Stingless wasps imported to Iowa to fight emerald ash borer

DES MOINES - Thousands of stingless wasps are being enlisted to slow the onslaught of an imported pest attacking Iowa's ash trees.

Officials with the Iowa Department of Agriculture and Land Stewardship say they are turning to stingless, parasitic wasps that are natural enemies of the emerald ash borer, a highly destructive pest of ash trees that was accidentally introduced into North America from Asia and now is present in 31 Iowa counties.

Mike Kintner, the department's EAB and gypsy moth coordinator, said the 'biocontrol” effort that will begin Thursday with the release of several thousand wasps at Whitham Woods near Fairfield will not be a 'silver bullet” to rid Iowa of the EAB infestation but the introduction of natural enemies will serve as a long-term management strategy to lessen the borer's adverse impact.

'They seek out the emerald ash borer larva and then the larva of these wasps actually will feed on the emerald ash borer so they basically become a parasite,” said Laura Jesse, an extension and outreach entomologist at Iowa State University's Plant and Insect Diagnostic Clinic.

This is the first release of the natural enemies of EAB in Iowa, which has roughly 52 million rural ash trees and 3.1 million urban ash trees, but Kintner expects additional sites may be treated with biological releases to suppress and slow the spread of the destructive insects.

Emerald ash borer was first detected in the United States in 2002 and was confirmed in Iowa's Allamakee County in 2010, prompting state officials eventually to quarantine the transport of firewood among all 99 counties as a way to contain the problem.

'We're doing all we can to help slow down the spread of this and using the parasitic wasp is one more component,” Kintner said.

Following rigorous USDA testing and research on one or more parasitic wasp species that are native to Asia, similar releases of the Asian-based borers' natural predators have been made in 23 of the 25 U.S. states where emerald ash borers have been detected, she said. The current EAB infestation in and around Fairfield in Jefferson County led to the decision to release the wasps, which are harmless to people and pets, she added.

'It helps suppress the numbers,” he said. 'It's definitely not going to eradicate or put a total halt to the spread of emerald ash borer. We know that for certain. But it's just one more thing that we can use to help slow it down.”

Jesse said there will be follow-up monitoring as the parasitoids - produced and supplied by the USDA EAB Parasitoid Rearing Facility in Brighton, Mich. - get established at the Jefferson County test site under strict federal guidelines for a newly introduced biological control agent.

'This is another non-native species and we don't want to risk any problems from them,” she said. 'They're very careful in their screening process that any biological control that they release will not jump to a different host. We certainly wouldn't want it moving to our native wood-boring beetles that are not causing a problem.”

The two species of parasitic wasps available from the USDA Animal Plant Inspection Service target the larval and egg stages of EAB, according to state officials. The tetrastichus planipennisi female wasps, which are about the size of a grain of rice, lay eggs inside EAB larvae, terminating their development into adult beetles. Oobius agrili female wasps, which are the size of a gnat, lay eggs inside EAB eggs, parasitizing them before they hatch.

More information about USDA's Emerald Ash Borer Biocontrol Program can be found at

https://www.aphis.usda.gov/publications/plant_health/2014/faq_eab_biocontrol.pdf, and more information about EAB and other pests that are threatening Iowa's tree population can be found at www.IowaTreePests.com