Chitin Deacetylase 8 Affects Epidermal and Peritrophic Membrane Metabolism in <i>Tuta absoluta</i> and dsRNA Accelerates Larval Death with <i>Bacillus thuringiensis</i>

<i>Tuta absoluta</i> is highly resistant to many common insecticides. Chitin deacetylase (CDA), an important enzyme in chitin synthesis and metabolism, may serve as a target for the management of <i>T. absoluta</i>. We cloned and identified <i>TaCDA8</i> using the polymerase chain reaction (PCR) and bioinformatics analysis. Quantitative real-time PCR (qRT-PCR) showed that the expression level of <i>TaCDA8</i> in the fourth instar larvae was significantly higher than in other developmental stages. Feeding ds <i>TaCDA8</i> significantly reduced larval survival and pupation rates, causing failed molting, impaired pupation, and peritrophic membrane (PM) damage. Combining dsRNA with a <i>Bacillus thuringiensis</i> (Bt) biopesticide agent increased mortality. These results confirm that <i>TaCDA8</i> regulates chitin metabolism in the PM and is key for epidermal development. <i>TaCDA8</i> is essential for larval growth, development, and resistance to pathogens. <i>TaCDA8</i> can be effectively targeted by the RNAi-Bt combination to enhance pest mortality. Therefore, <i>TaCDA8</i> represents a promising target for the development of highly efficient pesticides and green control strategies for integrated pest management.