Validamycin Inhibits the Reproductive Capacity of Spodoptera frugiperda (Lepidoptera: Noctuidae) by Suppressing the Activity of Trehalase

Spodoptera frugiperda (J. E. Smith, 1797), an omnivorous crop pest worldwide, reproduces prolifically. Validamycin, a competitive natural inhibitor of trehalase, is regarded as an effective and safe insecticide. Pupae were injected with a validamycin gradient (0.5–10 µg/µL) to block trehalase; enzyme activity and the Vitellogenin gene (Vg)/its receptor gene (VgR) expression (rpL10 reference) were subsequently quantified to determine the compound’s impact on S. frugiperda ontogeny and fecundity. Validamycin directly inhibited pupal membrane-bound trehalase, sharply lowering glycogen. Both pupal and adult mortality rose with dose, yielding marked abnormalities versus the Control Check (CK) group. At 0.5 μg/μL validamycin, eggs blackened and clumped in the lateral oviduct, blocking release; treated females produced far fewer eggs by day 4, exhibited ovarian atrophy, shorter lifespan, and low hatchability. The expression levels of Vg and VgR in the ovaries of the fall armyworm were consistent with the changes in the ovarian developmental phenotype. Validamycin significantly inhibited the activity of trehalase in S. frugiperda, severely hindering their normal eclosion and lowering the potential reproductive capacity of S. frugiperda. Simultaneously, it directly affects ovarian development and the lifespan of female moths. The results provide data to support the development of new methods for controlling S. frugiperda.