The Emerald Ash Borer

An exclusive Chief River Nursery interview about the Emerald Ash Borer (EAB) with prominent Research Entomologist Dr. Robert Haack

The importance of diversification in your forest or woodlot

Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org

Photo: Pennsylvania Department of Conservation and Natural Resources – Forestry Archive, Bugwood.org

We have seen both native and exotic, or non-native, forest insects and diseases take an extreme toll on certain species of trees.  The popular ones that come to mind are the Chestnut Blight fungus and the near total loss of American chestnut, the Asian Longhorned Beetle and its strong preference for maples , and the Smaller European Elm Bark Beetle and its associated fungus that cause Dutch Elm Disease.  These pests have proven to be very destructive in nature and have led to the loss of tens of millions of trees in the United States.

Today, we are discussing another destructive exotic pest called the Emerald Ash Borer, or EAB.  We sat down with Dr. Robert Haack, a Research Entomologist with the USDA Forest Service.  Dr. Haack works out of the Northern Research Station in East Lansing, Michigan.  He was kind enough to answer some questions relating to the EAB and help us understand the importance of plant diversification on your property.

 

Interview

Q.  First of all Dr. Haack, please tell us a little bit about yourself and how you got into the field of Entomology.

I grew up in Wisconsin, in Wauwatosa, and always had an interest in the natural world, including insects.  As an undergraduate at UW-Madison in Forestry in the mid-1970s, I took two entomology courses and really enjoyed them.  I then became a Peace Corps Volunteer in Guatemala during 1975-1978, working as a forester.  During that time there was a large outbreak of pine bark beetles in Guatemala, killing millions of trees.  Seeing how destructive insects can be made me want to study them in more detail and learn ways to manage them.  So after returning to the United States I earned an M.S. (UW-Madison) and Ph.D. in forest entomology (University of Florida).  After graduating in 1984, I took a term position at Michigan State University in entomology for 2 years and then was hired full-time by the U.S. Forest Service in 1986, working as a Research Entomologist.  I work in the Northern Research Station of the US Forest Service.  Our particular Insect Research Unit is located on the Michigan State University campus in East Lansing, MI.  After joining the Forest Service, I first conducted research on how environmental stresses like drought make trees susceptible to insect attack.  But in 1992, an exotic bark beetle from Eurasia, known as the Pine Shoot Beetle (PSB), was discovered in Ohio, and within weeks in several surrounding states.  I soon started working on PSB, and then other newly discovered exotics, such as the Asian Longhorned Beetle (ALB) and Emerald Ash Borer (EAB).  Currently much of my work is focused on heat treatment protocols for wood packaging materials used in international trade such as pallets and crating.  It is likely through this pathway that most of the exotic wood borers entered our country.

For further reading, see:

Haack RA. 2006. Exotic bark- and wood-boring Coleoptera in the United States: recent establishments and interceptions. Canadian Journal of Forest Research 36: 269-288.  http://www.treesearch.fs.fed.us/pubs/18483

Haack RA, Petrice TR. 2009. Bark- and wood-borer colonization of logs and lumber after heat treatment to ISPM 15 specifications: the role of residual bark. Journal of Economic Entomology 102: 1075-1084.  http://www.treesearch.fs.fed.us/pubs/17213

Haack RA, Poland TM. 2001. Evolving management strategies for a recently discovered exotic forest pest: the pine shoot beetle, Tomicus piniperda (Coleoptera). Biological Invasions 3: 307-322.  http://www.treesearch.fs.fed.us/pubs/11857

Haack RA, Law KR, Mastro VC, Ossenbruggen HS, Raimo BJ. 1997. New York’s battle with the Asian long-horned beetle. Journal of Forestry 95(12): 11-15.  http://www.treesearch.fs.fed.us/pubs/11859

Mattson WJ, Haack RA. 1987. The role of drought in outbreaks of plant-eating insects. BioScience 37: 110-118.  http://www.treesearch.fs.fed.us/pubs/11998

 

Emerald Ash Borer exiting an ash tree.  Notice the D-shaped holes. Photo by Debbie Miller, USDA Forest Service, Bugwood.org

Emerald Ash Borer exiting an ash tree.
Photo by Debbie Miller, USDA Forest Service, Bugwood.org

 Q.  When were you first made aware of the Emerald Ash Borer (EAB) and have you had any personal experiences with EAB in the field?

