Functional characterization of fatty acid synthase gene ( <i>FAS</i> ) in the reproduction of mirid predator, <i>Cyrtorhinus lividipennis</i> (Hemiptera: Miridae)

Natural enemies serve a crucial role in crop protection through the regulation of pest population dynamics. <i>Cyrtorhinus lividipennis</i> is an important natural enemy of rice planthoppers. Fatty acid synthase (FAS), a multifunctional enzyme crucial for fatty acid biosynthesis, serves as a vital energy source for insect reproduction. However, the function of FAS in the reproductive processes of <i>C. lividipennis</i> remains incompletely understood. In this study, the <i>ClFAS</i> gene was successfully cloned from <i>C. lividipennis</i>. The open reading frame of <i>ClFAS</i> was 7224 bp, encoding a putative protein of 2407 amino acids. The expression levels of <i>ClFAS</i> were notably elevated in the fifth-instar nymphs, adults, as well as in the fat body and ovaries of female individuals. Silencing of <i>ClFAS</i> resulted in a reduction of 58.4%, 34.6%, and 49.0% in the expression levels of <i>ClVg</i> at 1-, 2-, and 3-days post-dsRNA injection, respectively. Furthermore, RNA interference (RNAi)-mediated depletion of <i>ClFAS</i> not only suppressed the Vg protein expression but also significantly impaired oocyte maturation and ovarian development. The fecundity of dsFAS-treated <i>C. lividipennis</i> females was markedly reduced by 49.5%, accompanied by significant decreases of 32.7% in oviposition duration and 26.3% in female adult lifespan. Our findings showed that ClFAS positively regulates the reproduction of <i>C. lividipennis</i> by promoting vitellogenesis and ovarian development, which provides valuable insights into how lipid metabolism governs fecundity in predatory insects.