Nematode Fauna and Fungal Flora in Infected Pine Trees

Abstract

In Japan the pine wood nematode (PWN) is transmitted mainly by the Japanese pine sawyer, Monochamus alternatus, from wilt-killed to healthy pine trees (Mamiya and Enda 1972; Morimoto and Iwasaki 1972). The adult beetles of M. alternatus carry a great number of PWNs in their tracheae when they emerge from PWN-killed pines in early summer. Newly emerging adults fly to healthy trees and feed on the bark of young twigs for maturation of their reproductive organs (maturation feeding). At that time, the PWNs on the vector beetles are transmitted to healthy trees and invade them through the feeding wounds made by the beetles. A small number of PWNs disperse widely in the infected trees and causes cessation of oleoresin flow. Thereafter, PWNs propagate dramatically and the trees show wilting symptoms, releasing volatiles such as ethanol, and terpenes (reviewed by Kishi 1995). Mature beetles are attracted to these wilting trees and oviposit in them. The eggs hatch within a week and the larvae feed on the inner bark and outermost sapwood, and then in autumn bore into the sapwood to form pupal chambers (PCs). The number of PWNs reaches its maximum from autumn to winter, and then decreases gradually (Mamiya et al. 1973; Fukushige and Futai 1987). The PC of M. alternatus beetles is one of the most important places for PWNs, because as Mamiya (1972) reported numerous PWNs aggregated around the PCs of M. alternatus in wilt-killed pine trees and that the beetles emerging in the subsequent year harbored many nematodes on their bodies.