Silencing of fatty acid synthase disrupts lipid metabolism, reducing diapause induction and reproductive output in <i>Trichogramma dendrolimi</i> (Hymenoptera: Trichogrammatidae) without affecting female longevity

Fatty acid synthase (FAS) plays a central role in lipid metabolism, influencing critical physiological processes such as reproduction and diapause in insects. In this study, we investigated the function of FAS in Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae), a key egg parasitoid used in biological pest control. Using RNA interference (RNAi), we achieved significant knockdown of FAS expression (>60%), which led to a 28.4% reduction in diapause proportion and a 37.5% decrease in parasitization rates compared to controls. FAS silencing also reduced ovarian egg load by 33.2% and mature egg proportion by 41.7%, demonstrating its essential role in oocyte maturation. Notably, vitellogenin receptor (VgR) expression was dramatically suppressed (84.3%) following FAS knockdown, suggesting a regulatory link between lipid metabolism and yolk precursor uptake, despite the absence of canonical vitellogenin in T. dendrolimi. Intriguingly, while FAS knockdown impaired reproductive output, adult longevity remained unaffected, indicating a decoupling of fecundity and lifespan trade-offs in this species. Additionally, transgenerational effects were observed, with offspring emergence rates declining by 28.4% in the F2 generation. Our findings establish FAS as a master regulator of reproduction in T. dendrolimi, mediating lipid allocation, diapause plasticity, and vitellogenic efficiency. These results provide novel insights into the metabolic adaptations underlying enhanced reproductive fitness in parasitic wasps and have implications for optimizing mass-rearing protocols in biological control programs.