wasps – Entomological Society of Canada

By Matthias Buck, Royal Alberta Museum, Edmonton

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For many of us who are working as taxonomists, describing new species has become somewhat of a routine. Sometimes it can even become a burdensome chore: I am thinking about those of us who work on hyperdiverse groups of insects in the tropics where almost every species is undescribed (case in point: one of my former lab mates recently described 170 new species of a single genus of Diptera in one paper!). However, the feeling is very different when new species unexpectedly show up in iconic groups that were thought to be well-known. Suddenly, common and familiar creatures turn into an exciting new research frontier, providing a fresh rush of adrenaline!

Mug shot of a female of Polistes hirsuticornis Buck. Vespidae Wasp

Mug shot of a female of Polistes hirsuticornis Buck. The hairs on the basal articles of the flagellum are longer than in related species (Photo credit D.K.B. Cheung & M. Buck).

This is what happened a few years ago when I started working on the vespids of the northeast. The family Vespidae (which includes mason wasps, paper wasps, yellowjackets and hornets) is most diverse in warmer parts of the World, as is the majority of stinging wasps. Doing a review of the northeastern Nearctic fauna therefore didn’t seem to be a very promising project for taxonomic novelty. Especially considering that the fauna of the eastern half of the continent is significantly less diverse and far better known than that of the west.

To my utmost surprise the study (published 2008 in the Canadian Journal of Arthropod Identification) not only turned up four new species of mason wasps but also two new paper wasps (Polistes). As you know, paper wasps are some of the most iconic species in the world of wasps, almost as much as their odious relatives, the yellowjackets. Further to that, they have received great attention as model organisms for the study of social behaviour and its evolution in insects. Finding not only one, but two new species in a group like this was beyond what I expected in my wildest dreams.

So how did it come to pass? As a novice to paper wasps I expected that reviewing the taxonomy of such a high-profile group would be like a walk in the park. Weren’t there scores of scientists before me who seemingly had no difficulties in identifying these sizeable and handsome insects for their behavioral studies, filling up cabinets of specimens in collections across the continent? Or so I thought! After months of fruitless staring through the microscope my nonchalant attitude gradually turned into frustration. One of the species, the common and widespread Northern Paper Wasp (Polistes fuscatus), was so variable that it blended virtually into almost every other species in the same subgenus. Previously published keys gave me a pretty clear sense of what typical specimens of each species look like, but where were the objective criteria that would allow me to identify the numerous intermediate forms? Truly, I found myself in a taxonomic quagmire!

Aedeagus (penis) of Polistes parametricus Buck. The size, shape and position of teeth is diagnostic with regard to P. fuscatus and P. metricus, with which this species was previously confused (Photo credit D.K.B. Cheung & M. Buck).

Grasping for straws I turned to three taxonomic methods that had not been applied to Polistes before: DNA barcoding, detailed study of male genitalic features and morphometric analysis. During the previous months, I had rounded up a number of puzzling specimens which represented the spearhead of my taxonomic headaches, and submitted them for sequencing. The results came back like a thunderclap, turning my anguish into cautious excitement: the DNA barcodes of these troublemakerswere clearly different from any of the described species. With renewed energy I launched into a detailed morphological study which led to the discovery of several new diagnostic characters, confirming the distinctness of these wasps beyond a doubt. A lot of hard work had finally paid off, and I was looking at the first newly discovered species of paper wasps in eastern North America since 1836 when Amédée Louis Michel Lepeletier de Saint-Fargeau described Polistes rubiginosus!

Female of Polistes parametricus Buck Vespidae Wasp

Female of Polistes parametricus Buck nectaring on goldenrod in West Virginia (Photo credit: Donna Race).

Since molecular methods, and in particular DNA barcoding, have received a lot of attention in recent years, it seems opportune to share some of my experiences working on Polistes. Unlike a few other taxa (such as spider wasps, Pompilidae), vespids sequence nicely and easily from pinned specimens, which makes them an ideal group for this kind of study. I found the sequence data extremely helpful but they certainly did not provide the cure of all taxonomic confusion. Barcoding uncovered an unexpected genetic diversity below the species level, which proved to be hard to interpret in the absence of other data. In Polistes there is no hint of a “barcoding gap”, which postulates that genetic distances between individuals of the same species are (nearly) always greater than those between conspecific individuals. In fact, some of the species were genetically so similar that they differed by a mere 2 base pairs (out of 658). Nonetheless, the combination of molecular data with fine-scale morphology resulted in a quantum leap forward for Polistes taxonomy. Just days ago, I found out that a group of researchers in Germany and Switzerland are making similar progress on European paper wasps using a nearly identical approach.

