Nouvelles
This wasp has a problem! Three relatively enormous parasitic strepsipterans are occupying her abdomen…Photo by Sean McCann.
Who wouldn’t want to get to know the Strepsiptera? These animals are extremely odd, being obligate endoparasites of other insects, with a free-flying male and an eyeless, wingless female that never leaves the abdomen of her host. Different families of these parasites infect different hosts, ranging from silverfish and cockroaches to solitary and social wasps, leafhoppers, and froghoppers.
Allow me to introduce Xenos peckii, a strepsipteran parasite of Polistes fuscatus, the Northern Paper Wasp. As an entomologist, I have long been interested in these little-studied insects, so I was thrilled to get to help my colleague Mike Hrabar in his investigation their life history and reproduction.
Mike collected a several colonies of infected wasps from Maine and brought them back to the lab to observe their emergence, flight and mating behaviour in a systematic way. We used high speed videography and careful record keeping to document their life history in closer detail than had ever previously been recorded.
Not really bling. This wasp sports a heavy infestation of four developing Xenos, costing vast amounts of resources. Photo by Sean McCann.
From my perspective, one of the coolest things we learned is that the free-flying male opens his puparium by means of blade-like mandibles, which are used to cut along a zone of weakness in the pupal cap, functioning like a tiny can opener!
Head of male Xenos peckii. Note the scissor-like mandibles and the large and unusual compound eyes. Photo by Mike Hrabar. Figure 3G from Hrabar et al. 2014.
Check out the video below to see the male’s little mandibles working the cap open.
[youtube http://www.youtube.com/watch?v=aCeEsXVNiOY?rel=0&w=560&h=315]
These little troopers fly immediately upon emergence, in stark contrast with most other insects, which need time to inflate and harden their wings. In fact, once the males begin beating their wings, they remain in flight continuously except for a brief period during mating.
Before our study, biologists had assumed that female Strepsiptera were completely immobile and passively waited for males to find them, but we observed that they move to adopt a distinct calling posture, elevating their cephalothorax up from the wasp’s abdomen, likely emitting a pheromone plume.
Female Xenos peckii in the abdomen of a Polistes fuscatus. This female is in the calling posture, elevating her cephalothorax. Photo by Mike Hrabar. Figure 4D from Hrabar et al. 2014.
The males smell this pheromone plume and fly toward it rapidly, in a zig-zag fashion reminiscent of pheromone-questing moths. As soon as a male reaches the female-infected host, he lands on her abdomen and walks down to where the female protrudes, using backwards steps with his heavily-modified tarsi.
Mid leg of Xenos peckii male. The tarsi are highly modified for gaining a strong grip on a wasp abdomen while searching for and mating with a female. Figure 8 from Hrabar et al. 2014.
Mating occurs rapidly, with typical copulation time being 3-5 seconds. As soon as mating is finished, the male is once again in flight, presumably in search of another female. After copulation, the female immediately withdraws from the calling posture and ceases calling other males. The following video was taken at 1000 frames/second with a high-speed video camera and shows the sequence from just after landing by the male through the majority of copulation.
[youtube http://www.youtube.com/watch?v=QPiG8AV0XWY?rel=0&w=560&h=420]
This male Polistes fuscatus was weakening, and died while we were watching. Mike pinned the host, and we forgot about it for a while, until glancing at it we realized that one of the males was emerging! This shot was snatched quickly while the male had just popped off his cephalotheca. Photo by Sean McCann, Figure 2E from Hrabar et al. 2014.
We have shown that female Xenos are not just a passive receptacle or bag of eggs, but rather play a physically active role in soliciting mates. The male emergence is facilitated by using sharp mandibles to cut around an ecdysial suture line, and navigating the surface of his prospective mates host is aided by his extremely modified tarsi.
The short-lived males face a great challenge to locate and fly to a host with a calling female in the short amount of time they live (on average 2-2.5 hours). They are in constant flight from emergence until death with only a very short pause for mating. The female, by contrast, remains alive in her host, maturing a brood of eggs which she retains in her body until they hatch and crawl from her brood canal as motile planidial larvae.
These larvae will exit the brood canal at some point, but it is unclear exactly where they manage to find new hosts. It is possible they « deplane » at flowers and wait for a ride on a Polistes to a new nest of victims. Much more research will need to happen to fully understand these fascinating insects, but we have made a start at uncovering some of the mysteries of their emergence, communication and reproduction. Many more questions remain unanswered and provide opportunities for any natural historian to explore.
If you would like to read the whole paper, you can find it on the Canadian Entomologist site here, or if you are not a subscriber, I am hosting a corrected proof here.
The full citation for this paper is:
HRABAR, M., DANCI, A., MCCANN, S., SCHAEFER, P. W., and GRIES, G. 2014. New findings on life history traits of Xenos peckii (Strepsiptera: Xenidae). The Canadian Entomologist doi: http://dx.doi.org/10.4039/tce.2013.85 pp.1–14.
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.
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 © 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.
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]
Catherine Scott and I continue on our Honduran odyssey, finally making it out into the field to begin our work on Red-throated Caracaras. We are working in a medium-elevation pine forest, consisting of mainly Pinus oocarpa and a couple oak species. This makes the surroundings seem very much like the foothills of the Rockies, except the species composition is way off!
In these pine forests, one of the main defoliating species are fungus-rearing leafcutter ants!
On some of the flowering plants, mantids lie in wait of unwary pollinators.
Catherine Scott and Isidro Zuniga, our main Honduran collaborator, check out the cryptic mantid.
Being weird gringos, and something of a novelty, we get great opportunities to chat with curious kids. Some of them are really enthusiastic about birds and insects, and some can be persuaded to show us where to find the cool bugs.
We will keep searching out these cool bugs, as our Honduras fieldwork continues. Please stay tuned for more updates from the field, when and where we can fit them in.
While out visiting our friend Rafael’s ranchito yesterday, we were surrounded by a herd of curious cattle. These were a mix of both Brahmas and Holsteins, with some crosses as well. One animal in particular caught my eye; it appeared to have bot emergence holes on its sides.
I asked Rafael what these were, and sure enough, he told me that these were « torsalo », basically the same New World bot that scientists are always getting in the Neotropics. I was not aware that Dermatobia hominis parasitizes cattle, but apparently it quite commonly does so. It makes sense, as emergence sites of Cattle Grubs would be higher up on the back of the animal.
I love it how my entomological training really gets awakened when travelling in new areas.
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