Distribution of pine wood nematodes and their vectors

In this study, we investigated the distribution and density of the pine wood nematode Bursaphelenchus xylophilus in recently dead pine trees in coastal and inland regions ofSouth Korea, as well as the mortality rate of pine trees affected by pine wilt disease (PWD). In addition, we examined the seasonal emergence patterns of the Japanese pine sawyer Monochamus alternatus , the primary PWD vector, by monitoring its attraction to aggregation pheromone traps,to assess climate-driven variations in emergence timing. Surveys were conducted in May and June, from 2021 to 2023,across the three PWD-affected regions. In total, 35, 39, and 35 female M. alternatus individuals were collected in 2021, 2022, and 2023, respectively, and47, 55, and 50 males were collected, respectively. A density comparison between B. xylophilus and the co-occurring low-pathogenic B . mucronatus in the felled trees revealed a strong negative correlation, suggesting a potential competitive interaction between the two nematode species. In addition, M. alternatus density was significantly positively correlated with thedaily average temperature ( r = 0.786, 0.744, and 0.755 at Sites 1, 2, and 3, respectively), indicating that rising temperatures are associated with earlier vector emergence.