Analysis of the Effects of Appressorium Formation on Insect Cuticle Metabolism Based on LC-MS.

The appressorium is a specialised infection structure formed by during host invasion. This study used sulforaphane to regulate the formation rate of , evaluated the correlation between appressorium formation and fungal pathogenicity, and explored its impact on insect cuticular metabolism. The results showed that sulforaphane significantly modulated appressorium formation. Spore suspensions with varying appressorium formation rates were injected into and larvae. As the appressorium formation rate increased, exhibited enhanced pathogenicity, leading to accelerated larval mortality. A significant positive correlation ( ≤ 0.05) was observed between appressorium formation and pathogenicity. LC-MS analysis revealed that, prior to appressorium development, larvae activated defence mechanisms involving secondary metabolites, hormone signalling, and toxin metabolism pathways. Following appressorium formation, 61 unique cuticular compounds were identified, along with activation of host lipid metabolism (notably glycerophospholipid degradation), programmed cell death pathways (ferroptosis, necroptosis), and enhanced energy metabolism via the citric acid cycle-collectively indicating disruption of the epidermal defence barrier. Overall, appressorium development by significantly reshapes the metabolic landscape of the larval cuticle, thereby enhancing fungal virulence. This study provides a theoretical foundation for understanding the pathogenic mechanisms of .