Pretty is as Pretty Does: The Tale of an Emerald Insect Eating its Way Across Virginia
September 28, 2017 2:02 pm
Watch: Emerald Ash Borer: Fighting Back with Biocontrol
This video shows how The Virginia Department of Forestry (DOF) is using biological control agents—tiny parasitoid wasps from Asia—to combat the emerald ash borer threatening Virginia’s ash trees.
The emerald ash borer is an invasive insect that is native to Asia and it was first discovered in the U.S. in 2002 in Michigan and then it reached Virginia in 2008. So it’s been slowly spreading throughout the state since then and currently it’s found in over 50 Virginia counties, so that’s over half of the state. And it will infest and kill any ash tree that is native to Virginia. So today we are releasing biocontrol agents to try to prevent the spread of emerald ash borer. In addition to biological control there are also control methods for the emerald ash borer using insecticides. We’re choosing to use biological control at Cumberland State Forest because there are plentiful ash and it’s not really cost-effective for us to go out and treat every individual tree with insecticide so this is kind of a more long-term sustainable approach if you will. So a bio control agent is a predator of the pest in its natural environment. So the emerald ash borer is native to Asia and in Asia there are predators and parasitoids that control the emerald ash borer population. We don’t have those here in Virginia since the emerald ash borer is not native to Virginia, so what we’re doing is we’re releasing some of these biocontrol agents that are native to Asia here in Virginia. But all of these biocontrol agents have been tested in quarantine facilities for years prior to them being allowed to be released here. And they’ve been tested against any other possible hosts that they may come into contact so by the time that that we’re allowed to release them here we are very certain that they will not attack anything other than that emerald ash borer. We’re releasing our first biological control agent which is a Oobius wasp sp. parasitoid. So this is a tiny little wasp that is native to China and what it does is it lays eggs inside the eggs of the emerald ash borer. And then when those parasitoids eggs hatch they end up killing the emerald ash borer eggs. These wasps are in their pupae form so when they emerge from the pupae as adults they’ll fly away from the container and hopefully parasitize emerald ash borer eggs that are on this tree and surrounding trees in the area. The second biological control agent that we’re releasing out here is Tetrastichus wasp sp. and it is a larval parasitoid of the emerald ash borer so similar to when Lori was speaking about Oobius where the parasitoid will actually lay her eggs inside of the eggs, and Tetrastichus will lay her eggs inside of the larvae that are inside feeding on the ash trees. And so by releasing these releasing adults both male and female of the species and weres releasing them out there and they will sense when there are larvae inside of the tree and she will lay her eggs through into the larvae itself and her developing young will feed on and subsequently kill the emerald ash borer larvae and stop them from feeding while they’re in the tree right there. So we’ll definitely continue to monitor this site for the next few years to see if these parasitoids are able to establish a population here. And there’s a number of ways to do that; You can try to trap for the adult wasps to see if they’re still in at this site. If you have the means you can also fell a tree, debark it, find the emerald ash borer larvae, and dissect them looking for the eggs that were laid by the parasitoids. So one of those methods we’ll use to continue to monitor the site for the next few years.
“They look so pretty!” That’s what I said the first time I saw an adult emerald ash borer (EAB). But I soon learned from our DOF Forest Health team that this green insect’s destruction is anything but pretty.
EAB came to the United States from Asia, was first discovered in Northern Virginia in 2008 and is boring its way through ash trees from Michigan to Virginia. “Adult ash borers are metallic green beetles that can be seen flying around the tops of ash trees in late spring and early summer,” DOF Forest Health Manager Lori Chamberlin said. “These beetles lay eggs on ash bark, and the larvae that hatch tunnel into the tree and feed under the bark. This disrupts the flow of water and nutrients within the tree – effectively choking it to death.”
No ash tree native to Virginia is resistant to EAB, according to Chamberlin. And, unless they are treated before or very early in the infestation, all ash trees that are infested will eventually die.
Hope for Landowners
But there is an arsenal to push these invasive insects back. “We recommend either a stem injection or a soil drench,” said Chamberlin. “But the time to do this is now, because once an ash tree has lost more than 30 percent of its canopy, it’s too late to save the tree.”
Chamberlin recommends that landowners contact a certified arborist to discuss the treatment options, their costs and the timing of these treatments.
Chemical treatment is effective and most appropriate for high-value landscape trees. Unfortunately, treatment is not normally effective in a forest setting. According to forest survey data, ash makes up approximately two percent of Virginia’s forests. However, it can comprise a significant portion of individual forest stands, especially in riparian and mountainous areas. If you own forestland with a large component of commercially valuable ash, the DOF recommends discussing your forest management options with a professional forester. Options may range from conducting a silvicultural harvest to doing nothing and leaving the dying/dead trees as wildlife habitat. Check out additional information about professional consulting foresters working in the Commonwealth.
Cutting Edge Push Back
I went out this summer with Lori Chamberlin, DOF Forest Health Specialist Katlin Mooneyham and University of Virginia Forest Health Intern Kendra Counts to try out an EAB management method in Cumberland State Forest (check out the video up top). It was hot; there were mosquitoes and waist-deep poison ivy. But the work this team accomplished will go a long way towards learning how best to fight back against EAB.
As we waved off mosquitoes and navigated the underbrush, Chamberlin and Mooneyham explained that biological control is the most effective effort that we can use in controlling these beetles as they move through forested settings where other control options are not viable. The only other real shot we have at controlling EAB is use of insecticides, but in forests that is difficult because of the amount of ash present and the expense of treatment for that many trees.
“Biological control is a key tool in the integrated pest management toolbox for controlling invasive species,” said Mooneyham. “When we’re faced with a widespread attack, such as we are currently experiencing in Virginia with EAB, we need all the help we can get.”
I like to refer to this summer’s experience as “releasing the hounds,” but we actually released parasitoid wasps. Two releases occurred this summer, one in Whitney State Forest in Warrenton and one in Cumberland State Forest in Cumberland. At Whitney 600 Oobius agrilus (a species that attacks EAB eggs) and 855 Tetrastichus plannipennis (a species that attacks EAB larvae) were released. At Cumberland 400 Oobius agrilus and 403 Tetrastichus plannipennis were released. These wasps pose no threat to humans –– they don’t sting and in fact they are very tiny (really…check them out in the video!). Tetrastichus plannipennis is only 3-4 mm in size and Oobius agrilus is similarly very small.
A cardboard box in which the parasitoid wasps arrive from the USDA.
And don’t worry; they’re safe (unless you’re an EAB), legal and extensively tested. DOF received approval to release these wasps from USDA APHIS since testing in quarantine showed that they were not a threat to other native insects or animals. This also means that since the wasps are so species-specific for their prey that their population rises and falls along with changes in EAB populations!
The DOF Forest Health staff continues to monitor the establishment of these predators over the next few years at these two sites and hopefully more releases on other state lands will follow. Ultimately, the release of these parasitoids is one of the efforts DOF is pursuing to protect ash throughout Virginia and gives hope that EAB’s march through our state can be slowed.
Click here to learn more about EAB or these parasitoids.
Tags: Arborists, Ash, Emerald Ash Borer, Insects, Pest Management
Category: Forest Health