Emerald ash borer (Agrilus planipennis) or EAB has cut a wide swath of destruction across a large portion of the United States, including Illinois. EAB has been responsible for the death of tens, if not hundreds, of million ash (Fraxinus spp.) trees, which has led to drastic changes in some communities and landscapes.
Typically beetles like EAB (buprestid beetles) attack stressed or declining trees. This is what EAB does with the native ash trees in their native range (northeastern China, the Korean peninsula, and eastern Russia). Unfortunately, the North American ash species have no resistance to EAB, so the beetles are able to attack and eventually kill healthy trees. Trees may not show any symptoms of EAB (canopy thinning, increased woodpecker activity, D-shaped emergence holes, as well as s-shaped galleries and splitting bark) for a year or two, but once an ash tree ‘gets’ EAB, the trees will typically die within 2 to 6 years.
Emerald ash borer was first discovered/identified in the U.S. in Michigan in 2002. However, it is believed the beetles first arrived in the early 1990s and had begun killing trees in the Detroit area by 1998. EAB was first found in Illinois in 2006 in the Chicago area and has currently been found in 35 states.
When EAB was first discovered in the U.S. and Illinois, quarantines were enacted to try to stop and eventually slow the spread of the insect by restricting the movement of firewood and ash material, such as trees. However, in 2015, after EAB had spread to nearly 60% of the counties in the state, Illinois decided to deregulate the movement of firewood and ash material. In January 2021, the USDA also decided to end its quarantine in favor of directing its efforts to researching and releasing biological control agents to manage EAB populations.
More than 99% of ash trees that have been attacked have been killed (less than 1 in 1,000 survive). This has had massive impacts in both urban settings as well as forests.
Much of the public’s attention has been on the impact on urban settings. In a study conducted in 2011, researchers estimated it would cost between $13.4 and $26 billion to remove and replace ash trees growing in parks, private land, and along streets in communities in Illinois, Indiana, Michigan, and Wisconsin alone. These figures are just for tree removal and replacement and do not look at decreased property values.
The above numbers don’t take into account the other benefits of trees. Trees can increase property values, help decrease cooling costs, help with stormwater capture and retention, help capture air pollution, among other benefits.
Urban trees can also positively impact human health. Studies have shown that urban trees can help improve air quality and reduce the incidence of cardiovascular disease and asthma. They can help people recover faster recovery from surgery and increase residents’ physical activity. A study in 2013 found that the loss of ash trees in a 15-state area (including Illinois) correlated with an increase of more than 20,000 deaths due to respiratory and cardiovascular disease.
In addition to the major impact on our urban settings, EAB has also impacted forested areas. It is estimated that there are/were over 8 billion ash trees that were in U.S. forests. The loss of ash trees can open up forest canopies. This increase in light availability can lead to the increase of invasive species such as multiflora rose, invasive honeysuckles, and autumn olive.
The loss of ash trees also impacts animals that rely on them. Nearly 300 species of arthropods (mites and insects) feed on ash trees. A majority of these will feed on other plants, so their populations aren’t necessarily in danger. However, nearly 100 of them are dependent on ash at some point in their lives and are at risk as trees disappear. This includes 32 species of butterflies and moths, 24 species of bugs, 24 species of beetles, and nine species of flies.
While birds and mammals may not depend on ash trees, their loss can still negatively affect them. The insects that rely on ash are a food source for birds. In addition to losing a potential food source, birds also lose nesting habitat. Mammals like deer and rabbits will feed on ash foliage. Animals like squirrels, chipmunks, cardinals, chickadees, and turkeys will feed on ash seeds.
There are also economic losses associated with losing ash in forests. According to the U.S. Forest Service:
- The 8 billion ash trees in U.S. forests are worth an estimated $282 billion.
- Timber from ash trees is valued at $25 billion/year in the eastern U.S.
- This wood is used to make tool handles, baseball bats, furniture, cabinetry, basketry, solid wood packing materials, pulp, and paper.
What’s being done?
All is not lost when it comes to ash trees. Some trees, often called lingering ash, have been able to survive attacks from EAB. There are currently efforts underway to breed EAB resistant native ash trees. However, it will take years before any potential trees could be planted.
In addition to breeding efforts, a lot of work has gone into biological control of EAB. Scientists have traveled to Asia to identify natural enemies of EAB. Once discovered, these insects were brought to the U.S. and studied to make sure it would be safe to release them (they wouldn’t become invasive pests themselves).
