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An army of tiny Chinese wasps to save Colorado trees

In a desperate bid to save its trees, Colorado is turning to an army of tiny wasps from China.

Over the next six weeks, more than a thousand stingless, parasitic wasps will be released to combat the threat posed by the emerald ash borer (EAB), a destructive, non-native tree pest that poses a threat to the state's urban forests. This week, the first 200 gnat-sized Oobius agrili will be released at infested sites including the campus of the University of Colorado, where they will target the ash borer eggs.

The ash borer has been blamed for the death of tens of millions of ash trees in the United States. It was confirmed Boulder in September 2013 and there are fears it could spread across the state, since it can fly up to a half-mile to infest new trees.

Emerald ash borer adults, half-inch-long, emerald-green beetles, are now flying to lay eggs on new host trees. This is the best time of year to detect them visually. Dan West, CSFS entomologist

"We're hoping that by releasing biocontrols like these, we can slow the spread and better manage the impacts of emerald ash borer in Colorado," said John Kaltenbach, biological control specialist for the Colorado Department of Agriculture.

Oobius agrili locates the eggs in crevices of tree bark and inserts its own eggs inside the host egg. When the eggs hatch, the wasp grows and eventually kills the ash borer larvae before they can do any damage to trees.

Authorities believe the stingless wasp poses no threat to people or pets.

This is the second species of ash borer parasitoid to be released in Colorado. In 2014, the team released the stingless wasp Tetrastichus planipennisi, which targets the ash borer larvae developing under the bark of ash trees.

These control efforts date back to 2002, when the U.S. Department of Agriculture implemented them in Michigan after studying three so-called biological controls, other organisms that attack the ash borer in its native range of China: Oobius agrili, Tetrastichus planipennisi and Spathius agrili.


After studying their effects on the ash borer, they were released in Michigan in 2007. These days, the EAB Biological Control Production Facility rears the wasps for mass release. One or more wasp species have been released in 19 of the 25 states where ash borer has been found.

The ash borer is just one of several pests afflicting trees across the country, with other threats being a toxic fungus and the mountain pine beetle.

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