Opinion: Wasps Imported to Save Ash Trees


It’s been a sad few years for Minnesota. But, maybe the end is in sight.

When I lived there in the 1970s, the state was plagued with Dutch elm disease. The vicious little elm bark beetle came from Asia in wooden packing crates and attacked elm trees by the millions, killing them by boring under the bark and cutting off the flow of sap.

The state department of natural resources organized cutting and disposal crews, armed them with chainsaws and sent them out to cut down every diseased tree in the state.

The trees numbered in the millions. Unfortunately, because of the pervasive nature of the beetles, the trees could not be used for lumber or for firewood. Instead they were dumped into yawning pits hastily dug with bulldozers. Every community had one, and when all the trees had been dumped into them, they were sprayed with insecticide and covered with dirt.

It was a tragedy of epic proportions because the elm tree was Minnesota’s most popular shade tree. Streets were lined with them. I had three in my back yard.

Perhaps no town was more drastically affected than Mountain Lake, a small college town south of the Twin Cities. Main Street was also the highway that ran through the middle of town. Both sides of the street were lined with huge elm trees that joined their branches overhead forming a picturesque tunnel. In the spring the air was light green from emerging foliage. In the fall the light turned amber. Everyone slowed down to enjoy the drive through Mountain Lake.

Then the chainsaws came, the trees were cut down and the town was reduced to a moonscape. The city fathers met and declared they would rebuild with new trees. They planted ash trees. Other cities followed suit and soon willowy ash saplings were filling the gaps left by the elms.

Then a new plague arrived, also from Asia, and also in wooden packing crates. The emerald ash borer marched across the state and found a banquet waiting. The insects were first discovered in 2002 in Michigan. They multiplied rapidly and quickly became a lethal threat to Minnesota ash trees, including those along Main Street in Mountain Lake.

But this time tragedy may be averted. A solution may have been found to save the trees. Minnesota just announced the import of a stingless wasp known to the scientific crowd as Tetrastichus planipennisi. The wasp is a parasite which lays its eggs under the bark of the ash tree, and the larva attacks the ash borer.

And, oh yeah, the wasp also comes from Asia.

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