Abstract: 【Aim】 Trapping by sex pheromone has been used as an effective tool to monitor and control the striped rice stem borer, Chilo suppressalis, an important rice pest. This study aims to clarify the mechanism of sex pheromone trapping and the mating status of trapped male moths of C. suppressalis. 【Methods】 The characteristics of internal genital organs of male adults of C. suppressalis at different age (day-old) and in different mating statuses were studied with behavioral bioassay and genital anatomy and compared with those of male adults captured with sex pheromone lure in the field. 【Results】 The primary segment of single ejaculatory duct of male moth of C. suppressalis could be divided into seven segments. The genital contents in the genital duct were mostly white and could be grouped into five grades (grade 0-4) according to the compactness, with two statuses of the genital duct fully and not fully filled with contents. With the increase of the age (day-old), the grades of genital contents in accessory glands and segments 3 and 4 of ejaculatory duct decreased. The proportion of unfulfilled duct in segments 5 and 7 and the grade of contents in segments 5 and 7 increased. The grades of contents in segments 5 and 7 and in the double ejaculatory duct were significantly lower in the newly mated male moths than those in the unmated individuals of the same age, while the grades of contents in segments 1-4 of the newly mated males were significantly higher than those of the unmated individuals within 1 h after mating. At 24 h after mating, there was no significant difference in the grade of contents between mated and unmated individuals. At 36 h after mating, the proportion of unfulfilled duct in segments 5 and 7 of the mated moths was higher than that of the unmated individuals. However, the response to sex pheromones did not significantly affect the contents in the genital duct. The grades of contents in the terminal half part of accessory gland of male moths trapped by sex pheromone from the field were significantly higher than those of the unmated moths of the 2-6-day-old, while these of segments 3 and 4 of male moths trapped by sex pheromone from the field significantly lower than those of the newly emerged (0-day-old) male moths. 【Conclusion】 The results show that the characteristics of genital contents can be used to distinguish the mated and unmated individuals of C. suppressalis within 12 h after mating. Sex pheromone trapping can attract a large number of 1-day-old unmated male moths and is an effective measure for the control of C. suppressalis. Our results lay a theoretical foundation for the determination of mating status of male moths of C. suppressalis and for pest monitoring and control by pheromone trapping.

Key words: Chilo suppressalis, male reproductive system, age, mating status, sex pheromone, mass trapping