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Hear about invasive species from the experts!


David Nisbet
David Nisbet
David Nisbet's Blog

Healthy community forests are important for recreation and the promotion of healthy air and lifestyles.  This is true for human wellbeing, but even small woodlots can be critical for providing excellent habitat for wildlife.  In Southern Ontario, many forest tracts are fragmented for human development and infrastructure, but still serve as refuges for wildlife including millions of migratory birds.  Municipal forest tracts and urban woodlots act as islands by providing shelter and food for species residing in the surrounding natural habitat1.  These small forests are threatened by emerald ash borer (EAB; Agrilus planipennis), an invasive boring beetle from Asia that arrived in North America in 20022.  EAB can damage and eventually kill all 16 ash (Fraxinus spp.) species in North America of any size or age including healthy trees2.  Adult female EAB lay their eggs just under the bark of ash trees3.  The damage is first seen in the upper canopy because when the eggs hatch, the larvae feed on phloem tissue which inhibit the tree’s ability to distribute nutrients to the upper branches3.  In Southern Ontario, both managed and natural woodlots may include large ash components.  EAB is already responsible for killing millions of ash trees in the USA and Canada with billions of trees at risk2.  

The canopy structure is an important criterion for returning migratory birds when choosing territory4 as a result, the tree cover in municipal forests is critical for supporting bird diversity.   The impending EAB related mortality will be important for migrating and resident bird species as forest canopy changes can influence animal biodiversity5,6 and singing behaviour7 in complex ways8.  First, the bird community may change as the forest canopy and understory characteristics change because what may be beneficial for some species will prove less attractive for others9,10.  Second, birds that remain in poor-quality habitat may sing less in the dawn chorus as a relation to their reduced condition7, inhibiting their ability to find a mate. My research will consider ecological effects of EAB infestation on songbird diversity and signalling behaviour on a community scale in York Region, Ontario forest tracts. 

Anyone who has spent time in the forest in the early morning hours of spring has heard the dawn chorus of birds.  The dawn chorus occurs is the breeding season when male songbirds produce loud, distinctive songs to attract mates and defend their chosen territory against males of the same species11.  It is a phenomenon that begins in the early morning hours, and for decades researchers have been waking up to listen to and record the dawn chorus to study the birds who live in the community.  For my research, I deploy automated recorders in Southern Ontario forests tracts with ash composition, in order to capture bird songs at the height of their signalling behaviour7.   After 48 hours, the memory cards were collected from the recorders and using bioacoustics software, I identified species in the community by their songs.  The audio recordings of these male bird songs are visualized by spectrograms (visualizations of sound frequency over time scales; Figure 1).   Too learn the members of the songbird community, I identify each species’ song once per recording.  For the black-capped chickadee (Poecile atricapillus) I’ll note each song to measure any possible differences in signaling behavior at dawn between forest tracts with more EAB related mortality.


Fig. 1 Two sample annotated spectrograms of male songs from SM2 recordings taken on May 23, 2016 in major ash composition (>30%) in the North Forest Tract in York Region, Ontario.  A) Represents 8 seconds of the dawn chorus beginning at 3:44 am.  B) Represents 8 seconds beginning one hour after the start of A.

Another interesting technology employed in my research is the unmanned aerial vehicle (UAV) or drone, I use to document canopy mortality.   EAB related canopy die-off can occur rapidly2, and my small, commercially produced, UAV is flown to capture cover images document additional canopy data, and archive any differences over time.  Multiple UAV images are stitched together to form a mosaic that fully captures the forest canopy.  We can use these composite images for an estimate of the percent canopy mortality by only selecting the dead trees (Figure 2).  This is relatively easy to do because there is a tendency for dead trees to be a different colour than the living vegetation around them12.  The pixels representing dead canopy can give a percentage of canopy mortality in each area.  


Fig. 2 A) An unmanned aerial vehicle acquired image of emerald ash borer related ash mortality in Oakville, Ontario.  B) The same image as in A, after px representing canopy mortality have been selected and filled white.  In this image, 2172885 px of the total 12000000 px denotes approximately 18.1% canopy mortality.

As a Masters of Environmental Science candidate at Nipissing University and funded by an Industrial Postsecondary Scholarship by NSERC and BioForest Technologies in Sault Ste. Marie, my research considers any possible correlation between songbird community members and canopy mortality percentages.  Additionally, for the black-capped chickadee I’ll compare the vocal performances of the dawn chorus across plots varying in ash canopy mortality.  I hope to further our understanding on the influences biological invasions impose on native songbird community structure and signalling quality.  This is especially important in the small fragmented forest tracts serving as limited habitat.  In addition, I hope that my methods to use an acoustic measure of diversity and UAV acquired imagery will help create new survey methods for assessing community changes during inevitable biological invasion events.

By Mandy Ehnes
Masters of Environmental Science candidate,
Nipissing University 
Email: mehnes14@gmail.com

REFERENCES

1.      Alvey AA. 2006. Promoting and preserving biodiversity in the urban forest. Urban For. Urban Gree. 5(4):195–201.

2.      Poland TM, McCullough DG. 2006. Emerald ash borer: invasion of the urban forest and the threat to North America’s ash resource. J For. 104(3):118-124. 

