RNAi-Based Insecticide Target Screening: Four Genes Critical for Cuticular Pigmentation and Molting in Beetles

<i>Monochamus alternatus</i>, a destructive pine-boring pest, urgently requires finding alternatives to chemical pesticides for its eco-friendly control, such as RNA interference (RNAi)-based pesticides. This study screened potential RNAi targets by investigating cuticle-associated genes involved in pigmentation and molting. Silencing <i>tyrosine hydroxylase</i> (TH) induced albinism in pupae and adults and reduced pupation rates with 74.8% adult corrected mortality, and TH inhibitors exhibited dose-dependent effects, with high doses causing complete larval mortality. Targeting <i>ultraspiracle</i> via two dsRNAs severely disrupted molting in fourth-instar larvae, resulting in 77.6% and 87.9% corrected mortality. <i>Chitin deacetylase 2a/2b</i> (<i>CDA2a/2b</i>), highly expressed in the integument and legs, led to lethal molting defects when silenced individually, with corrected mortality rates of 91.6% and 95.8%. Notably, <i>CDA2b</i> silencing showed the strongest lethal effect. This research identifies four key target genes for RNAi-based pesticides against <i>M. alternatus</i> and presents new methodologies for RNAi control strategies applicable to other agricultural pests.