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

Simple SummaryThe Chinese white pine beetle (Dendroctonus armandi) is a highly destructive forest pest that inflicts significant damage to coniferous ecosystems in the middle Qinling Mountains of China. Insect ATP-binding cassette (ABC) transporters are critically involved in mediating xenobiotic metabolism. However, the roles ofABCgenes in host terpenoid detoxification remain uncharacterized inD. armandi. In the present study, verapamil (an ABC transporter inhibitor) significantly increased beetle mortality induced by four monoterpenes. Then we characterized threeABCHsubfamily genes. All three genes were upregulated during developmental transitions and predominantly expressed in Malpighian tubules, fat body, and midgut. Notably,DaABCH1was significantly induced by α-pinene and limonene and silencingDaABCH1significantly increased mortality, which indicatedDaABCH1represents a critical candidate gene implicated in plant chemical defense mechanisms.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 ofABCgenes in the metabolism of host allelochemicals remain unclear inD. armandi. 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 byD. armandi. We then sequenced and characterized the full-length cDNAs of threeABCHsubfamily genes (DaABCH1–DaABCH3) fromD. armandi. 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,DaABCH3expression was detected in the hindgut and brain. Furthermore,DaABCH1andDaABCH2were significantly induced by treatment with α-pinene and limonene, whereasDaABCH3was induced by β-pinene and limonene. Importantly, silencingDaABCH1significantly increased mortality in adults fumigated with α-pinene and limonene. These results strongly suggest thatDaABCH1acts as a key regulator modulatingD. armandi’s sensitivity to host plant allelochemicals. This finding provides a conceptual basis for developing novel control strategies against this economically significant forest pest.