Optimizing Sex Ratio and Colony Size to Enhance Reproduction and Mass-Rearing in Spodoptera litura Under Controlled...

The tobacco cutworm Spodoptera litura is a globally distributed polyphagous agricultural pest and common factitious host for mass-producing biological control agents (e.g., predators, parasitoids, entomopathogens), owing to its rapid development, and high reproductive capacity. Efficient large scale rearing of S. litura is also fundamental for developing sterile insect techniques (SIT) application, which require stable, high quality insect colonies to ensure consistent sterilization outcomes and effective field release strategies. However, skewed sex ratios frequently constrain colony performance and limit the efficiency of large-scale rearing systems. In this study, seven sex ratio treatments (1:1, 3:2, 2:1, 5:2, 3:1, 7:2, 4:1) were established to quantify key reproductive traits. Among the initial ratios, 1:1 produced the highest female longevity and maximum fecundity per female. This optimal ratio was subsequently scaled to colony sizes of 20:20, 40:40, and 60:60 to evaluate proportional effects on reproductive output. Fecundity per female was highest at the 1:1 sex ratio and decreased with increasing population size. The 40:40 configuration yielded the best overall reproductive performance. These findings refine the understanding of sex ratio dependent reproductive dynamics in S. litura and provide practical guidance for improving mass-rearing efficiency both for factitious host production and for supporting SIT development.