Pine Wilt Disease Risk Is Determined by Water Vapor Pressure, Maximum Temperature, and Beetle Vector Distribution

Pine wilt disease (PWD), caused by the nematode Bursaphelenchus xylophilus, is a major threat to pine forests globally. The development of the disease is dependent on multiple variables, including presence of the nematode and its beetle vector and potential host plant identity, as well as environmental and anthropogenic variables. The complexity of PWD, arising from interactions between multiple components of the disease, presents great challenges to predicting the risk of disease occurrence. This study employed a multivariate modeling framework that integrated GeoDetector, eXtreme Gradient Boosting (XGBoost), and SHapley Additive exPlanations (SHAP) models to analyze key variables influencing PWD risk in China. The precision and accuracy of the results were benchmarked against the Random Forest method. Among the seven environmental variables, water vapor pressure (Vapr) was the most important variable affecting PWD infestation, followed by average maximum temperature (Tmax) and distribution of the beetle vector Monochamus saltuarius (BV1). Furthermore, these variables interacted synergistically and exacerbated disease risk. Spatially, areas with the highest PWD risk were closely associated with Vapr ranging from 2.37 to 2.75 kPa and Tmax ranging from 29.3 to 30.8°C. Areas with moderate risk were associated with Vapr ranging from 1.63 to 2.37 kPa and Tmax ranging from 26.1 to 29.3°C, while areas with low risk were associated with Vapr < 1.63 kPa and Tmax < 26.1°C. Among the anthropogenic variables, distance to ports was the most influential, with areas within a 3-km radius showing the highest risk of PWD. These results indicate that timber trading, both domestic and international, is responsible for the long-distance spread of the disease. Thus, PWD prevention measures should target areas with high Vapr (2.37 to 2.75 kPa) and high Tmax (29.3 to 30.8°C). In addition, stringent biosecurity measures at trading hubs should be in place to arrest spread of the disease.