Pine wood nematode, pine wilt disease, vector beetle and pine tree: how a multiplayer system could reply to climate change.

The pine wood nematode, Bursaphelenchus xylophilus, constitutes a major threat to pine forests across the world. Under climatic conditions favourable to the expression of the pine wilt disease caused by the nematode, susceptible pine trees may die within a few months following nematode inoculation. Although considered a secondary pest in its native North America, this organism has caused huge damage in areas it has invaded in south-eastern Asia and south-western Europe. The nematode is carried by local long-horned beetles in the genus Monochamus, which vector it to pine trees first during maturation feeding and then when ovipositing. As climate is an important driver of insect vectors, nematodes and disease expression, we explore in this chapter how a changing climate could affect this multiplayer system in the future. Warming up is effectively susceptible to enlarging vector distribution, to accelerating its development and possibly to enhancing its flight performances. Therefore, it could change the time window of nematode transmission and increase the spread rate of the nematode. Other factors such as humidity, wind throws and forest fires could also affect vector population dynamics. Simultaneously, climate warming is likely to increase the development rate and reproduction of the nematode, and thus the nematode population growth. Finally, the expression of pine wilt disease is also modulated by warm temperatures and water deficit, causing drought stress to pine trees. With temperature increase, areas at risk of the disease would probably extend. Actually, pine wilt disease has recently been observed to expand its range in areas of eastern Asia that were previously considered as unsuitable. Modelling the disease spread helps to assess more precisely the potential effects of climate change and to evaluate the potential economic impacts.