Abstract: 【Aim】 As an important physiological signaling substance for photoperiodic signaling changes, melatonin is ubiquitous in living organisms and plays an important role in regulating the metabolic activities, immune activities, antiretroviral activities, and reproductive activities of living organisms. The objective of this research is to clarify the effects of different concentrations of exogenous melatonin on the growth, development and reproduction of Spodoptera frugiperda. 【Methods】 After S. frugiperda larvae hatched within 2 h were fed with artificial diets containing different concentrations (0, 0.02, 0.2, 2 and 20 μg/g) of exogenous melatonin by indoor feeding, the developmental duration, body size and weight changes, ovarian development progress, and adult longevity and fecundity changes of S. frugiperda were observed. 【Results】 When S. frugiperda larvae were fed with the artificial diets containing 0.2, 2 and 20 μg/g of exogenous melatonin, the 3rd-6th instar larval duration and total larval duration were significantly prolonged, and the female pupal duration was significantly shortened, as compared with those in the control (fed with the normal artificial diet). After exposure to 20 μg/g of exogenous melatonin, the total larval duration of S. frugiperda was the longest, prolonged by 2.53 d, as compared with that in the control, and the female pupal duration was the shortest, shortened by 1.67 d, as compared with that in the control. However, all concentrations of exogenous melatonin had no significant effect on the male pupal duration. After treatment with 2 and 20 μg/g of exogenous melatonin, the head capsule width of the 2nd-6th instar larvae reduced significantly, the larval body weight before prepupa and the female and male pupal weight decreased significantly, the adult longevity and oviposition period were significantly shortened, the average number of eggs laid per female and number of eggs laid per female per day were significantly decreased, as compared with those in the control. Under the treatment of 20 μg/g of exogenous melatonin, the average number of eggs laid per female and the number of eggs laid per female per day were the lowest, which decreased by 45.12% and 31.66%, respectively, as compared with those in the control. Anatomical observation of the reproductive system showed that the ovarian developmental rate of the female adults slowed down obviously with the increase of the concentration of exogenous melatonin. 【Conclusion】 Exogenous melatonin at high concentrations has obvious inhibitory effects on the growth, development and reproduction of S. frugiperda, resulting in prolonged developmental duration, decreased body size, body weight loss and decreased fecundity. The results of this study provide a theoretical basis for the potential utilization of melatonin in pest management and for the integrated control of S. frugiperda.

Key words: Spodoptera frugiperda, melatonin, growth and development, reproduction, ovary