3.      Eyles A, Jones W, Riedl K, Cipollini D, Schwartz S, Chan K, Herms DA, Bonello P. 2007. Comparative phloem chemistry of Manchurian (Fraxinus mandschurica) and two North American ash species (Fraxinus Americana and Fraxinus pennsylvanica). J. Chem. Ecol. 33(7):1430-1448. 

4.      Sanesi G, Padoa-Schioppa E, Lorusso L, Bottoni L, Lafortezza R. 2009. Avian ecological diversity as an indicator of urban forest functionality. Results from two case studies in northern and southern Italy. Arboriculture and Urban Forestry. 35(2):80-86. 

5.      Blumenrath S, Dabelsteen T. 2004. Degradation of great tit (Parus major) song before and after foliation: Implications for vocal communication in a deciduous forest. Behav. 141(8):935-958. 

6.      Showalter CR, Whitmore RC. 2002. The effect of gypsy moth defoliation on cavity-nesting bird communities. Forest Science. 48(2):273-281. 

7.      Ingebjorg JK, Otter KA, Van Oort H, Holschuh CI. 2005. Communication breakdown? Habitat influences on black-capped chickadees dawn choruses. Acta. Ethol. 8(2):111-120. 

8.      Drapeau P, Leduc A, Giroux J, Savard JL, Bergeron Y, Vickery WL. 2000. Landscape-scale disturbances and changes in bird communities of boreal mixed-wood forests. Ecol. Monogr. 70(3):423-444.

9.      Candolin U, Voigt HR. 2001. Correlation between male size and territory quality: consequence of male competition or predation susceptibility? Oikos. 96(2):225-230.

10.  Tingley MW, Orwig DA, Field R, Motzkin G. 2003. Avian response to removal of a forest dominant: consequences of hemlock woolly adelgid infestations. J. Biogeogr. 29(10-11):1505-1516.

11.  Mennill DJ. 2011. Individual distinctiveness in avian vocalizations and the spatial monitoring of behaviour. Int. J. Avian Sci. 153(2):235-238.

12.  Dunford R, Michel K, Gagnage M, Piegay H, Temelo ML. 2009. Potential and constraints of unmanned aerial vehicle technology for the characterization of Mediterranean riparian forest. International Journal of Remote Sensing. 30(19):4915-4935.


Originally posted in February, 2015

In 2014, the Journal of Economic Entomology  published a paper confirming the emerald ash borer has successfully attacked fringetree (
Chionanthus virginicus) in Ohio.While this was the first incidence of EAB attacking anything other than an ash, this is not a cause for alarm. The beetle has not switched hosts, and it has not adapted to the fringetree after consuming all the available ash in an area. Rather, it is simply pre-adapted to feed on fringetree in the same way it is pre-adapted to feed on North American ash trees, even though it has never encountered any of these species before.

Ash and fringe trees are in the same family, Oleaceae family, and are the most Phyllogenetically closely related genera on the Oleacea family tree. The ash genus (Fraxinus) is most closely related to the fringetree (Chionanthus), with ash being used as rootstock for grafting fringetree. So it’s not surprising that fringetree physiology and chemistry are similar enough that the insect is able to reproduce on fringetree.




Fig. 1 Summary of the molecular phylogeny of Oleaceae ( Wallander and Albert, 2000)

Insects do not eat Latin binomials. This is a man-made classification used to categorize organisms. They eat plant material that contains the right mixture of feeding stimulants and nutrition, as well as feeding inhibitors, deterrents, and plant defenses. EAB co-evolved with its host ash species in Asia. Over millennia the Asian ash evolved chemicals and other tree responses to ward off attacks by EAB. But when the trees are weakened and stressed they can’t produce the chemical deterrents or compartmentalize the damaged tissue. EAB is able to overwhelm the tree and kill it.

The beetle arrived in North America pre-adapted to select and attack ash trees. The problem for the trees is they have not evolved the defense like their relatives in Asia. The beetle attacks and overwhelms the tree’s defenses, and kills it. In North America, the tree defenses are inadequate to protect it from EAB, and the beetle is able to attack and kill apparently healthy trees. In its evolution to attack Asian ash, EAB developed host selection behaviour and larval feeding processes based on its ability to find trees that smell, look, taste, grow, and defend themselves like Asian ash . Given their evolution, trees in the olive family (North American ash, fringe tree, lilac, etc.) are likely to have some chemistry and physiology in common with Asian ash. So it’s no surprise EAB attacks North American ash. It’s also not surprising that there might be a few species like the fringe tree which it may also attack. The Fringe tree is very closely related to ash. Ash rootstock is used for nursery production of fringe trees, so the trees must have similar physiology.


