Screening and Synergistic Effects of Phenoloxidase Inhibitors in Spodoptera litura

. Bioassays showed that 18 candidate compounds enhanced λ-cyhalothrin toxicity to varying degrees. AG690 (PubChem CID: 3119969) showed the strongest synergistic effect, with synergistic ratios of 1.73, 1.82, and 1.64 at 24, 48, and 72 h, respectively. AG690 reduced PO expression and PO enzymatic activity by 65.79% and 52.41%, respectively, and suppressed cellular immune responses as well as SOD, POD, and lysozyme activities. These findings support PO-targeted immune suppression as a strategy for developing insecticide synergists.