Comparison of transmission of Bursaphelenchus mucronatus via two different pathways from Monochamus saltuarius to host trees

Bursaphelenchus xylophilus, the causative agent of pine wilt disease, and B. mucronatus are transmitted by Monochamus adults to host trees. Feeding and oviposition wounds made by vectors are the primary transmission pathways to trees. Monochamus saltuarius female adults carrying B. mucronatus were reared singly and allowed to mate with nematode-free males at 5-day intervals, to determine the ratio of nematodes transmitted via the two different pathways. The survival time, lifetime fecundity and other reproductive traits decreased with increasing initial nematode load (number of nematodes carried by a newly-emerged adult). Model selection indicated that numbers of B. mucronatus departing from M. saltuarius and of those transmitted to pine via oviposition and feeding wounds were closely related to the initial nematode load, which was affected by survival time and number of oviposition wounds constructed. Most temporal patterns of nematode departure and transmission via oviposition or feeding wounds from individual vectors had a peak in the medium and heavy initial nematode loads. The nematode departure curve was significantly similar in shape to each of the nematode transmission curves via oviposition and feeding wounds, which were not significantly similar to each other, for individual vectors. After M. saltuarius females began to construct the oviposition wounds, it was estimated that B. mucronatus was transmitted via the oviposition wounds at a probability of 0.767. If B. xylophilus is transmitted in the same way as B. mucronatus, the incidence of pine wilt disease by mature vectors would be much lower than in the case of no oviposition-related transmission.