Comparison of transmission of the pine wood nematode, Bursaphelenchus xylophilus, via two different pathways from Monochamus alternatus to host trees

Abstract

Bursaphelenchus xylophilus causes pine wilt disease and is transmitted to host trees by cerambycid adults of the genus Monochamus. There are two primary transmission pathways: via vector feeding wounds to healthy trees and via the oviposition wounds to dying or recently dead trees. To determine the ratio of nematodes transmitted via the different pathways, M. alternatus female adults were reared on Pinus densiflora fresh twig sections and wood pieces with the bark made favourable for oviposition. Transmission curves of B. xylophilus to twig sections were similar in shape to the nematode departure curves for each vector, whereas the transmission curves to wood pieces were dissimilar to the departure curves because of different age classes at the peak between the curves. Consequently, there was no similarity in shape between two transmission curves to twig sections and wood pieces. Of B. xylophilus transmitted to twig sections and wood pieces after vectors constructed the first oviposition wound, 38.7% was transmitted to twig sections and 61.3% to wood pieces. Using the results of present and previous studies, GLM analysis indicated that the probability of B. xylophilus transmission to twig sections was 0.481 and that B. xylophilus had a 9.7 times higher likelihood of feeding-related transmission to oviposition-related transmission than non-pathogenic B. mucronatus. Thus, the reproductively mature vectors are considered to be related to the incidence of pine wilt disease and dispersal studies on mature vectors would help to predict the expansion rate of areas affected by the disease in the current year.