Articles

By Dr. Laurel Haavik, US Forest Service

Exotic species that establish, spread, and cause substantial damage are demonized as foreign invaders that charge with menacing force across the landscape. Rightly so; those pests threaten to displace or eliminate native species and alter ecosystem functions. Chestnut blight, emerald ash borer, and hemlock woolly adelgid are all excellent examples. What about invaders that aren’t so destructive? Or, at least don’t seem to be at the moment? At what point do we stop monitoring a seemingly innocuous invasive species, especially one that has proved itself a serious pest elsewhere? To make this decision, it’s helpful to know how much the species has affected its new habitat, and whether this impact already has or is likely to change over time. That is exactly what we set out to do with the European woodwasp, Sirex noctilio, in Ontario.

Nearly a decade after the woodwasp was first found in a trap near the Finger Lakes in New York (and then a year later across Lake Ontario in Sandbanks Provincial Park), it still hadn’t killed pines in noticeable numbers, either in the US or Canada. Native to Europe and Asia, this woodwasp has been introduced to several countries in the Southern Hemisphere, where it has been a serious pest in forests planted with exotic pines. By contrast, in North America, it seems that only the weakest trees, those that are already stressed by something else, are killed by the woodwasp. Would forests with many weakened trees allow populations of the woodwasp to build up enough that they could then kill healthy trees in well-maintained forests? Could we find any evidence that this had already happened or would likely happen in the future?

Our goal was to measure the impact the woodwasp has had in Ontario, and whether that has changed over time, by closely examining the same trees in pine forests every year. First, we had to find sites where the woodwasp could be found, which wasn’t every pine forest, and where landowners would allow us to work. We were not interested in sites that were well-managed, because research had already confirmed that the woodwasp was not present in those forests. We used records of positive woodwasp captures from the Ontario Ministry of Natural Resources trap survey as a guide. We visited 50 potential sites, and eventually selected eight for close scrutiny in our long-term study. These sites were areas where there was likely to be intense competition among trees for resources, with plenty of stressed trees for the woodwasp.

The European woodwasp was probably absent from a well-managed red pine forest (left), but likely to be found in an un-managed scots pine forest (right).

We visited all eight sites every fall from 2012 to 2016, after woodwasps had the opportunity to attack trees. Adult woodwasps mate and lay eggs, attacking trees in the process, in mid-summer. Attack was visible as distinctive resin beads scattered over the trunk. We recorded which trees had been attacked, and later (usually the following year) killed by the woodwasp.

The woodwasp population was considerable at some of our sites, having killed about one-third of the trees within five years. Though at other sites, the population was much smaller, having killed only a small percentage of trees. We’re not exactly sure what caused this variability. It’s possible that the woodwasp arrived at some of our sites years before it arrived at others, and the most vulnerable trees were long dead at the sites it invaded earlier. We have no record of time since woodwasp invasion at any of our sites. It’s also possible that local environmental conditions, which we did not measure, could in some way have affected tree resistance or the woodwasp population.

Most curious, though, was that over the five years many trees attacked by the woodwasp did not die – around 50 to 80%. At least half of these trees were attacked again and again in successive years. We had captured an interesting part of the woodwasp’s ecology, its way of essentially priming trees to become better habitat for its young. When laying eggs, female woodwasps also inject a self-made toxic venom along with a symbiotic fungus into the tree, to help kill it. If the tree is sufficiently resistant to attack, the female may not lay eggs, only the fungus and venom. The fungus and venom then work in concert to weaken (prime) the tree for re-attack – and hopefully successful colonization – in subsequent years.

Female woodwasps sometimes die while laying eggs. Survival of the fittest?

Two-thirds of trees that were attacked by the woodwasp at some point in our study (one or more times) did not die, which shows that most trees selected by the woodwasp as suitable habitat are at the moment resistant to its advances. This also shows, along with the variability in woodwasp impact among sites, that this invader is active in the forest. Should environmental conditions change (say, if a drought occurs), woodwasp populations could quickly rise to outbreak levels, which could kill large numbers of healthy pines. This has happened in other places.

Long-term study of these sites, and hopefully others, is needed so that we can be aware of changes that arise in woodwasp impact. This will allow us to be proactive about what steps to take to manage this invader, should it become a problem. It will also help us better understand and predict what causes exotic species to vacillate on the spectrum between aggressive invader and innocuous resident.

