Abstract: 【Aim】 This study aims to clarify the effects of exogenous juvenile hormone (JH) on the ovarian development and transcriptional levels of the key genes in the reproduction-related signaling pathways of Harmonia axyridis. 【Methods】 The 2-day-old female adults of H. axyridis fed with artificial diet were exposed to different doses (80, 120 and 160 ng/individual) of JHⅢ by topical application method for 1, 3, 5, 7 and 9 d (the female adults fed with the turnip aphid, Lipaphis erysimi, were used as the blank control group, and those treated with acetone solution of the same volume by topical application method as the vehicle control group), the ovaries were dissected, and the ovarian length and the length and width of their first egg chamber were photographed and measured. qPCR was used to analyze the expression levels of the key genes including JH receptor methoprene-tolerant (Met) gene, krüppel homolog 1 (Kr-h1) gene, vitellogenin genes (Vg1 and Vg2) and vitellogenin receptor (VgR) gene in the reproduction-related signal pathways of the female adults of H. axyridis exposed to the optimum dose (120 ng/individual) of JHⅢ for 1, 5, and 9 d. 【Results】 Compared with the vehicle control group, treatments with 80 and 120 ng/individual of JHⅢ by topical application method could promote the ovarian 
development of H. axyridis adults. After the 2-day-old female adults were exposed to 120 ng/individual of JHⅢ for 7 d, a large amount of yolk deposition appeared in the ovary, which was consistent with the ovarian developmental state in the blank control group fed 
with the turnip aphid, and the ovarian length and the length and width of the first egg chamber were significantly higher than those in the vehicle control group. However, the treatment with 160 ng/individual of JHⅢ inhibited the ovarian development of H. axyridis adults. The qPCR results showed that the expression levels of HaMet, HaKr-h1, HaVg1, HaVg2 and HaVgR in female adults at 5 and 9 d after treatment with 120 ng/individual of JHⅢ increased as compared to the those in the control group (acetone treatment group): those of HaMet, HaVg1 and HaVgR in female adults at 5 d after treatment were 2.78, 13.14 and 8.28 times, respectively, and those in female adults at 9 d after treatment were 2.36, 1.85, and 2.01 times, respectively, as high as those in the control group, showing extremely significant difference. 【Conclusion】 JHⅢ at the dose of 120 ng/individual can promote the ovarian development of H. axyridis adults and upregulate the expression levels of HaMet, HaKr-h1, HaVg and HaVgR in female adults at 5 and 9 d after treatment. It is speculated that these key genes play important roles in the regulation of JH on the ovarian development and yolk formation of H. axyridis.

Key words: Harmonia axyridis, exogenous juvenile hormone, ovarian development, signaling pathway, key genes