Invasion of the Emerald Ash Borer

Closeup of an adult Emerald Ash Borer. Adults typically have a body with varying shades of green & purple and are half an inch long. 5 Image taken by David Cappaert of MSU

If you or someone you know has an Ash Tree (Fraxinus) on their property, then you may have heard about the insect known as the Emerald Ash Borer (EAB) beetle, which has become one of the most destructive forest species to have ever invaded the United States.

 

 

 

Background

The larval state are where the beetle is at its most dangerous.5 Image courtesy of David Cappaert of MSU

 

The EAB (Agrilus planipennis) are named as such due to their attraction to the compounds given off by ash trees and subsequent brutal breeding methods. A beetle typically has a one-year life cycle, which begins with an adult finding a host tree using a combination of sight and the scent given off by ash leaves, back, and wood. After feeding on ash leaves for a 2-3 week period, female borers lay approximately 30-200 cream-colored eggs in the crevices that lie between the layers of inner bark.2

The feeding causes “S”-shaped galleries to appear which damage the tree.4 Image courtesy of the USDA

 

Once they hatch after about a week’s time (typically in mid-summer), the larvae live within the phloem & cambium layers of the tree’s inner bark, and feed on them using trails that the larvae.2 The larvae continue feeding throughout the rest of summer and into early fall where they then lie dormant during wintertime in pupal chambers, emerging as adults in the spring, with the process continuing the following year. All in all, EAB spend approximately 3-5 weeks of their total life cycle as adults.

A good indicator for knowing if your Ash tree is infected is seeing a D-shaped hole left by the emergence.Image courtesy of David McKay of the USDA.

 

 

 

 

 

Example of bark loss damage done to Ash tree

 

 

 

Now, having a couple of larvae and adult beetles feeding on some branches or the trunk may not harm the tree at first. However, as the density of larvae continues to increase, the stress on the tree increases as well. The larvea’s feeding interrupts the tree’s ability to properly transport nutrients and water throughout its system. The resulting disconnection of nutrients produces stress on the ash tree resulting in their leaves beginning to turn yellow and fall off.2 The loss of leaves causes dieback in the tree’s canopy. As if this wasn’t enough, further damage is caused from woodpeckers who feed on the larvae that reside in the tree, pecking away at the bark, resulting in bark loss.2 After a length of time having to be subjected to this repeated cycle of being eaten from both the inside and outside, the tree is eventually too weak to support itself and dies.

 

Emerald Ash Borer in North America

In North America, the EAB have been able to infest all 16 known species of Ash tree. The first sighting of the Emerald Ash Borer in the United States was in southeastern Michigan near Detroit in 2002. Since the initial discovery, the EAB infestation has spread across over half of the American states and five Canadian provinces.1 Scientists believe that the insect came to the U.S. via contaminated solid ash wood packing material carried on cargo ships or airplanes in the 1990s from EAB-native Asian countries such as China, Japan, Russia, and Korea.2 In their native land, the EAB only colonize dying Asian ash trees, acting as a sort of secondary pest/decomposed where they aren’t causing any real harm. However, as a result of their accidental transportation to North America, ash trees who have not yet developed a defense against the insect are unable to resist and are killed, whether sick or healthy.

 

Map of the areas populated by EAB as of June 1, 2019. Presence of insect in Ohio was first confirmed on February 28, 2003 in Toledo. Image obtained from Emerald Ash Borer Information Network.1

 

Impact of EAB both economically & ecologically

Economically: The Emerald Ash Borer has been responsible for the destruction of approximately 150-200 million ash trees in the United States and the number keeps climbing. As of last count, Ohio has over 3.8 billion vulnerable ash trees with all counties being under federal regulation for EAB. The destruction of ash trees costs “municipalities, property owners, nursery operators and forest products industries hundreds of millions of dollars” as they are a valuable resource.1 According to USDA Forest Service (FS) projections, the response to the EAB infestation between 2009 and 2019 could cost up to $10.7 billion.3 This estimate includes treatment, removal, and replacement of more than 17 million ash trees in order to restore the tree’s place in the national forest ecosystem.

