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

## TL;DR

Adding catalpol to the diet of Harmonia axyridis improves its growth, reproduction, and energy metabolism, aiding in green pest control.

## Contribution

Catalpol is first used in H. axyridis diets to enhance development and reproduction through metabolic regulation.

## Key findings

- Catalpol shortened larval and pupal stages and increased pupal weight in H. axyridis.
- Catalpol improved reproductive capacity by upregulating vitellogenin genes and enhancing hatching rates.
- Catalpol boosted energy metabolism by increasing glycogen and glucose levels and trehalase gene expression.

## Abstract

The large-scale reproduction of natural enemy insects is the prerequisite for achieving green control, and the development of artificial diets is the key to the expansion of natural enemy populations. This study investigated the growth and development, reproductive capacity, and energy metabolism levels of Harmonia axyridis under different feeding conditions and found that artificial diets supplemented with catalpol significantly promoted various physiological indicators of H. axyridis, indicating that catalpol has the potential to improve artificial diets for natural enemy insects and can be used in the industrialized cultivation of natural enemy insects and pest control.

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 Harmonia axyridis, aiming to comprehensively assess the effects of such dietary regimens on larval development, reproductive performance, and the regulation of energy metabolism in H. axyridis. 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 Vg1 and Vg2 and their receptor gene VgR 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 TRE2 was significantly higher than that in the control group, and the expression level of the soluble trehalase enzyme gene TRE1 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 H. axyridis 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.