Abstract: To clarify the effects of different concentrations of exogenous melatonin on the biological characteristic of Aphis craccivora, we measured the developmental and reproductive indices of A. craccivora under different concentrations of exogenous melatonin by plant meditation in vitro. The results showed that feeding exogenous melatonin had a significant effect on the developmental duration, body size, fecundity and life-table parameters of A. craccivora, which was dose-dependent. With the increases of exogenous melatonin concentrations, the developmental duration of alfalfa aphid was significantly prolonged, the growth rate slowed down and the body size decreased. Meanwhile, the adult longevity and reproductive period were shortened gradually. The average fecundity and the average daily fecundity per female were decreased, and the number of embryos in ovariole tubes was decreased compared with the control. Under the high concentration (50 mg·L^-1) treatment, A. craccivora had the longest developmental duration (11.14 d), the shortest adult longevity (19.85 d) and reproductive period (14.71 d). Body length (1.48 mm), hind food tibia length (0.77 mm), and body weight (0.63 mg) were the lowest. Furthermore, A. craccivora had the lowest average fecundity of per female (66.14 offsprings per female) because of the decreased number of embryos per ovariole in ovaries of A. craccivora. Our results suggested that feeding melatonin has a signi-ficant effect on the growth and reproduction of A. craccivora.

Key words: Aphis craccivora, exogenous melatonin, developmental duration, body size,  reproduction, ovary.