Currently, one species of egg parasitoid (Oobius agrili) has been released. The female wasp lays its eggs in the eggs of EAB, and the wasp larva will eat the EAB egg. Three species of larval parasitoids (Tetrastichus planipennisi, Spathius agrili, and Spathius galinae) have been released. The females of these wasps will lay their eggs on the outside of EAB larva (Spathius species) or inside the EAB larva (T. planipennisi). After the wasp larva hatch, they will eat the EAB larva.
Since 2007, over 5 million parasitoid wasps have been released. Three of the wasp species have become established (O. agrili, T. planipennisi, and S. galinae) in the areas they have been released. In some areas, up to 80% of the EAB larva examined have been parasitized by these wasps. Hopefully, these parasitoids will be able to slow the spread of EAB and protect ash trees, allowing them to survive.
EAB has taught us many lessons. Here are some things you can do to try and prevent the spread and introduction of invasive species:
- The majority of the spread of EAB has been due to the movement of plant material, particularly firewood. It’s always best to buy or collect your firewood near where you will be burning it instead of bringing your own to avoid spreading insect pests and plant diseases.
- Don’t Pack a Pest. The U.S. restricts or prohibits the introduction of plant material, soil, and other agricultural products into the country without a permit.
- Make sure you are purchasing plant material from legitimate sources.
- EAB has once again shown the importance of planting a diversity of trees in our urban landscapes. In many communities, ash was widely planted because it was able to survive well in urban areas, and it was a replacement for elm trees that were killed by Dutch elm disease (caused by an invasive fungus). If you’re thinking of planting a tree, take a look around your neighborhood. If you notice a lot of one type of tree, like maple, plant something else.
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Sources and more information
Donovan, Geoffrey H., David T. Butry, Yvonne L. Michael, Jeffrey P. Prestemon, Andrew M. Liebhold, Demetrios Gatziolis, and Megan Y. Mao. “The Relationship Between Trees and Human Health: Evidence from the Spread of the Emerald Ash Borer.” American Journal of Preventive Medicine 44, no. 2 (February 2013): 139–45. https://doi.org/10.1016/j.amepre.2012.09.066.
Duan, Jian J.; Van Driesche, Roy G.; Bauer, Leah S.; Reardon, Richard; Gould, Juli; Elkinton, Joseph S. 2017. The role of biocontrol of emerald ash borer in protecting ash regeneration after invasion. FHAAST-2017-02. Morgantown, WV: U.S. Department of Agriculture, Forest Service, Forest Health Assessment and Applied Sciences Team. 10 p. [brochure]. https://www.fs.fed.us/foresthealth/technology/pdfs/FHAAST-2017-02_Biocontrol_role_EAB_regeneration.pdf
Gabriel Popkin. “Can an Ambitious Breeding Effort Save North AMERICA’S Ash Trees?” ScienceMag, November 12, 2020. https://www.sciencemag.org/news/2020/11/can-ambitious-breeding-effort-save-north-america-s-ash-trees.
Herms, Daniel A., and Deborah G. McCullough. “Emerald Ash Borer Invasion of North America: History, Biology, Ecology, Impacts, and Management.” Annual Review of Entomology 59, no. 1 (2014): 13–30. https://doi.org/10.1146/annurev-ento-011613-162051.
Klooster, Wendy S., Kamal J.K. Gandhi, Lawrence C. Long, Kayla I. Perry, Kevin B. Rice, and Daniel A. Herms. “Ecological Impacts of Emerald Ash Borer in Forests at the Epicenter of the Invasion in North America.” Forests 9, no. 5 (May 5, 2018). https://doi.org/10.3390/f9050250.
Sydnor, T. Davis; Bumgardner, Matthew; Subburayalu, Sakthi. 2011. Community ash densities and economic impact potential of emerald ash borer (Agrilus planipennis) in four midwestern states. Aboriculture & Urban Forestry. 37(2): 84-89. https://www.nrs.fs.fed.us/pubs/jrnl/2011/nrs_2011_sydnor_001.pdf
USDA–APHIS/ARS/FS. 2019. Emerald Ash Borer Biological Control Release and Recovery Guidelines. USDA–APHIS–ARS–FS, Riverdale, Maryland. https://www.nrs.fs.fed.us/disturbance/invasive_species/eab/local-resources/downloads/EAB-Biocontrol-FieldReleaseGuidelines-2019.pdf
Wagner DL, Todd KJ (2015) Ecological impacts of emerald ash borer. In: Van Driesche RG, Reardon RC (eds) Biology and control of the emerald ash borer. FHTET-2014-09. USDA Forest Service, Forest Health Technology Enterprise Team, Morgantown, pp 15–63. file:///C:/Users/kjohnso/Downloads/FHTET-2014-09_Biology_Control_EAB.pdf