Short-term ecotoxicogenomic responses reveal early molecular mechanisms of pyraclostrobin toxicity in honey bees

Bees are essential to biodiversity and food production but are increasingly exposed to agricultural fungicides, such as pyraclostrobin (PYR), which is frequently detected in hive matrices. This study determined the oral lethal dose (LD₅₀) of PYR in Africanized Apis mellifera and evaluated early transcriptomic responses in forager bees following one and four-hour exposure to contaminated syrup. Head tissues were subjected to RNA sequencing. The LD₅₀ was 8.85μg/bee, and a sublethal dose was selected for molecular analyses. After one hour, 432 genes were differentially expressed, with 104 shared between lethal and sublethal treatments. Upregulated genes were mainly associated with detoxification and immune pathways, indicating activation of xenobiotic processing and stress defence mechanisms. No significant transcriptional changes were observed after four hours. These findings demonstrate rapid molecular responses to PYR exposure and highlight the value of ecotoxicogenomics for detecting sublethal pesticide effects and informing risk assessment for pollinators.