Case Study: Pine Wood Nematode

The pine wood nematode Bursaphelenchus lignicolus, a microscopic worm, has plagued the forests of Japan for a century. Although transmitted by the Japanese pine sawyer, an indigenous longhorn beetle, this nematode is an alien invasive species. First observed in a Louisiana sawmill, the nematode was introduced in 1905 on the southern island of Kyushu, probably in a shipment of U.S. timber or packaging material. It has spread steadily northeastward since introduction and now extends into the forests of Okinawa, Taiwan, South Korea, North Korea, and China. The pine wood nematode occurs in 28 U.S. states, but causes little direct damage in the United States.

The nematode attacks the vascular tissue of pines, resulting in wilt and death within one year. Japanese black and red pines are especially susceptible to this disease and the current epidemic, which is the fourth since its introduction, killed enough trees in one year to build 50,000 houses. The previous epidemic, peaking in 1979, lasted a decade and caused a loss of 2.4 million cubic meters of pine wood.

The pine wood nematode is adapted to surviving unfavorable environmental circumstances such as dry conditions, low temperatures, and lack of food. This allows the nematode to take advantage of pines weakened after drought; thus pine mortality following dry periods is high. In addition, the pine wood nematode reproduces quickly, with a single female producing 230,000 offspring under ideal conditions.

Control of this pathogen varies. The Japanese pine sawyer, or longhorn beetle, which serves as the primary vector for the nematode, can be controlled with insecticides. Trunk injection of nematicides has been used in Japan, but this must be performed before any symptoms occur. Research is now being conducted on the possibility of breeding resistant trees, as different species of pine vary in their resistance. Once infection has occurred, however, the only effective method of control is to burn the infected trees.

Related Links:
-- ^{http://ucdnema.ucdavis.edu/imagemap/nemmap/ent156html/nemas/bursaphelenchusxylophilus
-- http://www.forestry.ubc.ca/fetch21/chinapwn/china96.html}