Combined pesticide residues and biomarker responses in honey bees ( <i>Apis mellifera</i> ) under realistic field exposure in agricultural landscapes

Honey bees (Apis mellifera) are frequently exposed to complex pesticide mixtures in agricultural landscapes. This field-based study evaluated the presence of both experimentally applied and landscape-derived pesticides in honey bees foraging in a soybean field in Entre Ríos Province, Argentina, and assessed their effects on key biochemical biomarkers. A total of 45 foragers were collected before, during, and after the application of lambda-cyhalothrin, methoxyfenozide, and glyphosate. N = 15 were analyzed for pesticide residues (pre-and post- application: n = 6; during: n = 3), while enzymatic biomarkers were determined in 30 individuals (pre- and post- application: n = 12; during: n = 6). Regarding residues, methoxyfenozide was detected only during application (max. 50 µg kg−1), whereas glyphosate was detected at the three periods, peaking during application (146 µg kg−1). The aminomethylphosphonic acid occurred in 100% of samples across the three studied periods in the range of 27–47 µg kg−1. Lambda-cyhalothrin remained mostly below quantification limits in the three periods. Unexpectedly, several pesticides not applied in the experiment—including 2,4-D, atrazine, imidacloprid, and tebuconazole—were found in 20–40% of total samples, indicating contamination from the broader landscape. Regarding biomarker responses, carboxylesterase activity increased during (+370%) and post-application (+256%), and glutathione S-transferase rose during application (+46%). These findings demonstrate that even under good agricultural practices, honey bees experience simultaneous exposure to multiple agrochemicals that activate detoxification pathways. The integration of multiresidue pesticide profiling with biochemical biomarker responses constitutes a sensitive and ecologically relevant approach for pollinator health assessment under field-realistic exposure scenarios for pesticide monitoring and sustainable management strategies in intensive agricultural regions.