Want to read more? Check out the original article published in The Canadian Entomologist, which is freely available for reading & download until May 14, 2018.

Haavik, L.J., Dodds, K.J. & Allison, J.D. (2018) Sirex noctilio (Hymenoptera: Siricidae) in Ontario (Canada) pine forests: observations over five years. The Canadian Entomologist, 1–14. doi: 10.4039/tce.2018.18

Cerceris 560

New « field assistant », getting its unique identifying paint job.

I’m pleased to announce the following Canadian Entomologist paper as this issue’s Editor’s Pick: The use of Cerceris fumipennis (Hymenoptera: Crabronidae) for surveying and monitoring emerald ash borer (Coleoptera: Buprestidae) infestations in eastern North America.

It was written by Philip Careless, Steve Marshall and Bruce Gill.

This link will be active and freely available for the next month, so do not worry about a paywall.

This research focuses on using natural history information to assess creative ways to monitor one of eastern North America’s most important invasive, exotic tree-feeding pests, the emerald ash borer (EAB).  The Crabronidae species Cerceris fumipennis is a wasp that is known to provision its nests with metallic wood-boring beetles in the family Buprestidae. Therefore, there is potentially to find out where EAB is located based on whether nests of the wasps contain that particular beetle. It’s a clever approach, and although the basic biology of the system was already known, Philip and colleagues worked to quantify and fully assess this potential biosurveillance tool for the EAB. We need to know where this pest is, and an indicator such as C. fumipennis holds much potential.

I caught up with Philip and he kindly answered a few questions about this work:

What inspired this work?

Almost all graduate work begins as a spark in the advisor’s mind.  Certainly this project came from the creative thinking of Dr. Stephen Marshall so he deserves credit for that.  I was simply fortunate enough to be the one chosen to run with the idea.  Though, more importantly, he and the rest of the advisory committee gave me enormous freedom to transform the question into a journey through the strange world of solitary wasps.  As for fueling the fire, I would say it was the writing of entomologists like Howard Evans, a healthy dose of nature documentaries, and correspondence with enthusiastic forest managers like Troy Kimoto who are struggling to address pressing conservation challenges.

What do you hope will be the lasting impact of this paper?

I hope that it will help people think of other novel ways to utilize the often overlooked services that insects all around them provide and in turn care for and conserve biodiversity.  In our case an insect that the public instinctively hates, fears, and kills has been transformed into an amazing, useful, and valued colleague.

Where will your next line of research on this topic take you?

We have over 370 nest-provisioning solitary wasps in Canada. Each species is eloquently designed to collect their specific preferred taxa – eg. Stictiella takes adult Lepidoptera, Isodontia takes Orthoptera, Crossocerus takes Psocoptera, etc.  The next steps will be to look at our native wasps, identify what they provision with and then determine if they are well-suited to life as a biosurveillance tool – assisting with life science inventories or monitoring pests.  As the prey choice of most solitary wasps is unknown, professionals and amateurs alike can assist by photographing provisioning wasps and uploading the images to bugguide.net or the like.

Do you have any interesting anecdotes about this research?

Sitting in the middle of a ball diamond under a beach umbrella with a butterfly net (watching wasps provision their nests) tends to draw a lot of curious looks and questions from passers by.  On one such occasion in Windsor, Ontario – while showing a dog walker my prized wasp bringing back a beetle – I observed a novel form of predation.  As the prey-laden female wasp diligently droned past us to the nest, the dog – previous quite bored – snapped it out of the air and ate it, prey and all!  We humans were both surprised but the dog seemed quite pleased.

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Brenna Wells hard at work, waiting to steal beetles from wasps.

For more information on this initiative, or even to get involved yourself, please visit the project website.

Dr. Christopher Buddle

Editor, the Canadian Entomologist

@CMBuddle

By Justin Renkema, Post-Doc, University of Guelph

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It was an early morning after a long drive from Guelph to a small fruit farm in Chatham-Kent where my undergraduate student, Caitlyn, and I were conducting a small-plot spray trial to test the effect s of repellents against Drosophila suzukii (Spotted Wing Drosophila), a recent invasive and serious fruit pest.  I knew the raspberry patch was heavily infested with D. suzukii so before getting to work, to amuse ourselves at the start of the day, I started gently shaking canes, and we watched the swarms of fruit flies disperse and hover over the fresh fruit.  However, as I went to grab a branch low to the ground, I noticed something different about one of the fruit flies sitting on a leaf.  It had characteristic white “racing stripes” along its thorax, unlike any other fruit fly I had seen.  This was it!  This was very likely Zaprionus indianus or African fig fly, another invasive and potential fruit pest that we knew was moving northwards from the southeastern USA.  Caitlyn grabbed a vial and we successfully had, on 10 September 2013, what we thought was the first capture of this fly in Ontario and Canada.

