Unleash the Wasps Controversial Measures to Save the Nation's Ash Trees

Hundreds of Chinese wasps, each no larger than a sesame seed, were released in Michigan last summer in the latest effort by the United States Department of Agriculture (USDA) to control the Emerald Ash Borer (EAB).

The tiny iridescent green beetle hitched a ride in cargo from Asia to Michigan in the 1990s and decimated more than 25 million ash trees in Michigan, Indiana, Ohio, Illinois and On-tario before bringing its path of destruction to Maryland, Virginia and Pennsylvania. The assassin beetle attacks all species of ash, regardless of a tree’s health. The adults nibble on the foliage, but it’s the larvae that finish them off, eating the inner bark of the trees and blocking the movement of water and nutrients from roots to leaves. The USDA Forest Service estimated that it could cause approximately $7 billion in additional costs to state and local governments and landowners to remove and replace dead and dying ash trees over the next 25 years.

The federal government has already spent millions in the past five years trying to control the spread of EAB by felling trees near known infestations. But the pest continues to spread. Last April, the USDA declared biological warfare, releasing three species of imported wasps, the EAB’s natural predator. The species are known as Oobius agrili, Tetrastichus planipennisi and Spathius agrili. When studied in China and in labs in Michigan and Massachusetts, the wasps were found to bore into the tree’s bark and lay eggs both in and on EAB’s larvae and eggs to prevent them from hatching.

“We expect the wasps will establish,” says Dr. Leah Bauer, a researcher at the Forest Service’s North Central Research Station. “They are efficient at finding their host. But we may lose a lot more trees yet. It can take five years to see any effect.”

This spring, the Forest Service took samples of trees from the five release sites in Michigan and brought the EAB egg sacks back to the lab to watch for the wasp’s establishment. “They’re easy keepers,” says Bauer. “We feed them water and honey. To get them to lay eggs, we have to dissect a branch and find the right temperature, humidity and lighting.” So far, Spathius has been seen on the larvae and Oobius and Tetrastichus are expected to follow.

As part of a five-year plan of the USDA Animal and Plant Health Inspection Service (APHIS), a new lab is being established in Michigan in a cooperative effort with the Forest Service, which will be responsible for the breeding and scheduled releases of the wasps, says Sharon Lucik, public affairs specialist for APHIS.

“Public comments on this were all over the broad spectrum—somevery much in favor, others concerned it would cause more problems,” says Lucik.

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.