Abstract: 【Aim】 The increasing popularization of the application of sex pheromone trapping in the monitoring and control of the rice leaf roller, Cnaphalocrocis medinalis, has also increased the necessity to distinguish the developmental status of the internal reproductive system of the trapped male adults, which, in turn, has been essential to obtaining the key forecasting indexes and evaluating the control effects by sex pheromone trapping. This study aims to obtain the morphological indicators of the developmental status of the male internal reproductive system of C. medinalis adults, and furthermore to distinguish the population developmental status on the basis of the age composition of the trapped males for sex pheromone forecasting. 【Methods】 At different days post eclosion from the laboratory-cultured pupae, different organs of the male internal reproductive system of C. medinalis adults were dissected and measured under the microscope. A standard based on the half length of testis was developed and used to distinguish the age of male adults daily collected in sex pheromone traps. The speculated age composition of the trapped males was then used to postulate the population dynamics of the insect. 【Results】 After comparing the morphology of testes, seminal vesicle, vas deferens, accessory gland and ejaculatory ducts, we found that the half length of testis reduced stably and was negatively correlated with the age in days of the cultured male adults. The semi-major axis length of testes of the male adults at the 8th day post eclosion was averagely reduced by 41.55% as compared with that in males at the 1st day post eclosion. The field data in 2015 and 2016 both showed two peaks, representing respectively the occurrence of the 1 and 4 day-old male adults, in the age composition curve of the males trapped by sex pheromones. According to the speculated age composition of the daily collected male adults in sex pheromone traps in Meishan in 2015 and Zigong in 2016 in Sichuan, respectively, the emergence dynamics of the 1 day-old male adults could be postulated, which were found to be in coincidence to the data of field investigation. 【Conclusion】 The changes in the testis size of C. medinalis could reflect the age of its male adults. The investigation of the testis size and the consequently obtained age composition of the males could help the forecasting of the population dynamics of this pest.

Key words: Cnaphalocrocis medinalis, male internal reproductive system, developmental status, morphological indicators, population dynamics, sex pheromone trapping