Zaprionis indianus photographed by Dr. Stephen Marshall in Africa. (Photo C Stephen A. Marshall, used with permission)

Zaprionis indianus photographed by Dr. Stephen Marshall in Africa. (Photo © Stephen A. Marshall, used with permission)

 Indeed the fly was Z. indianus, as determined by Meredith Miller, a M.Sc. student at the University of Guelph working on taxonomy of Drosophila spp. in Ontario.  Through contact with Hannah Fraser at Ontario Ministry of Agriculture Food and Rural Affairs, we learned that their Ontario-wide monitoring program for D. suzukii had also picked up some African fig flies in apple-cider vinegar traps, and a few at an earlier date than our find in Chatham-Kent.  Colleagues in Quebec (Jean-Phillipe Légaré and others at MAPAQ) had also found what they believed were Z. indianus.  Once all the material was collected and examined by Meredith, we submitted a scientific note documenting our Z. indianus discovery in Canada that was published by the Journal of the Entomological Society of Ontario.

Zaprionus indianus is native to the Afrotropical region.  It was found in Brazil in 1998 where it was given its common name because it became a significant pest of figs.  In 2005, Z. indianus was discovered in Florida and has since been found successively further north and west in the USA (see a map of its distribution here).  It is likely that the North American infestation did not come from the Brazilian population.  Zaprionus indianus is the only member of Zaprionus present in Canada, and therefore the reddish-brown head and thorax and particularly the silvery stripes that extend from the antennae to the tip of scutellum can be used as distinguishing features.

Zaprionis indianus dorsum showing characteristic white stripes

Unlike D. suzukii (thankfully!), female Z. indianus do not possess heavily sclerotized and serrated ovipositors and are not currently seen as a serious threat to temperate fruit crops.  They have been reared from a number of tropical, tree-ripened fruits in Florida and there is concern in vineyards in the eastern USA, where sometimes they outnumber D. suzukii in traps. It is possible that Z. indianus can use fruit that has been oviposited in by D. suzukii, thus increasing damage and possibly complicating control measures.  In Canada, particularly Ontario and Quebec, winter temperatures may preclude establishment of African fig fly, and yearly re-infestation from the south would be necessary for it to show up in future years.  At all but one site, we found just 1-4 flies during late summer and early fall per site, so it will be interesting to see what happens to numbers this coming growing season.  In tropical and sub-tropical locations much larger populations have been detected the year following first detection.

For the past 1.5 years I have been working as a post-doctoral fellow at the University of Guelph with Rebecca Hallett on D. suzukii.  We are developing a push-pull management strategy using volatile plant compounds to repel and attract this pest.  With the occurrence of Z. indianus and possible reoccurrence  in larger numbers in the future, we may have a unique opportunity to study how two recent invaders using similar resources interact, and also, perhaps, a more significant challenge ahead of us  in developing management strategies.  If you are interested in this topic or have current or future experiences with Z. indianus, I and co-authors on the scientific note would appreciate hearing from you.  You can contact me at renkemaj@uoguelph.ca.

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Renkema J.M., Miller M., Fraser H., Légaré J.P. & Hallett R.H. (2013). First records of Zaprionus indianus Gupta (Diptera: Drosophilidae) from commercial fruit fields in Ontario and Quebec, Canada, Journal of the Entomological Society of Ontario, 144 125-130. OPEN ACCESS [PDF]

pentatomidae 1

This season is full of green and red decorations, and exhortations about family, so I thought I would share this lovely family portrait of some 1st instar stink bugs exemplifying the togetherness of the holiday season. I found this family group in Fort Pierce, Florida on the underside of a Brazilian Peppertree leaf. Schinus terebinthefolius is an invasive plant brought in as an ornamental for its beautiful red berries and evergreen leaves (and used in Christmas decorations!). Not surprisingly, entomologists are on the lookout for a insect-based solution for peppertree control!

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