Introductions continue apace.
Over the past 30 years, approximately 50 new pests have been detected on the Continent and islands. These include
* At least 30 non-native species of wood- or bark-boring insects (Scolytinae / Scolytidae)[ii],[iii] – including the highly damaging redbay ambrosia beetle, polyphagous shot hole borer, Kuroshio shot hole borer.
* Eight Cerambycids such as Asian longhorned beetle;[iv]
* Seven Agrilus, including emerald ash borer and soapberry borer, to which I add the goldspotted oak borer which has been transported from Arizona to California.[v] and R. Haack, pers. comm.
* Sirex woodwasp;
* Pests of palm trees, e.g., red palm mite, red palm weevil, South American palm weevil;
* Spotted lanternfly; and
* Beech leaf disease.
In addition, pests on America’s Pacific Islands:
* ‘Ohi‘a rust;
* Cycad scale;
* Cycad blue butterfly;
* Erythrina gall wasp;
* Two Ceratocystis pathogens that cause rapid ‘ōhi‘a death; and
* Coconut rhinoceros beetle
To prevent introduction of the Asian gypsy moth, authorities have carried out approximately 25 eradication programs targetting introductions of the pest[vi] (plus pers. comm.).
[i] Guo, Q., S. Fei, K.M. Potter, A.M. Liebhold, and J. Wenf. 2019. Tree diversity regulates forest pest invasion. Proceedings of the National Academy of Sciences of the United States of America. www.pnas.org/cgi/doi/10.1073/pnas.1821039116
[ii] Haack, R.A. and R.J. Rabaglia. 2013. Exotic Bark and Ambrosia Beetles in the USA: Potential and Current Invaders. CAB International 2013. Potential Invasive Pests of Agricultural Crops (ed. J. Peña)
[iii] Haack, R.A. and R.J. Rabaglia. 2013. Exotic Bark and Ambrosia Beetles in the USA: Potential and Current Invaders. CAB International 2013. Potential Invasive Pests of Agricultural Crops (ed. J. Peña)
[iv] Wu,Y., N.F. Trepanowski, J.J. Molongoski, P.F. Reagel, S.W. Lingafelter, H. Nadel1, S.W. Myers & A.M. Ray. 2017. Identification of wood-boring beetles (Cerambycidae and Buprestidae) intercepted in trade-associated solid wood packaging material using DNA barcoding and morphology Scientific Reports 7:40316
[v] Digirolomo, M.F., E. Jendek, V.V. Grebennikov, O. Nakladal. 2019. First North American record of an unnamed West Palaearctic Agrilus (Coleoptera: Buprestidae) infesting European beech (Fagus sylvatica) in New York City, USA. European Journal of Entomology. Eur. J. Entomol. 116: 244-252, 2019
[vi] United States Department of Agriculture, Animal and Plant Health Inspection Service. 2014. Asian gypsy moth pest alert and pers. comm.
Photo of wood packaging from which beetle larvae was extracted; used with permission of Oregon Department of Agriculture
Many pests spread naturally, by flying or floating on the wind or attaching to migratory birds. Examples include gyspy moths, chestnut blight, and hemlock woolly adelgid.
Many pests have been spread from one state or region to another on ornamental plants moving in interstate trade. A recent example is the sudden oak death pathogen; in spring 2019, plants potentially infested by this pathogen were shipped to retail outlets in 18 states.
Other pests, especially wood-borers, are easily spread in firewood – both commercial shipments and individuals taking firewood from dead or dying trees from their own properties.
There are also examples of pests being spread by woodturners and wood workers who take home logs for carving. Two examples are redbay ambrosia beetle and walnut twig beetle/thousand cankers disease.
For more information about individual pests mentioned below, visit www.dontmovefirewood.org and click on “Invasive Species”.
Non-native pests have nearly eliminated some tree and shrub species and put others under severe threat. Some of these threatened species are widespread (e.g., chestnut, ‘ōhi‘a), others create unique biological communities (e.g., whitebark pine, eastern hemlock, swamp bay); others have always been uncommon (e.g., butternut).