My research paper on eastern Nearctic Polistes, including formal descriptions of Polistes hirsuticornis Buck and P. parametricus Buck, was published in the journal Zootaxa on October 1^st.
Matthias Buck, Tyler P. Cobb, Julie K. Stahlhut, & Robert H. Hanner (2012). Unravelling cryptic species diversity in eastern Nearctic paper wasps, Polistes (Fuscopolistes), using male genitalia, morphometrics and DNA barcoding, with descriptions of two new species (Hymenoptera: Vespidae) Zootaxa, 3502, 1-48 Other: urn:lsid:zoobank.org:pub:6126D769-A131-49DD-B07F-0386E62FF5B9

By Michel Cusson, ESC President
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For my first blog post, you’d probably expect me to talk about some hot issue pertaining to the ESC. However, I chose otherwise (at least this time) and I’ll save Society-related topics for my “Up Front” column, which you can read in the online version of the Bulletin. Instead, I’d like to introduce you to what I consider the coolest product of insect evolution: the use of symbiotic viruses by parasitic wasps to manipulate the physiology of their caterpillar hosts.

Aleiodes indiscretus wasp parasitizing a gypsy moth caterpillar. Photo by Scott Bauer.

In an unusual twist of evolutionary history, some ichneumonid and braconid parasitoids have “captured” a conventional virus and “domesticated” it so that it can be used to their own advantage in the course of parasitism. The viruses in question, known as polydnaviruses (from poly-DNA-virus, but typically pronounced “polyd-na-virus”), replicate in wasp ovaries where they accumulate in the fluid bathing the eggs, before being injected into the caterpillar during parasitization (egg laying). While the carrier wasp is completely asymptomatic, the infected caterpillar displays AIDS-like symptoms, whereby its ability to mount an immune response against the wasp egg or larva is depressed by the virus. In addition, the virus will often block host metamorphosis, particularly when parasitization takes place late in caterpillar development; this will allow the wasp larva to complete its own development before the host undergoes the traumatic events associated with the larva-to-adult transformation.

But what makes these viruses pathogenic in the caterpillar while being apparently harmless in the wasp, and how could such unusual creatures have evolved? To begin understanding the answers to these questions one first needs to know that polydnavirus genomes are permanently integrated into the chromosomal DNA of the carrier wasps. This means that all individuals within a species known to carry one of these viruses contain the viral DNA within their own genome. Production of the viral particles, however, is confined to females and occurs only in ovaries. There, copies of the integrated form of the viral genome are synthesized and packaged into a proteinacious coat known as the “capsid”. These viral particles are released into the lumen of the oviduct, where they accumulate until injection into the caterpillar host.

What’s going on “behind the scenes”. Image by Michel Cusson and Marlene Laforge.

Once injected, the virus gains access to various host tissues where some of its genes are expressed, leading to the synthesis of viral proteins that do the dirty work, i.e., depress the host immune response and perturb host development. Few, if any, of these virulence genes are expressed in the wasp, which probably explains why the wasp is asymptomatic. While the virus does not replicate in the caterpillar, it is the expression of viral genes that makes it possible for the wasp egg and larva to survive within the host. And successful development of the immature wasp is what ensures transmission of the integrated form of the virus to the next wasp generation.

Whether polydnaviruses are “real” viruses has been a matter of debate for many years. For example, some have argued that, although they look like viruses, they are nothing more than a smart device that the wasps have evolved to transfer host-regulating factors to caterpillars during oviposition. However, it is becoming increasingly clear that polydnaviruses arose from ‘conventional’ viruses.

Recently, a group from France has shown that the proteins that make up the coat of braconid polydnavirus particles are highly similar to those of ‘nudiviruses’¹, a group of conventional insect viruses that are capable of integrating their genomes into those of their hosts. So, it appears that the genome of a nudivirus became permanently integrated into the chromosomal DNA of an ancestral braconid, some 100 MYA. Since then, evolution has led to the replacement of the original nudiviral virulence genes by other genes that are usefull to the wasp during parasitism. The wasps may therefore be viewed as having ‘domesticated’ the nudivirus, turning it into a mutualistic virus – a phenomenon fairly unique in the world of viruses. Cool stuff, isn’t it?

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¹Bezier, A., Annaheim, M., Herbiniere, J., Wetterwald, C., Gyapay, G., Bernard-Samain, S., Wincker, P., Roditi, I., Heller, M., Belghazi, M. & (2009). Polydnaviruses of Braconid Wasps Derive from an Ancestral Nudivirus, Science, 323 (5916) 930. DOI: 10.1126/science.1166788

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Taxonomic adventures in the world of paper wasps (Polistes, Vespidae)

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