What Is The Emerald Ash Borer?
The Emerald Ash Borer (EAB) (Agrilus planipennis) is a bright-green, wood-boring insect that is native to Japan, Korea, Eastern Russia, and Northern China (NISIC 2021). As its name suggests, both the larvae and adults primarily feed on ash tree species (Fraxinus spp.). As of 2021, hundreds of millions of ash trees in both urban and rural areas have been lost to EAB infestations in North America alone (EABIN 2021).
Ash Borer Beetles In The U.S.
The EAB was discovered in the United States in 2002 in southeastern Michigan but since has quickly spread to 35 states and 5 Canadian provinces (EABIN 2021). It is likely that the EAB arrived in North America from solid wood packing materials used to transport manufactured goods (USFS 2016). Urban areas are thought to be a main source of infection due to a 1970s boom in landscaping with ash trees (USDA 2021).
Adults can grow to about ½ inch long and consume the leaves of the ash tree, while the larvae consume the tree from the inside out, decreasing its nutrient and water exchange abilities. The larvae are flat-headed borers, white in color, and have prominent segmentation (Arbor Day Foundation 2015). EAB mate during the warm summer months in North America. Each female lays 60-90 eggs, one at a time, in weaknesses or gaps within the bark of healthy ash trees.
When the larvae hatch, they travel through the bark, making “D-shaped” entry holes, and into the tree’s cambium. As the weather gets colder, the larvae continue their transport in an “S-shape” through the cambial tissues, damaging the vascular functions of the tree, and eventually killing it. Once spring arrives, the larvae enter their pupal stage and eventually mature into adults. Come the summer season, new adult beetles emerge through the same “D-shaped” holes that the larvae had left in the bark when they initially burrowed. The adults live for about 3 weeks and are most active during the day (USDA 2021).
Ash trees are currently the only species in the United States known to host EAB, however they also have been reported to feed on elm species in Korea and elm, walnut, and wingnut in Japan (Mastro & Reardon, 2005).
Detection and Effects
Detection of EAB infestations in ash trees is nearly impossible by the blind eye until extensive damage is already done. Signs of infestation include decreases in bark and canopy, yellowed or thinning leaves, and D-shaped holes in the bark (Persad 2016). Unfortunately, the “D-shaped” holes that are created by EAB are typically high up, leading to low visual estimates of trees effected. Additionally, EAN infected trees lose most of their canopy within 2 years of infestation and die within 3-4 years (Poland and McCullough 2006). Infestation results in nearly 99% mortality for trees.
Alternative detection methods include monitoring for features including, but not limited to; branch fractures within the upper canopy that are located closer to the union of the trunk and stem, bark cracks around the first scaffold branch union, and trees that have broken in the top of the tree canopy (Persad 2016).
In 2020, a new noninvasive method for detecting EAB was utilized to detect EAB larvae under the bark before extensive damage had occurred. Electronic noses (e-noses) can detect changes in the volatile organic compounds (VOCs) as soon as damage starts and physiological changes begin in a living organism. Once a tree is confirmed to be EAB infested, it is recommended to be marked for immediate harvest (Farmer 2020).
Effects of EAB impacts range from economic loss, ecological damage, and cultural disturbance to loss of biodiversity, thermal cover, browse and protection for many wildlife species. Economic loss through timber production is likely due to ash’s high value and preference. Cultural disturbance through widespread ash mortality may be seen as a major concern for several Native American tribes that use black ash for basket-weaving and other cultural resources. Numerous wildlife species feed on ash browse and seeds while others utilize the species for shelter and protection. Ecological damage and ecosystem shifts will be a result of ash tree mortality as widespread changes in forest composition is expected (Knight, K; Long, R: Rebbeck: J, 2007). The estimated cost of EAB infestations, including treatments, removals and replacements totaled far over $10 billion (Kovacs et al. 2010).