Fig. 2 EAB damage on white fringetree, 
Retrieved from http://phys.org/news/2015-07-white-fringetree-emerald-ash-borer.html

Moreover, earlier bioassays by Deborah McCullough at Michigan State University showed that EAB will colonize lilac, which is also in the olive family with ash, but in her studies EAB larvae do not survive to pupation. McCullough could not get them feed on privet, which is also in the olive family.


The situation in Ohio is not a case of EAB moving to the fringe tree after killing all the ash. It is feeding on the fringe tree while there is still lots of ash around. Its survival doesn’t appear to be as good as on ash, so fringe tree doesn’t appear to be an optimal host. It’s simply feeding on a tree species is that is a lot like ash in its chemistry, physiology, and tree defenses.


By Taylor Scarr

Director Integrated Pest Management
Great Lakes Forestry Centre


Originally posted on May 15, 2015

Early efforts to eradicate emerald ash borer (EAB) from North America in 2002 eventually ended because there were no available tools for detecting or limiting its spread and the high number of new infestations being found each year suggested that EAB was already well established in North America. Thus, biological control came to the forefront as a potential long-term strategy for combating EAB.

Early surveys for EAB natural enemies in China during 2003 identified two parasitoid wasps: Tetrastichus sp. (Hymenoptera: Eulophidae) and Spathius sp. (Hym: Braconidae), later identified to species as the larval parasitoids, Tetrastichus planipennisi Yang and Spathius agrili Yang, respectively. Research conducted showed that T. planipennisi is an endoparasitoid, laying its eggs inside EAB larvae, whereas S. agrili is an ectoparasitoid, laying its eggs on the outside of EAB larvae. Both species of wasps are known to be gregarious (i.e. producing many offspring from just a single EAB host) and capable of parasitizing up to 50% of EAB larvae in the field (Liu et al. 2003). A solitary egg parasitoid, Oobius agrili Zhang and Huang (Hym: Encyrtidae), was also found attacking EAB in China, but unlike the former parasitoids, it produces only one offspring per EAB egg. Surprisingly, O. agrili has been shown to parasitize up to 61.5% of EAB in China, its home country (Liu et al. 2007).


Figure 1. A 4th-instar emerald ash borer (EAB) larva on a cut, debarked ash tree. EAB larvae feed in serpentine galleries in the phloem and cambium, usually scoring the outer xylem; this disrupts the flow of nutrients and water, leading to ash mortality. Photo by: Justin M. Gaudon

All three Chinese parasitoid wasps were first released in North America in 2007 following tests on their host ranges and rearing potential. They continue to be released in both the USA and Canada and their establishment monitored. Currently, North American parasitism of EAB by these wasps is lower than that observed in China, likely due to their recent introduction.

Similar surveys for native natural enemies were also conducted in North America during the early years, and several species have been found to attack and parasitize EAB. Although low rates of parasitism of EAB by native parasitoids are typical, high levels have been recorded, usually associated with older, more established EAB populations. Two native species that appear to be important mortality factors of EAB include the solitary larval ectoparasitoid, Atanycolus cappaerti Marsh & Strazanac (Hym: Braconidae) and the solitary larval endoparasitoid, Phasgonophora sulcata Westwood (Hym: Chalcididae). Cappaert and McCullough (2009) reported up to 71% parasitism of EAB by A. cappaerti, while Lyons (2010) calculated a parasitism rate of 40.7% for P. sulcata based on sticky trap catches. Both show strong potential to reduce populations and slow the spread of EAB, and this has inspired me to further investigate their ability as biocontrol agents against EAB.


Figure 2. Native Atanycolus sp. released into a Toronto field site by transporting ash logs cut from sites heavily infested by emerald ash borer (EAB) and native North American parasitoids. Photo by: Justin M. Gaudon

Part of my PhD research focuses on augmentative biological control of EAB, where the idea is to transport parasitoid-infested ash logs to new sites where they have the potential to increase native parasitoid populations in recently EAB-infested sites and where these native parasitoids have not yet been observed.
This approach of introducing and augmenting native natural enemies in new areas may be a cost-effective and environmentally-sound approach to combating alien invasive species, such as EAB, and provide a more sustainable approach to management than traditional insecticide applications or introductions of non-native species in classical biological control.

Preliminary results of my work suggest that native parasitoid populations can be increased one year after transporting parasitoid-infested material and that augmented parasitoid populations can add to EAB-mortality in newly-colonized sites. If these initial observations remain and EAB are suppressed, then their populations will spread more slowly and overall ash tree mortality could be reduced. This, in turn, would allow for not only continued survival and reproduction of ash trees, but also the discovery of potential natural EAB resistance in ash populations. In addition, this will provide municipalities and other landowners with more time to prepare, budget, and take action against EAB by planting new tree species and creating a more diverse urban forest with increased resilience against the next invasive species to arrive.

EAB will likely be a "pain in our ash" for quite a bit longer, but I am certain that parasitoid wasps are one piece of the puzzle that may help us eventually slow the spread of EAB and “save our ash”.

Justin Gaudon

Ph.D. student

Faculty of Forestry, University of Toronto

E-mail: justin.gaudon@mail.utoronto.ca