Stingless wasps are newest weapon against emerald ash borers

The next big things in the fight against the emerald ash borer are three tiny wasps that can't even sting.

Researchers expect to release several hundred of the three species of wasps in Minnesota within weeks as part of an experimental effort to combat the emerald ash borer, a pest that has no known natural foes and threatens Minnesota's 900 million ash trees. The hope is that the wasps will help foresters slow down the spread of the ash borer by killing them and will be more successful than tree removal, insecticides, quarantines and public service announcements.

"I would not use the words 'silver bullet' at all," said Paul Chaloux, coordinator of the U.S. Department of Agriculture's wasp program. "But it's the most promising tool we have right now."

Officials with the Minnesota Department of Agriculture, the lead agency in Minnesota's ash borer war, received a federal permit to release the wasps but are waiting to find a fresh emerald ash borer emergence in a choice location. Minnesota would be the sixth state to get the wasps, which like the ash borers are native to China. Scientists are rearing the wasps in a Michigan laboratory for eventual use against the ash borer, which has been detected in 14 states and two Canadian provinces.

Monika Chandler, a research scientist with the agriculture department, said the wasps -- which range from gnat- to ant-sized -- shouldn't alarm people.

"I don't think people understand wasps come in this size," she said. "If people saw them, I think they'd be quite reassured."

That they don't sting people (most wasps don't) is another plus, Chandler said. But what they do to ash borers is worthy of a horror film.

In China, the three species destroy 50 to 90 percent of the ash borer eggs or larvae they encounter. And researchers are moving quickly, by research standards, to see whether the same dynamic can be established in North America, where the ash borer has run rampant since it was first detected near Detroit eight years ago.

The first U.S. release of the parasitic wasps occurred in 2007, and the federal wasp-rearing lab in Michigan opened a year later. "That's pretty fast, even from the point of view of an insect," said Jonathan Lelito, manager of the EAB Biological Control Facility in Brighton, Mich.

One obvious question about the program is whether it's wise to fight one exotic, invasive species by introducing another. The U.S. Department of Agriculture has determined that the wasps aren't a threat to anything other than ash borers, a finding that underpins Minnesota's permit to release them. Unchecked, the USDA estimates, the ash borer could spread to 25 states in the next 10 years, costing public and private tree owners $10 billion in damage.

Don Arnosti, policy director for Minnesota Audubon and forest program director for the Institute for Agriculture and Trade Policy, noted that while environmentalists might customarily be alarmed by the arrival or introduction of any foreign species, it's too late to take that stance with ash borer-fighting wasps. Letting the nation's 8 billion ash trees succumb to the ash borer would eliminate an important species in the environment as well as a source of commercially valuable wood.

But Arnosti argued that it might have been wiser and cheaper to have spent millions of dollars years ago to design and enforce controls on the movement of exotic species through shipping and travel. Ash borers are believed to have arrived in North America in wooden packing crates from China in the 1990s.

Lelito and Chandler noted that it will take several more years to answer key questions about whether the wasps might head off the ash borers' spread across the continent. One question is how long it might take for the wasps to protect trees that, unlike those in the ash borer's native China, have no resistance of their own to ash borers. Also uncertain is whether they might be eaten by woodpeckers or be unable to survive Minnesota winters. "Biological control, when it's effective, is extremely successful from both an environmental perspective and cost effectiveness," said Chandler, noting that it's been used in Minnesota to combat leafy spurge, an agricultural menace, and gypsy moth, a forest scourge. "Once it gets out there, it's self-sustaining."