Abstract:
The widespread use of herbicides like paraquat and glyphosate in African agriculture poses a significant threat to native pollinators, yet current environmental risk assessments primarily rely on data from European honeybee subspecies. This study investigates the physiological and molecular impacts of these two common herbicides on the African honeybee subspecies, Apis mellifera scutellata Lepeletier. We conducted a randomized controlled trial with 41,400 bees, exposing them to concentrations mimicking field application rates to assess both acute and chronic exposure effects. Key indicators of bee health, including survival rates, sucrose consumption, gut microbiota composition, oxidative stress gene expression, and bee adaptability responses to the herbicides, were measured. Our findings reveal that both paraquat and glyphosate reduce bee survival and sucrose consumption in a dose-dependent manner (p < 0.05). Notably, African honeybees demonstrated a heightened susceptibility to paraquat, with an oral lethal dose (LD50) of 10.8 µg/bee, equivalent to 0.2 µg/mg of bee weight. This is significantly lower than the 0.5 µg/mg reported for European subspecies, highlighting a critical gap in current risk assessments. However, it was more tolerant to glyphosate with an oral lethal dose (LD50) of 229.5 µg/bee, equivalent to 3.4 µg/mg of bee weight. This is significantly higher than the 1.0 µg/mg reported for European subspecies, also highlighting a critical gap. At the molecular level, both herbicides severely disrupted the honeybee gut microbiome, decreasing the relative abundance of beneficial bacteria, including Gilliamella apicola, Snodgrassella alvi, Frischella perrara, and Lactobacillus species (p < 0.05). This dysbiosis was accompanied by oxidative stress, evidenced by the upregulation of antioxidant genes including catalase (p < 0.05), glutathione S-transferase (p < 0.05), and superoxide dismutase (p < 0.05). Despite some microbial communities exhibiting a temporary adaptive response, these mechanisms were insufficient to counteract the lethal effects of the herbicides. Our survival analysis showed a reduction in honeybee survival times, with paraquat having the most severe impact (p < 0.05). Additive or synergistic effects expected in the combined dose of paraquat and glyphosate herbicides did not significantly increase honeybee survival upon oral exposure (p > 0.05), suggesting a potential antagonistic interaction between the two compounds. This study underscores the urgent need for regionally specific environmental risk assessments and agricultural chemical management strategies that prioritize pollinator health. These findings call for comprehensive monitoring of pollinator health in agricultural ecosystems and investment in alternative pest management strategies to mitigate the profound and destabilizing effects of these herbicides on African honeybees