In the eastern deciduous forest, many if not most tree species are depleted or under threat, including ash, butternut, chestnut, dogwoods, elms, hemlocks, maples, and oaks. The cumulative environmental and economic impacts have not been calculated.
Severe depletion of tree species damages the wider environment by, inter alia, depriving invertebrates and vertebrates of sources of food and shelter, altering leaf litter depth and litter and soil chemistry, changing water infiltration rates, and opening gaps that can be invaded by invasive plants.
If one focuses on economics, the highest costs arise from cities’ efforts to manage their dead and dying trees. Local governments across the country spend an estimated $1.7 billion each year to remove trees killed by the emerald ash borer or other pests. Homeowners spend an additional $1 billion to remove and replace trees. In addition, they lose $1.5 billion per year in value of their property.[i] These amounts will rise substantially as pests continue to spread.
[i] Aukema, J.E., B. Leung, K. Kovacs, C. Chivers, K. O. Britton, J. Englin, S.J. Frankel, R. G. Haight, T. P. Holmes, A. Liebhold, D.G. McCullough, B. Von Holle.. 2011. Economic Impacts of Non-Native Forest Insects in the Continental United States PLoS One September 2011 (Volume 6 Issue 9)
The most recent attempt to set priorities for conservation efforts[i] lists the following 15 tree species as most in need of protection. I have named the principal threat:
Florida torreya (Torreya taxifolia) – pathogen (a newly described Fursarium);
American chestnut (Castanea dentata) – exotic pathogen;
Allegheny chinquapin (C. pumila) – exotic pathogen;
Ozark chinquapin (C. pumila var. ozarkensis) – exotic pathogen;
Redbay (Persea borbonia) – exotic disease complex;
Carolina ash (Fraxinus caroliniana) – exotic insect;
Pumpkin ash (F. profunda) – exotic insect;
Carolina hemlock (Tsuga caroliniana) – exotic insect;
Port-Orford cedar (Chamaecyparis lawsoniana) – exotic pathogen;
Tanoak (Notholithocarpus densiflorus) – exotic pathogen;
Butternut (Juglans cinerea) – exotic pathogen;
Eastern hemlock (Tsuga canadensis) – exotic insect;
White ash (Fraxinus americana) – exotic insect;
Black ash (F. nigra) – exotic insect; and
Green ash (F. pennsylvanica) – exotic insect.
That same effort is under way for Hawai`i and the U.S. Caribbean islands. So far, it is clear that Hawai`i’s most widespread tree, ‘ōhi‘a, is under dire threat from at least two pathogens.
[i] Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S. 2019. Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/
Map updated from that published in Liebhold, A.M., D.G. McCullough, L.M. Blackburn, S.J. Frankel, B. Von Holle, J.E. Aukema. 2013. A highly aggregated geographical distribution of forest pest invasions in the USA. Diversity and Distributions. (2013) 1-9
Since European settlement began in North America, nearly 500 non-native tree-feeding insects and disease-causing pathogens have been introduced into the United States. As the map illustrates, the highest numbers are in the Northeast, upper Midwest, and Mid-Atlantic. However, the Pacific Coast states are catching up. And every county has at least three damaging non-native pests. Other damaging pests have been introduced to U.S. islands in the Pacific and Caribbean.
Photo of ash tree killed by emerald ash borer which has fallen on a house in Ann Arbor, MI; used with permission of former Mayor Hieftje
The insects and plant pathogens that are killing North America’s trees reach here primarily as larvae or spores riding undetected in several kinds of imports:
* Crates, pallets, and other kinds of packaging made of wood. Examples include Asian longhorned beetle, emerald ash borer, redbay ambrosia beetle; and
* Living plants imported for our use, often as ornamentals in our gardens. Examples include hemlock woolly adelgid, sudden oak death pathogen, and probably beech leaf disease.
Less commonly, such pests arrive on ship superstructures and hard-sided cargo (including shipping containers), in decorative items made of wood, and even on metal and stone imports (separate from any packaging). An example in the first group is the Asian gypsy moth; and example in the last group is the spotted lanternfly.