Actually, I was in China, working on an Asian Longhorned Beetle project when EAB was first discovered in the Detroit, Michigan, area in early summer 2002.  Within a few days of EAB’s discovery it was positively identified by experts as Agrilus planipennis, a beetle that is native to several East Asian countries.  EAB was soon discovered in neighboring Windsor, Ontario.  I became one of the many state, federal, and university plant protection specialists who started to work on EAB in 2002, and many of us still work on EAB today.  I have been involved in many EAB research projects over the past decade, and am currently working with others on relatives of EAB in Asia that could threaten our urban and forest trees if introduced into North America.

Also, before we discuss EAB in too much detail, consider that EAB is a member of the beetle genus Agrilus.  This is a huge genus, probably the largest in the Animal Kingdom, with more than 3000 species worldwide.  There are over 170 species of Agrilus that are native to North America.  Agrilus feed primarily on woody vines, shrubs, and trees.  In general, they feed on hardwood trees (dicots), not conifers.  Most native Agrilus cause little damage, infesting recently dead or dying plants.  But during periods of environmental stress, such as a severe drought, even some of our native species can reach outbreak levels and cause widespread tree mortality, e.g., the Twolined Chestnut Borer (Agrilus bilineatus) on oaks and the Bronze Birch Borer (Agrilus anxius) on birch.  When rainfall is plentiful, populations of our native Agrilus are very low.  Interestingly, EAB is able to attack and kill both healthy and stressed North American and European ash trees, but usually only stressed Asian ash trees.

For further reading, see:

Haack RA, Jendek E, Liu H, Marchant KR, Petrice TR, Poland TM, Ye H. 2002. The emerald ash borer: a new exotic pest in North America. Newsletter of the Michigan Entomological Society 47(3-4): 1-5.  http://www.treesearch.fs.fed.us/pubs/11858

Haack RA, Acciavatti RE.  1992.  Twolined chestnut borer.  USDA Forest Insect & Disease Leaflet 168. 12 pp.  http://www.treesearch.fs.fed.us/pubs/10978

Liu H, Bauer LS, Gao R, Zhao T, Petrice TR, Haack RA. 2003. Exploratory survey for emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae) and its natural enemies in China. The Great Lakes Entomologist 36: 191-204.  http://www.treesearch.fs.fed.us/pubs/14553

 

Q.  How and when was the EAB discovered in the US?

EAB was first discovered in the Detroit area in 2002.  However, ash trees had been declining in the area for a number of years before then, and the local thinking was that the trees were dying from a disease known as “Ash Yellows.”  But in 2002, adult beetles were recovered from dying ash and subsequently identified.  Interestingly, positive identification was not that simple.  The first beetles were sent to Michigan State University (MSU) in East Lansing in June 2002.  There were no similar beetles in the MSU insect collection and so they were suspected of being exotic.  From there, either actual beetles or digital images of the beetles were sent to other beetle specialists throughout the country.  They all agreed that it was an exotic species and probably of Asian origin but they were not sure of its exact identity.  Later, images and beetles were sent to Dr. Eduard Jendek in Slovakia, who is considered the world’s expert on Asian Agrilus beetles.  He tentatively identified the beetles as EAB (Agrilus planipennis) in late June based on the photos, and later in early July he confirmed that identification when he received some of the actual beetles. In neighboring Canada, beetles suspected of being EAB were first found in Windsor, Ontario, in early July 2002, and later confirmed in early August 2002.

