Efforts are underway in north Louisiana to slow the spread of an invasive species that threatens to destroy native ash trees. The trees play an important part in bottomland ecosystems and also have an economic value to the timber industry.
“The emerald ash borer was detected for the first time in northern Louisiana in February 2015,” said Rodrigo Diaz, LSU AgCenter entomologist. “It is a beetle native to China that has decimated ash trees in the northeastern United States within the last 15 years and has been spreading and moving south.”
Diaz stated the emerald ash borer kills ash trees by digging tunnels below the bark, cutting the flow of sap throughout the tree. Over time, all the galleries that the larvae form below the bark will reduce the flow of nutrients, he said. As quickly as six to seven years after the initial infestation the tree will die.
According to Wood Johnson, an entomologist with the U.S. Forest Service, emerald ash borer adults have been collected in Claiborne, Bossier and Webster parishes. It has only been found in trees within Webster Parish.
Johnson said it is believed that the borers disperse up to half mile per year on their own. However, others say it may travel up to 10 to 15 miles per year.
The LSU AgCenter, the U.S. Forest Service, the Louisiana Department of Agriculture and Forestry, and the Animal and the USDA’s Plant Health Inspection Service have collaborated to get a biocontrol effort off the ground in north Louisiana.
Several species of wasps native to Asia are parasites of the borer. Scientists brought the wasps to a quarantine facility in the United States to begin a rearing colony in the early 2000s. After several studies, they selected the ones that only attack the emerald ash borers.
“We obtained a release permit for the parasitoids from the USDA to use as a tool to manage the emerald ash borer,” Diaz said.
“The wasps were first released beginning in 2007 in Brighton, Michigan, and have been released in at least 18 states with Louisiana being the latest,” Johnson said.
“We are releasing an egg parasitoid that targets the emerald ash borer at two different sites in Webster Parish, near Shongaloo and near Minden,” Johnson said. “While it will not stop the spread, it should aid in slowing down the beetle.”
The entomologists released three species of wasps at the two sites. One attacks the eggs, and two attack the larvae of the borer.
“In a few weeks we will collect bark samples and remove the emerald ash borer larvae to see if the parasitoids are within the larvae and if we are having any impact on the emerald ash borer population,” Diaz said.
A second approach is to bring bolts of ash infested with emerald ash borer and leave them at the site for two weeks, with hopes that the parasitoids will attack the larvae in the bolts.
“Three to four weeks later, we will take the bolts back to the lab to see if we see emergence of the parasitoids we are releasing today,” Diaz said.
Warmer temperatures and longer growing seasons in southern climates may increase the population growth of the borer.
Much of the information on the insect comes from research conducted primarily in northern climates. By monitoring the borer and the parasitoid wasps in north Louisiana, the entomologists hope to learn more about both the borers and the wasps in the South.
Johnson indicated scientists believe the wasps could have a greater impact in the South because emerald ash borer populations have only recently become established.