## 1 Introduction
Its surface color is different, and its texture is hard and heavy. Authentic agarwood has a strong, lasting aroma during combustion and leaves no black carbon residue afterwards [17]. However, counterfeit agarwood produces an unpleasant odor during burning, and the burning ash leaves a black carbon residue [18]. At present, the quality of agarwood is mainly determined using high-performance liquid chromatography (HPLC) by identifying the contents of the main indicator compounds of agarwood. For instance, agarotetrol is the main active ingredient of agarwood and can be used as a potential quality marker [19]. In addition, agarwood contains more than 300 compounds. These include flavonoids, sesquiterpenes, and 2-(2-phenylethyl) chromones [20], with the latter two displaying the widest range of pharmacological activities, and their contents and concentrations are often used as criteria for evaluating the quality of agarwood [20; 21]. That being said, there are a variety of aromatic compounds and pharmacologically active ingredients in agarwood that are important factors for determining its quality [22; 23]. Sesquiterpenenes are important compounds in agarwood and have been widely studied. Sesquiterpene biosynthesis in agarwood involves two pathways--one is the MVA pathway that starts in the cytoplasm and the other is the MEP pathway that starts in the plastid [24,25]. In the MVA pathway, AACT is the primary enzyme acting in the initial stage. HMGS and HMGR are the key enzymes responsible for the conversion of acetyl-CoA to mevalonate in the second and third stages. MVK and PMK cause phosphorylation. In the final stage, MVD acts as the rate-limiting enzyme during the synthesis of the terpenoid precursor IPP in the MVA synthesis pathway. These enzymes have been identified as homologous genes [26]. In the MEP pathway, DXS is the primary rate-limiting enzyme in terpenoid biosynthesis, and DXR, MCT, CMK, MDS, and HDR also play important regulatory roles. The general precursor of terpenoid synthesis is formed via these two pathways, and then the monoterpene precursor, GPP, the sesquiterpene precursor, FPP, and the diterpene and tetraterpene terpenoid precursor, GGPP [27], are synthesized by GPPS [28], FPS, GGPPS, and other enzymes. Finally, the terpenoid synthase TPS reacts with these terpenoid precursors through a series of modification reactions to further generate terpenols, aldehydes, acids, esters, and other derivatives [29,30]. The purpose of this study is to explore the dominant strains and wood-eating insects that promote the formation of agarwood in _A. sinensis_ and to examine its induction through physical damage, fungi, wood-eating insects, and fungal infections combined with insect damage. The content of agarotetrol in the samples under different treatments was used to identify the best way to promote and improve the efficiency and quality of agarwood formation in _A. sinensis_ using the 'insect + fungus' method. At the same time, a transcriptome analysis of agarwood samples under different treatments was carried out in order to explore the mechanisms of agarwood induction by insects combined with fungi, to find the key genes and transcriptional regulators of the sesquiterpene synthesis pathway of agarwood, to provide experience and reference for the future development and promotion of stable, efficient, environmentally friendly, and sustainable artificial induction methods of agarwood in _A. sinensis_, and to offer a theoretical basis for exploring the formation mechanism of agarwood.