Role of Dietary Catalpol Supplementation in Regulating Reproductive Development of Harmonia axyridis

The mass rearing of natural enemy insects is a cornerstone of effective green pest control, making the development of optimized artificial diets critical for sustaining large populations. However, existing artificial diets often have limitations, including inhibitory effects on the reproductive development of natural enemies. In this study, we innovatively incorporated 20% catalpol into the artificial diets for <i>Harmonia axyridis</i>, aiming to comprehensively assess the effects of such dietary regimens on larval development, reproductive performance, and the regulation of energy metabolism in <i>H. axyridis</i>. Our results demonstrated that catalpol supplementation significantly shortened the duration of the 4th instar larval and pupal stages and increased pupal weight. Furthermore, catalpol treatment enhanced reproductive capacity, as evidenced by increased fecundity, improved hatching rate stability, and enhanced ovarian development. This effect was directly correlated with the significant upregulation of the vitellogenin genes <i>Vg1</i> and <i>Vg2</i> and their receptor gene <i>VgR</i> at 3 days post-emergence. Regarding energy metabolism, catalpol supplementation led to increased glycogen reserves and glucose content. The expression of the membrane-bound trehalase enzyme gene <i>TRE2</i> was significantly higher than that in the control group, and the expression level of the soluble trehalase enzyme gene <i>TRE1</i> also showed a significant increase. These findings indicate that catalpol effectively optimized energy metabolism, thereby accelerating developmental processes and enhancing reproductive capacity. In this study, we elucidated the mechanism by which catalpol regulates physiological metabolism in predatory natural enemy insects. For the first time, catalpol was incorporated into the artificial diet of <i>H. axyridis</i> as a synergistic component, significantly enhancing its growth, reproductive capacity, and energy metabolism. These findings provide a scientific basis for developing efficient artificial feeding systems and improving the field adaptability of natural enemy insects.