## 3 Results
### Changes in Terpenoids in P. thunbergii after Inoculation with PWNs  
To further study the influence of the terpenoid synthesis pathway on the resistance of _Pinus thunbergii_, we chose 0, 24, 72 and 168 h after inoculation with PWNs in _P. thunbergii_ with different levels of resistance, to determine the types and contents of terpenoids. A total of 41 volatiles were detected in resistant and susceptible _P. thunbergii_. The pine needles over all time periods were measured (Supplementary Table S2, Figure 1), 39 terpenoids were detected in resistant _P. thunbergii_, 28 were detected in susceptible _P. thunbergii_, and 25 were detected in both. A comparison of the main terpenoids detected in _P. thunbergii_ with different levels of resistance at various time periods after inoculation by the PWN showed that, among the terpenoids common to _P. thunbergii_ with different levels of resistance, the relative percentage of oxyophyllene was higher in susceptible _P. thunbergii_ than in the resistant one at all inoculation stages. Additionally, the relative percentage of \(\alpha\)-pinene, \(\beta\)-pinene and germacrene Dwas higher, which are the key VOS of resistance in resistant and susceptible _P. thunbergii_. However, the relative percentage of \(\beta\)-pinene and germacrene D were higher in susceptible _P. thunbergii_ than in the resistant one. The relative percentage of \(\gamma\)-cadinene was consistently higher in resistant _P. thunbergii_ than in the susceptible one, but it showed a decreasing trend in resistant _P. thunbergii_ and the susceptible one. Seventy-two hours after inoculation, \(\beta\)-cis-ocimene appeared simultaneously in _P. thunbergii_ with different levels of resistance and occupied a higher relative percentage (17.28% in susceptible and 11.07% in resistant _P. thunbergii_), and 168 h of inoculation the relative percentage of \(\beta\)-cis-ocimene increased in resistant _P. thunbergii_ but decreased in susceptible _P. thunbergii_, its relative content was consistently higher than that of resistant _P. thunbergii_ at all times (Table 2). The analysis revealed 14 terpen specific to resistant _P. thunbergii_, of which eight terpen before and after inoculation with PWNs were cis-\(\gamma\)-bisabolene, linalool, alloaro-madendrene, germacrene B, bicyclogermacrene, dehydroasbienene, pseudolimonen, and \(\alpha\)-thujene. Furthermore, six of the 14 specific terpen appeared only after inoculation (i.e., inducible), including \(\alpha\)-terpineol, epi-\(\beta\)-caryophyllen, myrrtenal, benzene, n-butyl, cryophyllene oxide and sabinene. In contrast, only three terpen were unique to susceptible _P. thunbergii_, including \(\beta\)-cadinene and \(\alpha\)-muvurolene, which were present both before and after inoculation with PWNs, and borneol was detected after inoculation with PWNs (Table 3). Analysis of the content of the main specific terpenoids in resistant _P. thunbergii_ revealed that the relative percentage of sabinene (after inoculation with PWNs in resistant _P. thunbergii_) was higher, with values of 15.97%, 72 h after inoculation with PWNs and 18.89% 168 h after inoculation; the relative percentage of pseudolimonen (in resistant _P.