Abstract: 【Aim】The purpose of this study is to clarify the changes in the titer of juvenile hormone (JH) JHⅢ and the expression levels of its metabolism-related genes in different developmental stages and during phase transition of Oedaleus asiaticus, so as to lay a foundation for elucidating the physiological function of JH in regulating the phase transition of O. asiaticus.【Methods】High performance liquid chromatography was used to determine the titer change of juvenile hormone JHⅢ in the haemolymph of O. asiaticus of solitarious and gregarious phases at different developmental stages (the 4th and 5th instar nymphs, and 1-, 4-, 7-, 10-, 13- and 20-day-old adults) and at 1, 3, 5 and 7 d after the 3rd instar nymphs of O. asiaticus were subjected to gregarilization treatment. The expression levels of three kinds of genes related to juvenile hormone metabolism, i.e, juvenile hormone esterase (JHE) gene, juvenile hormone methyltransferase (JHAMT) gene and juvenile hormone epoxide hydrolase (JHEH) gene at 1, 3, 5 and 7 d after the 3rd instar nymphs of O. asiaticus were subjected to gregarilization treatment were determined by qRT-PCR. The phase transition rate of O. asiaticus was determined after the 3rd instar nymphs were subjected to JHⅢ liquid immersion and gregarilization treatment.【Results】The JHⅢ titer in the hemolymph of O. asiaticus was very low, with the maximum titers below 50 ng/mL in the 4th and 5th instar nymphs of the two phases and the maximum titers below 100 ng/mL in adults of the two phases. The JHⅢ titer increased with the increase of the adult day-old age, and reached a peak at the 13-day-old, and then decreased slowly with the increase of the day-old age, showing a similar trend in female and male adults of the both two phases. The JHⅢ titers in the haemolymph of various day-old adults of solitarious phase except for the 1-day-old adults were significantly higher than those of gregarious phase of O. asiaticus. The JHⅢ titers in the haemolymph of O. asiaticus at 1-7 d after the 3rd instar nymphs were subjected to gregarilization treatment significantly decreased in vivo as compared to those in the corresponding controls (solitarious phase). The expression levels of JHE, JHAMT and JHEH genes changed significantly during the phase transition and showed a trend of first increase and then decrease. The increase of JHⅢ concentration could effectively inhibit the transition of O. asiaticus from the solitarious phase to the gregarious phase.【Conclusion】The juvenile hormone JHⅢ plays an important role in the phase transition of O. asiaticus. JHE, JHAMT and JHEH genes may play different functions in the process of phase transition of O. asiaticus.

Key words: Oedaleus asiaticus; juvenile hormone, gene expression, solitarious phase, gregarious phase, phase transition