For further reading, see:

Cappaert D, McCullough DG, Poland TM, Siegert NW. 2005. Emerald ash borer in North America: a research and regulatory challenge. American Entomologist 51: 152-165.  http://www.treesearch.fs.fed.us/pubs/13648

Haack RA, Jendek E, Liu H, Marchant KR, Petrice TR, Poland TM, Ye H. 2002. The emerald ash borer: a new exotic pest in North America. Newsletter of the Michigan Entomological Society 47(3-4): 1-5.  http://www.treesearch.fs.fed.us/pubs/11858

Poland TM, McCullough DG. 2006. Emerald ash borer: invasion of the urban forest and the threat to North America’s ash resource. Journal of Forestry 104: 118–124.  http://www.treesearch.fs.fed.us/pubs/15034

 

Q.  When EAB attacks a tree, how does it do so and what signs and symptoms do infested trees exhibit?

Edward Czerwinski, Ontario Ministry of Natural Resources, Bugwood.org

EAB larval galleries
Photo: Edward Czerwinski, Ontario Ministry of Natural Resources, Bugwood.org

The vast majority of Agrilus species, including EAB, feed as larvae between the bark and sapwood, in what is often called the cambial region.  In order to eat and grow, the larvae construct galleries that are about the width of their body.  The galleries are constructed mostly in the inner bark and outer sapwood.  These two areas are important to trees and woody plants because that is where the bulk of translocation occurs.  That is, in general, water and minerals move upward through the outer sapwood, and sugars move downward in the inner bark.  In late summer, as the larvae become full grown, they are usually thick enough to stop or slow the water and nutrient transport in the areas where they are feeding.  When larval populations are high, then enough small areas of the plant are affected so as to girdle entire branches or the entire tree.  A single gallery can be 2-3 feet long if measured as a straight line.  In autumn, the full grown larvae construct pupal cells in either the outer sapwood or outer bark.  During the following spring, the larvae transform to pupae, and then to adults.  The new generation of adult EAB emerge from trees usually between late May and July in the Great Lakes area.  Adult Agrilus beetles chew a characteristic D-shaped exit hole when they emerge.

Some of the actual signs of EAB are the larval galleries and D-shaped exit holes.  Symptoms of EAB attack would include branch dieback, bark splitting above where larvae fed the previous year, and epicormic branching along the lower trunk.  Remember, individual ash trees often die over a 2-3 year period.  EAB often infests first in the crown and then moves downward along the trunk in succeeding years.  Therefore, the first signs of attack are difficult to see, because they are often in the canopy branches.  There are many excellent resources available that show pictures of EAB signs and symptoms.

 

Q.  We know that EAB infests Ash trees, but does it affect all types of Ash trees?  Is EAB known to affect any other species of tree other than Ash?

In North America, EAB has been able to infest every species of ash tree that it has so far encountered, including blue, black, green, white and pumpkin ash.  Remember, some trees have common names that include the word “ash” but they are not true ash (genus Fraxinus), such as Mountain Ash (genus Sorbus) and Ash-leaf Maple (genus Acer).  In Asia, EAB is known to be a pest of Ash, but in Korea and Japan EAB has also been reported to attack species of elm (genus Ulmus), walnut (genus Juglans), and wingnut (genus Pterocayra).  Recently, these non-ash reports from Asia have been called into question.  Possibly, the beetles were misidentified, or the tree species were misidentified, or simply the adult EAB beetles were collected from the foliage or bark of the non-ash trees and thus these non-ash trees do not represent true larval hosts.  So far, EAB has only developed in ash (Fraxinus) in North America.

 

Q.  One method for controlling exotic pests is to introduce natural enemies of the pest in question.  Has any progress been made on determining the natural enemies of the Emerald Ash Borer?  What is the outlook on using this method to control the current EAB outbreak?

The Eulophid wasp is a natural enemy of the EAB Photo: David Cappaert, Michigan State University, Bugwood.org

The Eulophid wasp is a natural enemy of the EAB
Photo: David Cappaert, Michigan State University, Bugwood.org

Yes, several natural enemies of EAB have been located in Asia, especially China and Russia.  These natural enemies are very small parasitic wasps that are very specific to EAB.  Some attack the eggs of EAB and some attack the larvae.  At least three of the parasitoids from China (1 egg and 2 larval parasitoids) have been brought to the USA, studied, approved for release, reared in large numbers, released in multiple U.S. states, and have become established.  It is still too early to know what the full impact of these Asian parasitoids will have on EAB populations in the North America.  In addition, more of our native parasitoids are starting to utilize EAB as a host.  Therefore, in the future, biological control agents such as these parasitic wasps should help reduce EAB populations, but given that our native ash trees are so susceptible to EAB, these parasitoids probably cannot stop the outbreak.

