Toxic Synergies: a Systematic Review and Meta-analysis of the Combined Effects of Pesticide Mixtures on Apis mellifera in Arid Environments

Background Honey bees play a pivotal role in global agriculture through pollination, yet their populations are increasingly threatened by exposure to complex mixtures of pesticides. While individual pesticide toxicity has been widely studied, limited attention has been given to the synergistic or antagonistic effects of pesticide combinations. Objective This systematic review and meta-analysis aimed to evaluate the acute and sub-lethal effects of pesticide mixtures on Apis mellifera , with a particular focus on mortality, learning and memory impairment, and residue accumulation in hive products. Methods The PRISMA framework guided a comprehensive literature search across databases, resulting in 543 identified records. After screening and eligibility assessment, six studies were included in the final review. Data were extracted on pesticide types, concentrations, exposure routes, bee species, and outcome measures. Effect size metrics such as LC₅₀, LD₅₀, and Mixture Dose Ratio (MDR) were used. A forest plot was generated based on calculated risk ratios. Results Most included studies reported synergistic or additive interactions between pesticide components, with MDR values ranging from 3.6 to 5.3. Laboratory studies demonstrated that combinations of neonicotinoids and pyrethroids significantly increased bee mortality and impaired cognitive functions. Field-based studies confirmed the accumulation of pesticide residues in bee tissues and hive products. The pooled data revealed a consistent trend of increased health risk to honey bees from pesticide mixtures compared to individual compounds. Conclusion The review highlights the underestimated threat posed by pesticide mixtures to honey bee populations. The evidence underscores the urgent need for regulatory frameworks to consider mixture toxicity in environmental risk assessments. Future studies should incorporate chronic exposure assessments and field-level validations to better reflect real-world scenarios.