Distribution of pine wilt disease with respect to temperature in North America, Japan, and Europe

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Abstract
In regions of North America and Japan where the pinewood nematode, Bursaphelenchus xylophilus, and its insect vectors occur, pine wilt disease in susceptible pines appears to be expressed only where the mean air temperature exceeds 20.degree. C for protracted periods. In these warm areas, susceptible pines grow disease-free only at the cooler, high elevations. Pines resistant to pine wilt transcend the 20.degree. C temperature threshold without becoming diseased. There are no reports of susceptible pines dying of pine wilt in those regions of Europe, North America, or Japan where mean summer air temperatures are less than 20.degree. C, despite the presence of pinewood nematode and its vectors in these regions. Bursaphelenchus xylophilus is found throughout most of North America; has been reported from Siberia, China, and France; and is regarded as an introduced pathogen in Japan. We hypothesize that it occurs throughout most taiga forests of the northern hemisphere where predominantly cool climates prevent widespread expression of pine wilt disease. The cool climates of much of Europe, North America, and Asia mitigate against the occurrence of pine wilt disease should B. xylophilus be inadvertently introduced. Susceptible pines that are transplanted from cool to warm regions will be at risk to the disease.