Population density of Monochamus alternatus adults (Coleoptera: Cerambycidae) and incidence of pine wilt disease caused by Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae)

Summary The seasonal occurrence of Monochamus alternatus and newly weakened trees were investigated in a Pinus thunbergii stand for 4 years. Adult beetles were present between June and September with a peak in their population occurring in early July followed by a decline then a period of about one month being in a steady number. The average number of Bursaphelenchus xylophilus (Nematoda), which is the causal agent of pine wilt disease, within beetles decreased as the season advanced. Pine trees newly weakened by B. xylophilus appeared between June and October, especially from August to October. The proportion of weakened or killed trees was directly proportional to the average beetle density per tree from June to August.