For further reading, see:

Bauer LS, Liu HP, Miller DL, Gould J. 2008. Developing a classical biological control program for Agrilus planipennis (Coleoptera: Buprestidae), an invasive ash pest in North America. Newsletter of the Michigan Entomological Society 53: 38–39.  http://www.treesearch.fs.fed.us/pubs/11439

Bauer L, Gould J, Duan J, Ulyshen M. 2011. Emerald ash borer biological control. In: McManus KA, Gottschalk KW (eds). Proceedings. 21st U.S. Department of Agriculture interagency research forum on invasive species 2010; Gen. Tech. Rep. NRS-P-75. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: pp. 70-73.  http://www.treesearch.fs.fed.us/pubs/37563

Duan JJ, Bauer LS, Abell KJ, Lelito JP, Van Driesche R. 2013. Establishment and abundance of Tetrastichus planipennisi (Hymenoptera: Eulophidae) in Michigan: potential for success in classical biocontrol of the invasive emerald ash borer (Coleoptera: Buprestidae). Journal of Economic Entomology 104: 1145–1154.  http://www.treesearch.fs.fed.us/pubs/43739

 

Q.  Once EAB moves through an area, is there hope that these areas can be successfully reforested with Ash trees in the future?

This may be possible someday. When EAB first moves through an area, almost every ash tree is killed, unless they are a small seedling.  But, interestingly, there are usually a few large ash trees that are not killed.  We do know for sure if these trees were simply missed by EAB or if they have some level of resistance to EAB.  Some people refer to these trees as “lingering ash” and several are being studied to see if they are resistant to EAB.  When EAB first arrives in a new area, its population will grow quickly over the next few years as most ash trees are attacked and killed, after which the EAB population will fall, but it will probably not reach zero as long as there are some susceptible ash trees in the area.  Therefore, it would not be wise to replant with ash, especially susceptible ash species, soon after EAB has moved through a specific area.

 For further reading, see:

Koch JL, Knight K, Poland T, Carey DW, Herms DA, Mason ME. 2011. Strategies for selecting and breeding EAB-resistant ash. In: McManus KA, Gottschalk KW (eds). Proceedings. 21st U.S. Department of Agriculture interagency research forum on invasive species 2010; Gen. Tech. Rep. NRS-P-75. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: pp. 33-35.  http://www.treesearch.fs.fed.us/pubs/41561

 

Q.  We have read so much regarding the spread of EAB, primarily through moving infested firewood.  Please help us understand the ways that the EAB is spread and let us know if there is anything people can do to help slow its progress.

Remember, if a tree is infested with EAB larvae, the adults may not emerge for one to two years.  Therefore, moving ash wood products or nursery stock from EAB-infested areas to uninfested areas should be avoided. EAB can be spread in ash firewood, and people have also spread EAB in ash logs and nursery stock.  It is also possible that EAB could be moved in wood chips and wood packaging material (like pallets and crating) if constructed from EAB-infested ash trees, but this has not been documented.

For further reading, see:

Haack RA, Petrice TR, Wiedenhoeft AC. 2010. Incidence of bark- and wood-boring insects in firewood: a survey at Michigan’s Mackinac Bridge. Journal of Economic Entomology 103: 1682-1692.  http://www.treesearch.fs.fed.us/pubs/40047

Petrice TR, Haack RA. 2006. Effects of cutting date, outdoor storage conditions, and splitting on survival of Agrilus planipennis (Coleoptera: Buprestidae) in firewood logs.  Journal of Economic Entomology 99: 790-796.  http://www.treesearch.fs.fed.us/pubs/14229

Petrice TP, Haack RA. 2007. Can emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae) emerge from logs two summers after infested trees are cut? The Great Lakes Entomologist 40: 92–95.  http://www.treesearch.fs.fed.us/pubs/10460

 

Emerald Ash Borer exit hole

D-shaped exit hole.
Photo: Kenneth R. Law, USDA APHIS PPQ, Bugwood.org

Q.  If a homeowner or landowner detects an EAB-infested tree on their property, what advice might you give them for their next steps?  Is there any successful preventative measures that can be taken to treat Ash trees?

