Abstract: 【Aim】The objective of this research is to explore the effects of DOPA decarboxylase (DDC) on fecundity in the multicolored Asian beetle, Harmonia axyridis, and its regulatory mechanism. 【Methods】RNA interference (RNAi) was used to suppress the expression of DDC gene (HaDDC) in the 4th instar larvae of H. axyridis, and the cumulative number of eggs laid in 20 d was counted from the 8th day after adult emergence and the egg hatching rate of offspring was recorded on the 3rd day after egg laying. Then the ovaries of female adults of H. axyridis were dissected, the ovarian tissue morphology and the number of ovarioles of the 8-day-old adults between the treatment group (injected with dsHaDDC) and the control group (injected with dsGFP), and the development of eggs in the ovarioles of the 14- and 20-day-old adults between the treatment group and the control group were observed and recorded.【Results】After the expression of HaDDC gene of both sexes of H. axyridis was inhibited by RNAi, the cumulative number of eggs laid by adults in 20 d was 38.67±7.80, which was significantly lower than that of the control group (371.33±84.31). After the expression of HaDDC gene in female and male adults was inhibited, the cumulative numbers of eggs laid in 20 d were 135.50±28.38 and 76.00±14.00, respectively, which were significantly different from that of the control group. The egg hatching rate of offspring was 0 when the expression of HaDDC gene in both sexes was inhibited. On the 8th day after emergence of H. axyridis, the ovarian tissue morphology and the number of ovarioles in the treatment group were not significantly different from the control. On the 14th day after adult emergence, the ovaries of H. axyridis were plump, and the oocytes were developed in the bilateral ovarioles. However, compared with the control group, no mature eggs were found in the treatment group.【Conclusion】Based on the above results, we can preliminarily conclude that DDC can regulate the fecundity of H. axyridis by participating in the development process from oocyte to mature eggs.

Key words: Harmonia axyridis, dopamine, DOPA decarboxylase, RNAi, fecundity