Up and down the street in Prince George’s County, Maryland, ash trees are dead or dying. The stately hardwoods are being killed by a shiny green beetle from Asia called the emerald ash borer. It’s an invasive species that has wiped out more than 30 million trees since it hitchhiked from China on a shipping crate more than a decade ago.
The beetles threaten not only to eradicate one of the most popular suburban shade trees in America, but also to harm water quality in rural streams, by removing trees that cool and filter waterways.
At first, Maryland officials tried to contain the bark-burrowing leaf eaters by cutting down trees to deny them food. But that didn’t work.
And so now the bug hunters are playing hardball: they’re pitting exotics against invasives. Over the last year, the Maryland Department of Agriculture has released more than 9,000 Chinese parasitic wasps here, with the hope that they will prey upon the emerald ash borer, as they do in Asia.
“The theory behind biological control,” explained Dick Bean, entomologist with the state agency, “is that you go back to the native country of origin, you look for any sort of organisms that are able to keep the thing in check, that you can rear in some laboratory and release in the field, and allow them to maintain the checks and balances that occurred back in its native range.”
The wasps (such as Tetrastichus planipennisi, pictured at left) do not sting humans. But they use terrifying-looking drills to inject their eggs into live ash borer larvae. It’s a little like the movie “Alien.” Inside the bodies of their hosts, the wasp larvae grow until they’re big enough to erupt out, killing the ash borers.
“It’ll give you nightmares, if you think about it too much,” Bean said.
The problem is, this strategy –- using alien species as population control agents -– gives some ecologists nightmares.
“There are no shortages of ecological disasters associated with biological control,” said Dan Herms, a professor of entomology at Ohio State University. “There are a number of notorious examples where they have had serious impact on native species beside the target.”
In other words, sometimes good bugs go bad. For example, a parasitic fly introduced to control invasive gypsy moths early in the 20th century did nothing to stop the gypsy moths. But the flies had a devastating impact on native silk moths.
Carnivorous snails, called rosy wolf snails, were introduced into Hawaii to attack invasive giant African snails, which were swarming over farms. The African snails were not bothered by the competition. But the ravenous wolf snails caused the extinction of several native snail species.
Daniel Simberloff, a professor of environmental studies at the University of Tennessee, said he’s concerned that the introduction of parasitic Asian wasps into Maryland could kill off native jewel beetles similar to the emerald ash borer.
Invasive species have become increasingly common as globalization has multiplied traffic between continents. But Simberloff said this tactic of introducing exotic species to control invasives only succeeds about 10 percent of the time. More often, he said, it fails. Occasionally, however, he said it works very well. For example, importing Argentinian flea beetles suceeded in controlling alligator weeds in Florida.
“Some of those successes are really spectacular successes," Simberloff said. "And once you do it, it’s not like you have to keep doing it again, if the biocontrol agent has established itself as a population. It reproduces itself. So unlike spraying a chemical, you don’t have to go out and buy it each year and spray it. So when it really works, it more or less solves the problem in perpetuity.”
Dick Bean, from the Maryland Department of Agriculture (pictured at right, holding a vial with Chinese wasps), said the wasps that he released were first tested in the lab, where they showed a preference for emerald ash borers over other insects. So he believes the risk of collateral damage is low.
Now, whether low risk is safe enough when we’re manipulating the balance of life ... only time and the trees will tell.
By Tom Pelton, Chesapeake Bay Foundation
Photos by Tom Pelton (top and bottom) and U.S. Department of Agriculture (middle)
Hi all!
I want to bring up his daughter Sitemap of countrywide home loans simi valley I want the general and mental well-being John symonds aussie home loans I want to increase efficiency Sitemap of swingline loans
We will not miss you
Posted by: Linytonsict | 12/22/2011 at 04:20 AM