Insecticide Susceptibility and Detoxifying Enzyme Activity in Managed Honey Bees in a Southern Mexico Landscape

Pesticide exposure in honey bees triggers a series of biochemical cascades, including the activation of detoxifying enzymes. Consequently, a specific pesticide susceptibility profile may correlate with a distinct enzymatic activity pattern. In this study, we analyzed pesticide residues in honey samples through gas chromatography, assessed the susceptibility profile by determining the median Lethal Time (LT₅₀ for commercial formulations of malathion, imidacloprid, and cypermethrin, and measured the activity of detoxifying enzymes - ρNPA, α- and β-esterases P₄₅₀, GST, and AChE - in foragers from thirteen apiaries located in Chiapas, Mexico. We also conducted palynological analyses to identify pollen from crops in the bees’ diets to corroborate the pesticide residue findings. No pesticide residues were detected above the method's detection limits in our samples; palynological analysis showed that foragers primarily collected pollen from wild plant species, suggesting low probability of exposure to insecticides and supporting the pesticide residues results. The malathion formulation caused the highest toxicity (lowest LT₅₀) across all sites, whereas cypermethrin was the least toxic (mortality < 20% at 12 h after exposure). Enzyme activities varied across study sites: foragers from the Tapachula apiary exhibited the lowest AChE activity, whereas those from Villa Comaltitlan showed the highest activity. No clear correlation between enzyme activity and LT₅₀ for the different formulations was observed. Our results suggest that managed honey bee apiaries were exposed to xenobiotics other than insecticides, as shown by residue and palynological analyses, leading to distinct enzymatic and susceptibility profiles.