Abstract: 【Aim】To explore the main mate selection strategies and their relationship with the fecundity in the fall armyworm, Spodoptera frugiperda, and to explore the evolutionary significance and mechanism of mate selection strategies based on the theory of sexual selection.【Methods】Marked female and male adults of S. frugiperda with different day-old ages, body weight and mating experiences were paired, and their mate selections were observed, the morphological characteristics (body length, antennal length, wing length, and thoracic and abdominal length and width) and fecundity (number of eggs laid per female, egg hatching rate and number of hatched larvae) of mated and unmated female and male adults were measured and compared. 【Results】Both female and male adults of S. frugiperda preferred to mate with young, heavy and unmated adults. The probability of female adults selecting young (3-day-old) male adults to mate (65.45%) was significantly higher than that selecting old (7-day-old) male adults to mate (34.55%), and the probability of male adults selecting 3-day-old female adults to mate (82.35%) was significantly higher than that selecting 7-day-old female adults to mate(17.65%). The probability of female adults selecting heavy male adults to mate (74.58%) was significantly higher than that selecting light males to mate (25.42%), and the probability of male adults selecting heavy female adults to mate (66.67%) was significantly higher than that selecting light females to mate (33.33%). The probability of female adults selecting male adults without mating experience to mate (64.91%) was significantly higher than that selecting males with mating experience to mate (35.09%), and the probability of male adults selecting female adults without mating experience to mate (78.57%) was significantly higher than that selecting females with mating experience to mate (21.43%). The body length, antennal length and wing length of male adults who obtained mating rights were significantly greater than those of males who did not obtain mating rights, while the body length, wing length, and abdominal length and width of female adults who obtained mating rights were significantly greater than those of females who did not obtain mating rights. Fecundity studies showed that compared to the female adults who chose to mate with male adults with mating experience, female adults who chose to mate with male adults without mating experience could achieve higher number of eggs laid per female (unmated vs mated: 1 024 grains  vs 917 grains) and egg hatching rate (unmated vs mated: 91.36% vs 89.10%). Compared to old and light female adults chosen by male adults to mate, young and heavy female adults chosen by male adults to mate had higher number of eggs laid per female (young vs old: 1 001 grains vs 939 grains; heavy vs: light: 1 039 grains vs 830 grains) and number of hatched larvae (young vs old: 917 vs 838; heavy vs light: 950 vs 754). The age and body weight of male adults had no significant effects on the fecundity of female adults. 【Conclusion】 Both female and male adults of S. frugiperda have mate selection preferences related to morphological and physiological traits. Female and male adults can obtain material benefits (more offspring) to different degrees through mate selection, thus contributing to the reproduction and evolution of the species. This study contributes to the study of insect reproductive behavior and sexual selection mechanism, and to the exploration of pest control strategies based on reproductive behavior.

Key words: Spodoptera frugiperda, mate selection, fecundity, sexual selection, pest control