A Stereoselective <i>CYP15A1</i> Epoxidase Mediates ( <i>10S</i> )-JH III Synthesis in a Parasitic Wasp <i>Scleroderma guani</i>

Juvenile hormone III (JH III) plays a central role in insect development and reproduction and has long been assumed to occur exclusively as the <i>R</i>-enantiomer. Here, we demonstrate that <i>Sclerodermus guani</i> exclusively synthesizes the <i>S</i>-enantiomer of JH III (<i>S</i>-JH III), as confirmed by electron circular dichroism (ECD) analysis and TD-DFT simulations. <i>S</i>-JH III is consistently present across developmental stages, peaking during the egg stage, and is also predominant in related species, suggesting taxon-specific stereoselectivity. In vitro and in vivo assays identified methyl farnesoate (MF) as the preferred precursor, with a strong bias toward <i>S</i>-JH III production. Enzymatic kinetics of purified SgCYP15A1 revealed significantly higher affinity and catalytic efficiency for <i>S</i>-JH III. Transcriptome analysis showed that <i>S</i>-JH III, but not <i>R</i>-JH III, upregulated genes involved in ovarian development and reproductive regulation. These findings uncover a highly stereoselective JH III biosynthetic pathway in <i>S. guani</i> and highlight its potential relevance to hymenopteran evolution and reproductive control. This finding not only expands current understanding of JH biosynthesis but also presents opportunities for developing stereoselective hormone analogs to enhance the behavioral efficacy of parasitoids in biological pest management.