Ecological: The different species of ash trees each play a major role in the succession of forest ecosystems and as such the increase in mortality rates from the EAB could have a major negative impact. For example, the most widely distributed species of ash, Green, grows along rivers and streams which help prevent erosion of the soil in case of flooding. Whit ash often grows along hardwood trees such as oaks and maples in mixed stands during succession, mainly in the mid-stages.2 Black ash are typically the only trees present in the areas that they grow in (swamps & bogs of northern U.S.) and are also the most susceptible to death from EAB infestation. Although, the full impact of the increase in ash tree mortality is not known yet, there is no doubt that the loss of ash trees will distrust forest functions such as: wildlife habitats, cycling of nutrients, composition, & water movement.2

 

Methods of Combating the Infestation

One of the main reasons why invasive species are a problem is due to the fact that they have no natural predators to control population size, so their numbers increase exponentially. As such, scientists from both the Agricultural Research Service & the Animal and Plant Health Inspection Service (APHIS) began testing out an aggressive solution to the EAB infestation when first detected, the introduction of predators as biological control.3 During a search for EAB-specific predators in Asia, they found in China three parasitic wasp species that could help reduce the insect’s numbers: the first, Oobius agrili attacks EAB eggs while the other two, Tetrastichus planipennisi Spathius agrili, parasitize EAB larvae.3

The tiny wasp, T. planipennisi, is one of the predator wasps used in the study.3 Image courtesy of the USDA.

This parasitic wasp species attacks EAB larvae, which will greatly decrease mortality rates of ash trees.

 

The APHIS approved release off the three parasitic wasps species back in 2007 and they have now been released into 22 states including Ohio. Initial results from a 7-year field study have shown positive results from utilization of this approach as a severe reduction of EAB numbers was observed in the areas where the wasps were released, in some places up to 90%!.3

However as this is still a fairly recent development, studies are still ongoing to determine the true effectiveness of using parasitic wasps. So in the meantime we need to take  measures in ensuring the reduction of the spread of the infestation:

1) First and foremost absolutely do NOT move any firewood procured from infected ash trees, as this will increase the likelihood of the infestation spreading. In fact, since Ohio is under federal regulation, the “movement of hardwood firewood and wood products is under regulated and prohibited in most, but not all, circumstances” in order to limit the spread of the pests.4,This means that if you buy or sell firewood from established infected areas here in Ohio, you are prohibited from transporting it to an uninfested area whether instate or out of state.

2) A secondary method that has proven efficient is to perform a deep trunk injection.7 Simply spraying an ash tree with insecticides won’t do much as they will only be able to get the beetles that are on the outside munching on leaves rather than the larvae slowly eating away at the inside. An injection however, will ensure that the insecticide is able to impact the larvae or even prevent EAB larvae from infesting in the first place.

 

Deep Trunk Injection Explanation [1:30-2:14]7

 

Detecting the Signs

Just recently the Ash Tree in my own front yard had to be cut down due to being too sick and injured from Emerald Ash Borer infestation over a prolonged period of time. In order for the same to not happen to the ash trees in your property or at your local forests, it is important to recognize the signs that come with an EAB infestation.

Here are a couple visual real-world examples of ways to detect if you have an EAB infestation in your ash tree based off of the one from my home, such as:

 

The iconic “Bald Spot”. The deprivation of nutrients causes either a delayed growth of leaves during spring time or spots on trees will just have no leaf growth at all.

 

Notice the outer layer of bark has been stripped away, most likely due to woodpeckers feeding from the EAB larvae inside the tree. The pecking reveals the lighter inner bark underneath.

 

A branch had to cut down as it was too badly damaged.

 

 

Stressed ash trees tend to create shoots near its base or wherever it can as a form of regeneration.

 

The Emerald Ash Borer has caused serious damage to trees not just in Ohio but all across the eastern United States. Being able to detect the signs early will ensure proper treatment of the tree and prevent it from having to be cut down as mine had to be. Again, if you or some you know has an ash tree on personal property, make sure that it is not infested with EAB. There are many factors that are impacted by the infestation and it is important to stay vigilante and cautious when dealing with not only the Emerald Ash Borer beetle, but any invasive species.

 

 

Sources:

1. Matsoukis. (n.d.). Emerald Ash Borer Information Network. Retrieved June 12, 2019, from http://www.emeraldashborer.info/

2. McCullough, D. (2013, Winter). “Will We Kiss Our Ash Goodbye?” Retrieved from https://www.americanforests.org/magazine/article/will-we-kiss-our-ash-goodbye/

3. United States Department of Agriculture . (2016, May). “Tiny Wasps May Rescue Ash Trees.” Retrieved from https://agresearchmag.ars.usda.gov/2016/may/wasps/#printdiv

4. USDA Forest Service. “The Threat of the Emerald Ash Borer.”. Retrieved from https://www.fs.usda.gov/detail/wayne/notices/?cid=FSM9_005967

5. Michigan.gov. “You are hereInvasive Species Species Profiles & Reporting Information Insects.”  Retrieved from https://www.michigan.gov/invasives/0,5664,7-324-68002_71241-368696–,00.html

6. The Nature Conservancy. (2018, February 7). “Ohio Firewood Summary.” Retrieved from https://www.dontmovefirewood.org/map/ohio/

7. Arbor Experts.  (2017, September 01). Retrieved June 12, 2019, from https://m.youtube.com/watch?v=xYkAKNBX8bk

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