Friday Parasite #40: Invading Japan

Those of us who live in the United States are familiar with the foreign organisms that changed our environment, like European starlings, kudzu, zebra mussels, the Asian fungus that killed off the American chestnut, and the other Asian fungus that nearly wiped out the American elm. But species from North America also get moved to other parts of the world, and given the right conditions they can become invasive and destructive too. Since I’m visiting Japan, let’s look at what happened when the North American pine wood nematode (Bursaphelenchus xylophilus) got accidentally got moved to Asia inside some packing crates early in the 20th century.

Adult pine wood nematodes live inside resin canals in pine trees, laying eggs inside the canals and feeding on the cells that line them. Generations of worms can live inside the tree, and as the canals fill up with nematodes, young worms molt into a special “dispersal” form and wait for a chance encounter with a larval pine sawyer beetle. When the wood-boring larvae blunders by, the young nematodes invade its respiratory system and set up housekeeping. When the beetle molts into an adult, it carries the worms to the next tree it visits.

In its native habitat, the pine wood nematode isn’t a pest. Pine trees native to North America put up with it with no ill effects. But when some worms got accidentally shipped to Japan, Japanese trees started dying. Quickly. Inside trees lacking resistance, the worm interferes with water movements inside the plant and can kill it in weeks.The picture below shows the progression of wilt in a Scotch Pine on the University of Nebraska, Lincoln campus over a twelve day period.

  

Of course, there are lots of non-native trees growing in the United States these days, so the pine wood nematode has  become a major pest of ornamental plantings and Christmas tree farms. If you’ve ever wondered why pine wood gets baked to within an inch of its live before it’s sent anywhere, you can blame Bursaphelenchus xylophilus.


Sources:
Hara, N., Y. Takeuchi and K. Futai 2006. Cytological changes in ray parenchyma cells of seedlings of three pine species infected with the pine wilt disease. Japanese Journal of Nematology 36(1): 23-32.

Global Invasive Species Database

University of California, Davis; Department of Nematology

Images:
Nematode: USDA Forest Service - Rocky Mountain Region Archives; UGA1442034; by J.J. Witcosky
Trees: University of Nebraska, Lincoln  Nematology

Comments

[Drhoz!]

I think you mean "to within an inch of its life."