Management and Treatment Options
Treatment options for EAB infestations are slim, therefore strict regulations and transport prohibitions on ash wood products were imposed through federal quarantines. While some of these restrictions are still in place, others have been dropped due to inefficacy in stopping new infestations and spread. The US Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) implemented quarantines on ash wood products throughout the United States. Due to the fast spread of infection even with these quarantines in place, APHIS removed EAB regulations in January of 2021.
APHIS transitioned to a new management system with the National Plant Board in order to manage firewood movement, which was found to be the main cause of current infestation spread. Most states are still regulating the movement of ash wood products, including the use of the “Don’t Move Firewood” campaign, run by The Nature Conservancy. The campaign focuses on using local firewood versus moving firewood from state to state and educating the public through outreach.
The most promising form of treatment at this time is through chemical and biological controls. Chemical controls used against EAB include an insecticide treatment called emamectin benzoate. Poland et. al (2016) found that all EAB adults fed leaves from trees treated with emamectin benzoate died within 4 days and larval density was reduced by 99% when compared to untreated trees. Chemical treatments are favored in urban and landscaped where they are appropriate. Treating wild EAB infestations with chemical treatments is currently not recommended due to numerous environmental, social, political and economic concerns.
Biological controls use natural enemies against EAB in order to decrease their populations, and therefore, decrease spread. Four wasp species, Spathius agrili, Tetrastichus planipennisi, and Oobius agrili of China, and Spathius galinae of Russia, were found to specifically hunt and kill EAB. These species were released in the United States first in 2007 in Michigan. More than 8 million wasps have since been released in 30 states and DC, and their offspring has been observed in at least 22 states at this time. It has been documented that the wasps have killed 20-80% of EAB in ash trees up to 8 inches in diameter (USDA–APHIS/ARS/FS 2019). Because of the wide percentage range of EAB mortality by the wasps, biological control will need to be integrated into a broader pest management system in order to achieve full eradication.
Lastly, as mentioned in references to e-noses, the colonization or harvest of ash is an emerging and effective method of controlling EAB infestations. By harvesting ash stands, one is essentially eradicating all possible hosts for EAB. This method, like chemical treatments, is difficult to use widely due to environmental, economic, social and cultural differences and concerns.
What Can You Do About The Problem?
Don’t Move Firewood: Avoid transporting firewood from one area to another, especially if it’s made from ash trees. Use locally sourced firewood to prevent infestations in new areas.
Dispose of Ash Wood Properly: If you need to get rid of ash wood, follow local regulations for disposal. This often involves chipping, burning, or burying the wood on-site to kill any larvae or beetles.
Recognize Ash Borer Signs: Learn to identify the signs of ash borer infestation, such as D-shaped exit holes, serpentine galleries under the bark, and dieback in ash trees. Early detection can help prevent further spread.
Report Infestations: If you suspect ash borer infestation in your area, report it to local forestry or agriculture authorities. Timely reporting can lead to quicker response and containment efforts.
Plant Diverse Trees: Encourage tree diversity in your landscape. Avoid planting new ash trees, as they are highly susceptible to ash borer infestations. Choose other native tree species instead.
Use Certified Firewood: Purchase firewood from certified sources, which are less likely to harbor ash borers. Look for the USDA-approved heat treatment label.
Follow Quarantine Guidelines: If your area is under quarantine for ash borer, be aware of and follow all guidelines and restrictions related to the movement of wood and tree materials.
Support Insecticide Treatment: If ash trees are valuable in your landscape, consult with a certified arborist or tree care professional about insecticide treatments to protect against ash borer infestations.
Educate Others: Spread awareness about the emerald ash borer and its impact on ash trees. Encourage friends, neighbors, and community members to take preventive measures.
Practice Good Tree Care: Maintain the health of ash trees in your yard through proper watering, fertilization, and regular pruning. Healthy trees are more resistant to infestations.
