Abstract: 【Aim】 This study aims to explore the effects of environmental factors such as photoperiod, sunset time and light intensity in the light-dark cycle on the circadian rhythm in oviposition of Grapholita molesta adults, and to provide a basis for developing control measures based on light interference with oviposition. 【Methods】 The circadian rhythm in oviposition of G. molesta adults was observed under natural light environment in the field in spring, summer and autumn, and the differences in oviposition rhythm were compared and analyzed under different photoperiods (15L∶9D, 14L∶10D and 13L∶11D), simulated sunset time (19:00 and 16:00) and different intensities (1 000, 500, 100, 50, 10, 5, 1, 0.5 and 0.1 mW/m²) of dim light interruption (1 h) in artificial climate chambers. 【Results】 G. molesta adults showed obvious oviposition rhythm under natural light environment in the field. In spring, summer and autumn (the sunset time was 18:30, 19:30 and 18:30, respectively), the oviposition peaks of G. molesta adults occurred at 18:00-19:00, 19:00-20:00 and 18:00-19:00, respectively, i. e., within 0.5 h before and after sunset. During this period, the light intensity changed dramatically, rapidly decreasing from 10 000 mW/m² to 0.01 mW/m2. There was no obvious difference in oviposition rhythm of G. molesta adults under different photoperiods (15L∶9D, 14L∶10D and 13L∶11D) at the same sunset time, showing a similar “unimodal” curve. When the simulated sunset time was 19:00 and 16:00, the oviposition rhythms of G. molesta adults were obviously different, and the oviposition peaks occurred at 19:00-20:00 and 16:00-17:00, respectively, i. e., 1 h after sunset, accounting for more than 54% of the daily total number of eggs laid. The oviposition rhythm of G. molesta adults changed under the dim light interruption environment before sunset. Compared with the “bimodal” curve with small front and large back under 1 000, 500 and 100 mW/m² of dim light interruption, the “bimodal” curve with large front and small back was observed in the oviposition rhythm of adults under 50, 10, 5, 1, 0.5 and 0.1 mW/m² of dim light interruption, with the oviposition peak occurring at 16:00-17:00 (i. e., during the dim light interruption period)(more than 40% of oviposition percentage), followed by that at 19:00-20:00. There were significant differences in the daily numbers of eggs laid per female under different intensities of dim light interruption, with the highest daily numbers of eggs laid per female (33.05 and 31.00 grains, respectively) under 0.5 and 0.1 mW/m² of dim light interruption， respectively.【Conclusion】Light-dark cycle and light intensity can affect the circadian rhythm in oviposition of G. molesta adults, and oviposition activities mainly occur in dim light (below 50 mW/m²) or darkness.

Key words: Grapholita molesta, oviposition, circadian rhythm, light-dark cycle, sunset time, light intensity