Bursaphelenchus xylophilus

Bursaphelenchus xylophilus, commonly known as pine wood nematode or pine wilt nematode (PWN), is a species of nematode that infects pine trees and causes the disease pine wilt. It occurs in much of the United States, Canada, and Mexico. It also occurs in Japan, China, Taiwan, Korea, and Portugal. Pine mortality in Japan was first reported Munemoto Yano (矢野宗幹) in Nagasaki prefecture in 1905. The nematode was first discovered in the timber of longleaf pine (Pinus palustris) in Louisiana, United States. Steiner and Burhrer reported that the nematode was a new species, and they named it Aphelenchoides xylophilus in 1934.In 1969, Japanese plant pathologists Tomoya Kiyohara (清原友也) and Yozan Tokushige (徳重陽山) discovered many unfamiliar nematodes on dead pine trees around the Kyushu islands in Japan.Then, they experimentally inoculated the nematode to healthy pine and other conifer trees and observed them. The healthy pine trees were killed—especially Japanese red and Japanese Black pine. However, Jack and Loblolly pine, Sugi cedar, and Hinoki cypress trees were able to survive. The researchers concluded that the nematode was the pathogen behind the increase of mortality in Japanese pine trees. In 1972, the year after the ground-breaking paper of Kiyohara and Tokushige was published, Yasuharu Mamiya (真宮靖治) and T. Kiyohara posited that the nematode was the pathogen behind pine mortality, and that it was a new species. They named it Bursaphelenchus lignicolous . Bursaphelenchus lingnicolous, the Japanese nematode, was re-classified as the American species B. xylophilus in 1981. Pine wilt nematode epidemics have occurred in Japan, particularly during warm, dry summers. Species of the genus Bursaphelenchus are difficult to distinguish because they are similar in morphology. A positive identification can be made with molecular analyses such as restriction fragment length polymorphism (RFLP). B. xylophilus is distinguished by three characteristics: the spicule is flattened into a disc-shaped cucullus at the tip, the front vulval lip is flap-like, and the tail of the female is rounded. The pine wilt nematode has a typical nematode life cycle, with four juvenile stages and an adult stage with both male and female individuals that reproduce sexually. The mycophagous phase of the life cycle takes place in dead or dying wood, where the nematodes live and feed upon fungi, rather than the wood itself. The nematode cannot travel outside of the wood independently; it must be transported by an insect vector.