If EAB arrives in a particular location, then it is important to realize that EAB is likely also present in many neighboring areas as well.  And remember as well that it is very difficult to determine if a tree is infested until the adults have emerged and left behind their characteristic D-shaped exit holes.  Various insecticides have shown good efficacy against EAB, and therefore some property owners elect to treat their ash trees with insecticides and thereby protect them from EAB.  However, treatment can be expensive, and these insecticides often have to be reapplied every 1-3 years.  So, in general, yes, individual ash trees can be protected from EAB, but given the expense this may be possible for only selected high-value trees.  In the future, if some of our native ash trees are found to be highly resistant to EAB, then these trees could be used in future breeding programs and then insecticide treatments might not be needed.

For further reading, see:

McCullough DG, Poland TM, Anulewicz AC, Lewis P, Cappaert D. 2011. Evaluation of Agrilus planipennis (Coleoptera: Buprestidae) control provided by emamectin benzoate and two neonicotinoid insecticides, one and two seasons after treatment. Journal of Economic Entomology. 104: 1599-1612.  http://www.treesearch.fs.fed.us/pubs/40210

Poland TM, McCullough DG. 2010. SLAM: A multi-agency pilot project to SL.ow A.sh M.ortality caused by emerald ash borer in outlier sites. Newsletter of the Michigan Entomological Society. 55(1&2): 4-8.  http://www.treesearch.fs.fed.us/pubs/35023

 

Q.  At Chief River Nursery, we urge our customers to practice diversification in their forest or woodlot.  Please give us your thoughts on the importance of diversification and why you may feel it is important?

The concept of tree diversification is important for individuals as well as communities.  Realize that there are likely several species of insects that feed on every species of tree that grows in our yards, along our streets, and in our forests.  In most cases, the feeding damage caused by these insects is not life-threatening to the trees.  Many trees can lose half of their leaves without showing any loss in diameter growth.  However, when new exotic insects or diseases arrive in a country, sometimes our native trees are highly susceptible to these new pests and are easily killed.  Since we cannot predict what the next new exotic pest will be, we really do not know what tree species will next be most at risk.  Therefore diversifying the tree species planted in your yard, or along your street, is good insurance from future pests that often attack a specific type of tree.  For example, after the death of millions of American elms trees to Dutch Elm Disease in the U.S. in the 1900s, many U.S. cities replanted with various species of ash and maple, never expecting the arrival someday of EAB (which favors ash) and the Asian longhorned beetle (which favors maple).

For further reading, see:

Aukema JE, Leung B, Kovacs K, Chivers C, Britton Kerry O, Englin J, Frankel SJ, Haight RG, Holmes TP, Liebhold AM, McCullough DG, Von Holle B. 2011. Economic impacts of non-native forest insects in the Continental United States. PLoS ONE 6(9): e24587. doi:10.1371/journal.pone.0024587  http://www.treesearch.fs.fed.us/pubs/38719

Haack RA, Hérard F, Sun J, Turgeon JJ. 2010. Managing invasive populations of Asian longhorned beetle and citrus longhorned beetle: a worldwide perspective. Annual Review of Entomology 55: 521-546.  http://www.treesearch.fs.fed.us/pubs/34395

Kovacs KF, Haight RG, McCullough DG, Mercader RJ, Siegert NW, Liebhold AM (2010) Cost of potential emerald ash borer damage in U.S. communities, 2009–2019. Ecological Economics 69: 569–578.  http://www.treesearch.fs.fed.us/pubs/34370

Selected webpages on EAB:

http://www.nrs.fs.fed.us/disturbance/invasive_species/eab/

http://www.emeraldashborer.info/

http://www.aphis.usda.gov/plant_health/plant_pest_info/emerald_ash_b/

 

Thank you Dr. Haack for your time and effort in working with us to create an comprehensive and informative article on the EAB.  It has been my pleasure working with you.  You can be assured that myself and my customers applaud your efforts in the field, and give you a sincere thank you for sharing your knowledge on the EAB with us.

Sincerely,

Dean A. Koch, Chief River Nursery