FRANKFORT, Ky. — As bad as the spread of the emerald ash borer (EAB) has become, research efforts at the University of Kentucky College (UK) of Agriculture, Food and Environment are showing promise of slowing it down.

The EAB has attacked ash tree populations in 24 states and Canada so far, with no end in sight to the spread of the pest. UK forest entomologist Lynne Rieske-Kinney, members from her lab and employees 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, though.

“The ash can be protected with chemicals but, of course, that is expensive and not sustainable,” she said. “The approach that we’re trying with some success in my lab is to treat ash in affected areas at reduced rates of chemicals, which essentially will slow the mortality of the she trees and slow the development of the EAB.”

Rieske-Kinney added when that happens, the biological control agents – the parasitoids – are released into the system, allowing them to become established. “The problem with biological control in untreated stands is that the trees die so fast and the EAB then leaves because there are no trees,” she said. “If you can slow that whole process down considerably, the hope is that the parasitoids, which are natural enemies, would be able to get established.”

Slowing the process would seem key since the EAB has done extensive damage in the dozen years it has been in this country. The Michigan Department of Agriculture and Rural Development notes since the EAB was first discovered there in 2002, the insect is responsible for the death or damage of approximately 50 million ash trees in Michigan and surrounding states.

Rieske-Kinney said a good indicator the biological agents are working is the fact that all that have been released have been recovered. Once the parasitoids are released in an infested forest area, samples of that forest are taken in a variety of different ways to not only see how EAB populations are doing, but also to see if these natural enemies released can be recovered.

“Probably just as important, we’ve documented occurrences of native parasitoids that are learning to use the EAB as a resource,” she said. “There are a lot of native species of wood borers that are very closely related to EAB, and so it stands to reason that their natural enemies would also be natural enemies of the EAB if they knew they were out there.”

Unfortunately, the EAB kills its host trees so rapidly, it moves on before these native natural enemies have a chance to slow or destroy the pests. Just how long it will take to get these EAB enemies established is not completely known but it depends on a few things. “We don’t really know and it varies geographically, and it varies with the type of forest you release it in,” explained Rieske-Kinney. “I feel very lucky we got as rapid a recovery as we did.”

But just because all the parasitoids are recovered doesn’t mean they have become well established. Multiple cycles of reproduction have to take place, so one year would not be enough.

“You have to show repeated recovery of these insects in multiple life stages and we have not shown that yet,” said Rieske-Kinney. “All we have is recovery but still, that is the first step. I’m really hopeful that we do have establishment of these natural enemies in our forest.”

According to the Kentucky Division of Forestry, the state has more than 130 million white ash and 92.5 million green ash trees. The EAB was first discovered in the state in 2009 and has now spread to 35 counties. The largest number of ash trees are located in Henry, Bath, Spencer, Pulaski and Hopkins counties, with this research having been conducted in Henry, Spencer, Fayette, Anderson and Shelby counties.