Abstract: 【Aim】 The effectiveness of controlling and monitoring the striped rice stem borer, Chilo suppressalis, by pheromone trapping had been verified in the field. However, since the male moth can mate multiple times, the mass trapping control strategy of C. suppressalis has been in debate for decades. The purpose of this study is to explore the mating frequency of male moths of C. suppressalis and its effect on the fecundity of female moths, and to understand the mechanism of pest control by pheromone mass trapping. 【Methods】 The mating frequency and duration of mating of male moths of C. suppressalis paired in different female to male ratios (1∶1, 4∶1 and 10∶10) were investigated by behavioral methods. The effects of mating frequency on the size of testis, bursa copulatrix and spermatophore and the number of eggs laid by female moths were observed and analyzed by behavioural and anatomical methods. 【Results】 When the female and male moths were paired in the 1∶1 ratio, the proportions of male moths mating at least once and mating multiple times were 74.0% and 36.0%, respectively, and the average mating frequency of male moths was 1.7 times. The first mating was always found in the male at the 0-1-day-old. Most of the male moths mating multiple times were firstly mated at the 0-1-day-old. When the female and male moths were paired in the 4∶1 ratio, the proportions of male moths mating at least once and multiple times were 69.4% and 51.3%, respectively, and the average mating frequency was 2.1 times, which was significantly higher than that of male moths paired with females in the 1∶1 ratio. When the female and male moths were paired in the 10∶10 ratio, the proportions of male moths mating at least once and multiple times were 65.5% and 37.8%, respectively, and the average mating frequency was 1.9 times. The duration of the 3rd mating of males was significantly longer than that of the 1st and the 2nd mating, but there was no significant difference in the testicular volume among males mating once, twice and thrice. There was no significant difference in the volume of bursa copulatrix and spermatophore of female and in the number of eggs laid per female, which mated with males at different mating frequencies. 【Conclusion】 Only a portion of C. suppressalis male moths can mate multiple times and their first mating mainly occurred at the 0-1-day-old. A significant number of male moths do not mate in their life. Our results provide a theoretical basis for controlling C. suppressalis with pheromone trapping.

Key words: Chilo suppressalis, multiple mating, testis, bursa copulatrix, spermatophore, oviposition amount, mating duration