, reduced foraging efficiency, and altered social behaviors. For example, exposure to imidacloprid has been shown to reduce nursing behavior in bumblebees (Crall et al., 2017). Additionally, sublethal doses of neonicotinoids have been found to affect learning and memory in bees, which can reduce their foraging efficiency and overall colony health (Siviter et al., 2018). 3.4 Synergistic effects with other stressors The interaction of pesticides with other environmental stressors, such as nutritional deficiencies and pathogens, can amplify their harmful effects. For instance, the combination of poor nutrition and pesticide exposure has been shown to synergistically reduce bee survival and food consumption (Tosi et al., 2017). Similarly, the interaction between neonicotinoids and microbial pathogens like Nosema ceranae can significantly elevate bee mortality rates (Doublet et al., 2015). These synergistic effects highlight the need for comprehensive risk assessments that consider multiple stressors simultaneously (Tosi et al., 2019). 4 Environmental Changes and Their Effects 4.1 Habitat loss and fragmentation Environmental changes have profound impacts on honeybee populations, influencing their health, behavior, and survival. Habitat loss and fragmentation are significant drivers of honeybee population declines. The reduction of semi-natural habitats has led to a scarcity of floral resources and nesting sites, which are crucial for bee survival. Agricultural intensification and urbanization have further exacerbated this issue by converting diverse landscapes into monocultures and urban areas, thereby limiting the availability of diverse pollen and nectar sources (Goulson et al., 2015). The loss of habitat not only reduces the quantity of food available to bees but also affects the quality and diversity of their diet, which is essential for their health and resilience against other stressors (Requier et al., 2015; Jones et al., 2021). 4.2 Climate change Climate change poses a multifaceted threat to honeybee populations. Alterations in temperature and precipitation patterns can disrupt the synchrony between bee emergence and flower blooming, leading to mismatches in the availability of floral resources when bees need them the most (Belsky and Joshi, 2019). Additionally, climate change can exacerbate the spread of pests and pathogens, further stressing bee populations. For instance, warmer
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