The severe damage to pine trees (Pinus densiflora and P. thunbergii) in the stands throughout southwestern Japan had been attributed to the attack of bark beetles of the families Cerambycidae, Curculionidae and Scolytidae. These beetles do not attack the bole of healthy pine and oviposite only into the weakened or dead one (Oda, 1967; Iwasaki and Morimoto, 1970 & 71). Tokushige and Kiyohara (1969) found a nematode of the genus Bursaphelenchus in wood of the damaged pine trees collected from many localities in Kyushu. Kiyohara and Tokushige (1971) first claimed after their inoculation experiments that this nematode might be one of the main causal agents for the death of pine trees and played an important role in the deterioration of pine forests in southwestern Japan. This nematode is to be named by Mamiya and Kiyohara (in press) as Bursaphelenchus lignicolus.
From the investigations conducted in 1971, it was confirmed that pine longicorn, Monochamus alternates, plays an important role as a vector of Bursaphelenchus lignicolus, and transmits Dauerlarven of the nematode into healthy pine trees via fed wound on twigs and branches mostly from the middle of May to the beginning of August, and to less extent thereafter.
Results obtained are as follows:
1) The authors examined more than 2000 insects and found that 71% of Monochamus alternatus emerging from damaged trees were infested with Bursaphelenchus lignicolus with an average burden of 3146 nemas of the Dauerlarven form. They were recovered from the underside of elytra and spiracles, especially from the first abdominal apiracles (Tab. 1, 2, 3).
2) More than 80% of the Dauerlarven of the nematode are estimated to fall off gradually and randomly from the body of longicorn between the emergence and the beginning of the oviposition (Tab. 4, 5).
3) Dauerlarven of the nematode, fallen on twigs or branches, moulted on the fed wound and entered into xylem within a considerably short time. This namatode was also recovered from the fed wounds of Monochamus alternatus in natural pine trees (Tab. 5).
4) All the healthy pine trees wrapping some branches in nets and reared several new adults of this longicorn in them were dead in about one month after setting supposedly by the influence of the nematode.
5) Dauerlarven of the nematode were also recovered from mounted and alcoholic specimens of Monochamus alternatus (Tab. 6).