Entomology researchers in the University of Kentucky College of Agriculture, Food and Environment have received encouraging results in their fight to protect Kentucky ash trees from the emerald ash borer (EAB), an exotic wood-boring invader that kills ash trees.

During the past two growing seasons, UK forest entomologist Lynne Rieske-Kinney, her lab members, and personnel from the Kentucky Office of the State Entomologist have released three species of parasitoid wasps that may be capable of helping to stop the invasive insect.

One of the wasp species — Tetrastichus planipennisi, an introduced species that is native to China — was released years ago in Michigan to take on the EAB with encouraging results. T. planipennisi lands on tree bark and detects the chewing vibrations that EAB larvae make while feeding within a tree. The parasitoid wasp then lays its eggs in the EAB larvae, eventually killing it.

This summer, Rieske-Kinney and UK entomology graduate student Bill Davidson recovered T. planipennisi from several sites, using multiple sampling methods.

“Our approach uses lower amounts of chemicals to slow EAB development and delay tree mortality, releasing biological control agents and giving native parasites time to discover newly invading EAB populations,” Rieske-Kinney said. “Our findings suggest that the parasitoid is becoming established in the research area.”

Natives to the Rescue

In addition to the parasitoid wasps, UK forest entomology researchers found two native parasitoid groups with potential to be natural biological control agents for the borer.

“One of the groups, Atanycolus, has been recovered by researchers in northern states as well,” Rieske-Kinney said. “The other genus, Heterospilus, is a parasitoid that has never been associated with the emerald ash borer before.”

Heterospilus species are known to parasitize native wood-boring larvae, several of which are closely related to the emerald ash borer. Davidson and Rieske-Kinney recovered at least two species of Heterospilus in borer-infested logs.

“Our findings suggest that this genus may easily transition to EAB,” she said. “They also suggest that our native parasitoids may be learning the emerald ash borer is available and may be using it as a host, hopefully contributing to EAB suppression.”