Transcriptional Response of ABCH Transporter Genes to Host Allelochemicals in <i>Dendroctonus armandi</i> and Their Functional Analysis

Bark beetles depend on detoxifying enzymes to counteract the defensive terpenoids produced by host trees. Insect ABC transporters play a critical role in the detoxification of insecticides and plant secondary metabolites. However, the specific functions of <i>ABC</i> genes in the metabolism of host allelochemicals remain unclear in <i>D. armandi</i>. In this study, we observed that verapamil significantly enhanced the mortality of host allelochemicals in beetles, indicating that ABC transporter genes are involved in the metabolism of monoterpenes by <i>D. armandi</i>. We then sequenced and characterized the full-length cDNAs of three <i>ABCH</i> subfamily genes (<i>DaABCH1</i>–<i>DaABCH3</i>) from <i>D. armandi</i>. Spatiotemporal expression profiling revealed that all three genes were upregulated during developmental transitions (egg to larva and pupa to adult) and tissue-specific enrichment in detoxification-related organs (Malpighian tubules, fat body, and midgut). Additionally, <i>DaABCH3</i> expression was detected in the hindgut and brain. Furthermore, <i>DaABCH1</i> and <i>DaABCH2</i> were significantly induced by treatment with α-pinene and limonene, whereas <i>DaABCH3</i> was induced by β-pinene and limonene. Importantly, silencing <i>DaABCH1</i> significantly increased mortality in adults fumigated with α-pinene and limonene. These results strongly suggest that <i>DaABCH1</i> acts as a key regulator modulating <i>D. armandi</i>’s sensitivity to host plant allelochemicals. This finding provides a conceptual basis for developing novel control strategies against this economically significant forest pest.