Supplemental Sugar Is Required for Sex Pheromone Biosynthesis in Mythimna separata

Supplemental nutrients of adult moths maximize moth fitness and contribute to the pollination of many plants. Previous reports have revealed that sugar feeding promotes to sex pheromone biosynthesis by increasing the haemolymph trehalose concentration in mating moths. Here, Mythimna separata adults were employed as a model to investigate the effect of sugar feeding on sex pheromone biosynthesis. Results showed that in virgin females, sugar feeding markedly increased the concentrations of trehalose, pyruvic acid, and acyl-CoA in pheromone glands (PGs), which in turn led to an increase in sex pheromone titer, female ability to attract males and successfully mating frequency in sugar-fed females. Consistently, sugar-fed females laid more eggs than water-fed females. Furthermore, the refeeding of starved females also caused significantly increase in the concentrations of trehalose, pyruvic acid, and acyl-CoA in PGs, thus facilitating a significant increase in sex pheromone production. Most importantly, RNAi-mediated knockdown of trehalase (leading to PG starvation) resulted in an increase in trehalose content, and decrease in the concentrations of pyruvic acid, and acyl-CoA in PGs, which in turn led to a decrease of sex pheromone titer, female ability to attract males and successful mating efficacy. Altogether, results revealed a mechanism by which sugar feeding contributed to trehalose utilization in PGs, promoted to significantly increased sex pheromone precursor by increasing the concentrations of pyruvic acid and acyl-CoA, and facilitated to sex pheromone biosynthesis and successful mating.

Male accessory gland factors increased sex pheromone titres in the glands of Spodoptera litura female moths by inhibiting calling behavior

Moths are the most widely studied example of pheromones in animals. However, little is known about the mechanism of intrasexual and mating-related intersexual regulation of pheromone production and release in female moths. Our previous studies in Spodoptera litura found that mating induced a higher sex pheromone titre in the pheromone gland (PG) and mating or male accessory gland (MAG) extract suppressed female calling behavior. We therefore hypothesize that the inhibition of female calling behavior by mating or MAG factors likely suppresses the release of sex pheromones and thus results in a higher pheromone titre in the PG. To test this hypothesis, in the present study, we introduced an artificial calling behavior suppression treatment by gently knocking on and shaking the testing boxes contained moths once every 10 minutes. Results show that this treatment significantly increased pheromone titres in virgin or saline injected virgin females, and the increase rates are similar to those of mating and MAG extract treated ones. These results have suggested that the increase of sex pheromone titer in the female PG after mating in S. litura is due to the inhibition of female calling behavior by MAG factors. Moreover, results of this study also suggest that female calling behavior is positively correlated to pheromone release and likewise, the calling behavior and sex pheromone release in S. litura females are directly under the neural control, and modulated by molecular and environmental factors.