More than 25 million ash trees have been lost across Michigan, Indiana, Ohio, Illinois and Ontario since the Emerald Ash Borer arrived in the 1990s.
“Bringing in an exotic species to control an invasive species can create a lot of problems,” says Dr. James Dunn, a former forest entomologist for the Forest Service who now teaches biology at Grand Valley State University in Michigan. “Once it’s out there, there’s nothing we can do. It’s going to cost the taxpayers, we can’t control it and it’s got a low probability of working. They know that,” he says. “The researchers are on mission-driven research. They’re getting paid to find a species. What bothers me the most is they should at least be honest about the probabilities.”
The use of biological control has had mixed results in the past. When the Asian lady beetle was released in the U.S. to control aphids, it did a fantastic job, but it didn’t stop there. It spread across the country, becoming a household pest in some areas while leaving native ladybugs with little or nothing to eat. It’s also suspected to have played a role in the extinction of the nine-spotted ladybug, New York state’s official insect.
When the mongoose was introduced to Hawaii, Jamaica and Puerto Rico to control rats in sugarcane, it developed a taste for ground-nesting birds, reptiles and amphibians. It now costs these areas due to the loss of native species and poultry and is responsible for at least three species extinctions.
“Native species have a better probability of controlling the invasive species. It can take years, but they adapt and take it over,” says Dunn. “It’s a better way to let nature rebalance itself than to bring in more exotics.”
Risk studies on the wasp introduction looked at what other larvae they may attack, says Lucik. The wasps were found to be host-specific to EAB. However, the federal proposal to release the wasps acknowledges, “there is a slight possibility they could move from the target insect (EAB) to attack non-target insects,” adding that “the resulting effects could be environmental impacts that may not be easily reversed.”
Dr. Clement Hamilton, vice president of arboretum programs and director of research at The Morton Arboretum in Lisle, Illinois, says the risks are worth it. “The potential benefits of introducing the three parasitoid wasps significantly outweigh the risks,” says Hamilton, “especially when one considers the ecological and economic devastation that EAB is creating in the absence of effective control.”
The use of biological control does present a reasonable alternative to the use of pesticides and cutting. Researchers are now developing an aerial spray of Bt, the pathogen used in genetically modified foods to repel insects. “We have a good Bt that kills EAB and we’re working with companies to develop the spray,” says Bauer. Unlike the wasps, which will reproduce naturally, the aerial spray will have to be repeated at substantial costs, and with toxic side effects.
In addition, 47 states have adopted a trapping program. The traps are two-feet long, three-sided and purple, and will be hung from ash trees and placed around the trunks. “They’re going to be a spectacle,” says Lucik.
CONTACTS: The Emerald Ash Borer, www.emeraldashborer.info; Purple EAB Survey, www.purpleeabsurvey.info.