Global Future Modeling of the Monophagous Pest Pagiophloeus tsushimanus (Coleoptera: Curculionidae): An Integrated Approach Using Random Forest and the CLIMEX Model

Pagiophloeus tsushimanus Morimoto, 1982, a camphor tree weevil, is an emerging invasive wood-boring pest that has resulted in a progressive decline of Cinnamomum camphora plantations in affected areas. Native to Tsushima Island, Japan, P. tsushimanus has also spread to eastern China. With global climate change, the geographic range, occurrence frequency, and severity of this pest are continuously increasing, particularly in affected areas of China. Therefore, to limit the continued spread of this pest, the Random Forest (RF) algorithm and the CLIMEX model were combined to map the potential global distribution of P. tsushimanus. The results indicated that the potential range of C. camphora was jointly regulated by moisture availability (BIO18) and human modification indicators (PD and gHM). In contrast, the geographic distribution limits of P. tsushimanus were primarily defined by cold stress thresholds at higher latitudes and by heat and dry stress limitations in its traditional subtropical core range. Under current climatic conditions, the host-constrained suitable habitat of P. tsushimanus covered 4238.03 × 104 km2, mainly in East Asia, the southeastern United States, southeastern South America, and the Mediterranean coast of Europe. Under future climate change scenarios, P. tsushimanus and its host, C. camphora, exhibit a highly convergent poleward range expansion. New suitability hotspots for P. tsushimanus were projected to emerge in central and northern China, western and central Europe, and the northeastern United States. Owing to increased heat and drought stress in low-latitude subtropical core areas, the global suitable area under future climate change contracted by 17.99% overall, and highly suitable habitat decreased by 39.22%. The suitability maps of P. tsushimanus generated under host-constrained conditions in this study provide a potential early-warning layer for global forest health. We recommend that forestry departments in newly suitable temperate zones implement strict phytosanitary inspections of imported C. camphora nursery stock and that the timber and forest-product industries establish active monitoring programs to prevent the accidental introduction and establishment of this cryptic wood-boring pest.