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Marines help save Ryukyu pine trees of Okinawa from natural enemies

Date Posted: 2004-04-15

JUNGLE WARFARE TRAINING CENTER, Okinawa, Japan — Chain saws and axes are often a tree’s greatest enemy, but for the Ryukyu pine trees in Okinawa, their greatest enemies are small, worm-like parasites called nematodes and their host carrier the pine sawyer beetle.

The two predators symbiotically exist together and attack native pine trees of Okinawa by using each other’s naturally selected attributes to infest the trees.

“A nematode is a tiny organism about one millimeter long,” said Mitsugu Sugiyama, natural resources specialist, Marine Corps Base, Environmental Branch. “They cannot move one place to another so they use the beetle as a vehicle to move from tree-to-tree.”

Sugiyama said nematodes move from tree-to-tree searching for a suitable source of food. They bore holes in the wood, which in turn provides the nematodes a place to enter and destroy the vascular system of the trees.

“The beetles need dead trees to reproduce, the nematodes kill the trees, and the beetles breed inside,” said Sugiyama.

Accidentally introduced to Okinawa from imported lumber from mainland Japan for dam and road construction in 1973, the beetles and nematodes have been threatening the pine trees of Okinawa for more than 30 years.

“If we lose this tree, it will change the whole natural image of Okinawa,” said Steve P. Getlein, natural and cultural resources manager, Marine Corps Base, Environmental Branch. “If the pine is lost, then the island is prone to invasion by exotic species of trees.”

Marine Corps and Japanese Government's Defense Facilities Administrative Bureau have been conducting surveys throughout the Central Training Area to prevent the beetles and nematodes from causing further damage. Scientists are unsure of how long it would take for the pine trees to be wiped away from the island.

As a preventative measure, the Marine Corps and DFAB have invested more than $10 million this year in cutting and burning more than 2,000 infested trees. The infested trees are cut into lengths and airlifted by helicopter to a burning site in order to stop the spread of nematodes and beetles, according to Sugiyama.

“If burning them is not an option, we can put tents over the infested trees and pump chemicals in to kill them, but this can take weeks to do,” said Getlein.

Alternative method scientists are to introduce natural enemies such as other beetles, birds, or reptiles to control the population growth of the pine sawyer beetle, or to select Ryukyu pine trees naturally resistant to nematodes and reforest the island with the resistant trees.

“The prefecture has a plan to divide the island into zones and eradicate the beetles one zone at a time,” said Getlein.

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