Abstract: 【Aim】Picoxystrobin is a fungicide that honey bees are often exposed to, but its effect on the health of worker bees was often neglected. This study aims to investigate the effects of picoxystrobin stress on different day-old worker bees of Apis mellifera ligustica, and provide a theoretical basis for bee health breeding and pollination safety. 【Methods】The 1-, 8- and 21-day-old A. mellifera ligustica workers were continuously exposed to field-recommended concentrations (113, 150, 225 and 281 mg/L) of picoxystrobin for 7 d, the survival rates of different day-old worker bees in each concentration treatment group were documented, and the activities of the protective enzymes superoxide dismutase (SOD) and catalase (CAT), and the detoxification enzymes carboxylesterase (CarE), glutathione S-transferase (GST) and cytochrome P450 monooxygenase (CYP450) in worker bees were examined. The expression levels of nutrition-related genes insulin-like peptide genes (ILP1 and ILP2) and Vitellogenin gene, and immune-related genes (Abaecin gene, Apidaecin gene, Defensin1 gene, Hymenoptaecin gene) were detected by RT-qPCR. 【Results】 Continuous exposure to 113, 150, 225 and 281 mg/L picoxystrobin significantly reduced the survival rates of the 1- and 21-day-old worker bees of A. mellifera ligustica compared with the control group. In 113, 150 and 225 mg/L picoxystrobin treatment groups, the activities of CAT and CYP450 in the 1- and 8-day-old worker bees were increased, while the activities of SOD, CarE and GST decreased with the increasing treatment concentration as compared with those in the control group. In the 21-day-old worker bees, picoxystrobin induced the activities of CAT, SOD and GST, but inhibited the CarE activity compared with the control group. The expression levels of ILP1 and ILP2 in the 1- and 21-day-old worker bees treated with picoxystrobin were downregulated compared with those in the control group. In contrast, the expression levels of Vitellogenin in the 1- and 8-day-old worker bees treated with picoxystrobin were higher than those in the control group. Pyraclostrobin significantly increased the expression levels of Apidaecin and Hymenoptaecin in the 1-day-old worker bees, but inhibited the expression levels of Apidaecin and Hymenoptaecin in the 8-day-old worker bees compared with the control group. At the same time, 225 and 281 mg/L pyraclostrobin significantly inhibited the expression levels of Abaecin, Apidaecin, Defensin1 and Hymenoptaecin in the 21-day-old worker bees compared with the control group. 【Conclusion】 The field-recommended concentrations of pyraclostrobin have significant toxicity to A. mellifera ligustica workers of different day-olds, causing impacts on their survival, enzyme activities, nutritional metabolism, and immune ability, thereby increasing their survival pressure and threatening the health of the colony.

Key words: Apis mellifera ligustica, worker bees, picoxystrobin, survival rate, enzyme activity, nutrition, immunity