An Inside Job: The Threat of the Emerald Ash Borer

It is hard to believe that something seemingly insignificant, like a beetle, could kill a fully grown tree. Typically, the main culprit of tree destruction is humans and natural phenomena, like lightning. However, there is a bullet-shaped, strikingly metallic beetle whose larvae are taking down ash trees from the inside: The Emerald Ash Borer (EAB). 

First discovered in Missouri in 2008, these invasive beetles were never meant to be in the United States. According to Collin Wamsley, a state entomologist for the Missouri Department of Agriculture, EAB are native to Asia where ash trees have natural defenses against the larvae and are unaffected by their presence. In the U.S., however, the ash trees never developed an immunity to the larvae, which allowed the beetles to tear through native forests. Found in 35 states, the beetles’ larvae feed on the inner bark of ash trees and essentially choke it from accessing water and nutrients. 

The larvae of the verdant green beetle have killed more than 50 million ash trees in the northern U.S., according to Missouri State Parks. The same study also found that in Missouri alone, ash trees make up around 14% of trees that line the streets in communities as well as over 21% of the trees in urban parks. Wamsley and Kevin Rice, an assistant professor in the Division of Plant Sciences at the University of Missouri, explain that ash trees are also commonly used to make baseball bats and furniture. Not only are EAB taking away a great economic commodity, but they are also depriving communities of beautiful landscapes. If this destruction continues at this rate, it could contribute to there being less space for native species and more opportunities for invasive species. 

When trees die rapidly in a concentrated area, they leave gaps in the canopy, which allows sunlight to hit the ground directly. This encourages invasive species’ populations to explode, Rice explained. The excess light can kill native plants that are not used to the harsh rays and provide a space for invasives to take over and outgrow native plants and trees. Some existing toxic plants can become even more toxic when exposed to excessive light, which can cause plants to grow more slowly and therefore become more vulnerable. 

Fighting to minimize the harm of these beetles is difficult, but not impossible. People are taking action to help suppress and even kill off these invasive pests. This manifests in the quarantine of lumber found in infestation sites, biological practices and the work of people like Kevin Grieb, a graduate student at the University of Missouri, who does field work at infestation sites, for example, setting up traps to contain the beetles.

Kevin Grieb gently peels wood from EAB infestation sites to look for evidence of the larvae. The larvae does not go very far into the bark, so Grieb has to be careful to not peel the bark too deep, so as to miss the galleries, or crevices, left by the larvae. Kit Wiberg/Missouri Information Corps
Samples of bark from trees that are known to be infected by EAB in Missouri sit in a cooler. According to Dr. Rice, 30-70% of trees in forests throughout the U.S. are ash trees. EAB pose a major threat to these forests because of the large population of ash trees. Kit Wiberg/Missouri Information Corps
One form of a trap for EAB sit on a table. The white portion of the trap holds anti-freeze, which kills the EAB. The green portion hangs from ash trees and expands into multiple funnels, which captures the EAB and causes them to descend into the anti-freeze. Kit Wiberg/Missouri Information Corps
Grieb uses a fine blade to peel back very thin layers of ash tree bark from samples. EAB are one of the most destructive species to ash trees. Because they are not native to the U.S., they take away a major food source from natives and leave destruction in their wake. Kit Wiberg/Missouri Information Corps
Galleries left by EAB are visible after Grieb has peeled back the exterior of the bark. The galleries often show up in a “S” formation. According to Wamsley and Dr. Rice, EAB are also one of the most expensive invasive species. It can cost hundred of dollars to properly remove an infected ash tree. If not removed, the tree could topple over and damage anything in the surrounding area. Kit Wiberg/Missouri Information Corps
As he peels the ash wood, Grieb takes notes on whether or not EAB is present in the wood, the condition of the EAB, if there are visible galleries and if there was parasitical. Another way of suppressing EAB is by quarantining lumber and wood where EAB has been sighted. According to Wamsley, in Missouri quarantines occur by county. The lumber is not allowed to leave the county until it is properly treated. Wamsley also stated that one of the easiest pathways for EAB to travel is through firewood. He suggests that people buy firewood near their destination instead of traveling with their own to prevent possible unknown travel of EAB. Kit Wiberg/Missouri Information Corps
Grieb inspects an ash tree sample, looking for the larvae in the wood. Wamsley stated that as part of biological control for EAB, three types of parasitic wasps are released into infestation sites to kill off the larvae. These wasps are very small, hardly able to be seen with a naked eye, and do not impact humans. One lab produced these wasps specifically to attack the larval stage of EAB by laying their egg inside the larvae so it hatches and kills it. Kit Wiberg/Missouri Information Corps

Kit Wiberg graduated from the Missouri School of Journalism in May 2021 with a bachelor’s degree in journalism – photojournalism.

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