By following these tips, individuals can play a crucial role in preventing the spread of the destructive emerald ash borer beetle and protecting ash trees in their communities.
Current Research and Future Outlook
There is some interesting research on the use of fungi to fight against EAB.
Arbor Day Foundation. 2015. “Emerald Ash Borer”. Available from https://www.arborday.org/trees/health/pests/emerald-ash-borer.cfm
EABIN. 2021. “Emerald Ash Borer”. Available from http://www.emeraldashborer.info/
Farmer, Sarah. 2020. “E-Noses Detect Emerald Ash Borer Larvae”. Available from https://www.srs.fs.usda.gov/compass/2020/08/06/e-noses-detect-emerald-ash-borer-larvae/
Knight KS, Long RP, and Rebbeck J. 2007. Predicting emerald ash borer-induced changes in forest tree species composition. In: Mastro, Victor; Lance, David; Reardon, Richard; Parra, Gregory, comps. Proceedings, Emerald ash borer and Asian longhorned beetle research and technology development meeting. pp. 25-26. Cincinnati, OH 29 Oct. – 2 Nov. 2006. FHTET-2007-04. Morgantown, WV: U.S. Department of Agriculture, Forest Service, Forest Health Technology Enterprise Team. Abstract.
Kovacs, Kent F.; Haight, Robert G.; McCullough, Deborah G.; Mercader, Rodrigo J.; Siegert, Nathan W.; Liebhold, Andrew M. 2010. Cost of potential emerald ash borer damage in U.S communities, 2009-2019. Ecological Economics 69: 569-578.
Mastro, V., and R. Reardon (Comps.). 2005. Emerald Ash Borer Research and Technology Development Meeting, Romulus, MI, 5-6 Oct. 2004 U.S. Department of Agriculture, Forest Service publication FHTET-2004-15, Washington, DC.
NISIC. 2021. “Emerald Ash Borer”. Available from https://www.invasivespeciesinfo.gov/terrestrial/invertebrates/emerald-ash-borer
Persad, Anand. 2016. “Here’s How to Inspect Your Trees for Emerald Ash Borer”. Available from https://entomologytoday.org/2016/03/07/heres-how-to-inspect-your-trees-for-emerald-ash-borer/
Poland, T.M., and D.G. McCullough. 2006. Emerald ash borer: invasion of the urban forest and the threat to North America’s ash resource(link is external). Journal of Forestry 104(3):118-124.
Poland, Therese M.; Ciaramitaro, Tina M.; McCullough, Deborah G. 2016. Laboratory Evaluation of the Toxicity of Systemic Insecticides to Emerald Ash Borer Larvae. Journal of Economic Entomology. doi: 10.1093/jee/tov381
USDA. 2021. “Emerald Ash Borer”. Available from https://www.aphis.usda.gov/aphis/maps/plant-health/eab-storymap
USDA–APHIS/ARS/FS. 2019. Emerald Ash Borer Biological Control Release and Recovery Guidelines. USDA–APHIS–ARS–FS, Riverdale, Maryland. 65 p
USFS. 2016. “Forest Disturbance Processes: Emerald Ash Borer”. Available from https://www.nrs.fs.fed.us/disturbance/invasive_species/eab/
Ashley Spooner is an avid outdoors-woman from Thornton, NH. She has completed all of New Hampshire’s 48 4,000 Footers, the 273-mile Long Trail in Vermont, and the 100-Mile Wilderness in Maine. Ashley has also climbed all of the 4000 footers in Maine, including Katahdin numerous times, and has spent years hiking and backpacking in environments ranging from the Arctic Circle in the Lofoten Islands of Norway to the slot canyons of Utah and Arizona. She has also spent time hiking and backpacking in Montana, Oregon, California and Colorado. She holds a Master of Natural Resources degree and Sustainable Natural Resources Management Graduate Certificate from Oregon State University and currently works in Forestry for White Mountain National Forest (USFS).