Stick Insect Baculum extradentatum

Physiology Friday is a monthly column by UWO PhD candidate Katie Marshall and will feature new Canadian research on insect physiology.


Nitric oxide (NO) is usually overshadowed in fame by its more famous cousin laughing gas, but it’s difficult to think of many simple molecules that have such a variety of important biological functions.  While NO only lasts a few seconds in the free gaseous state in the blood, it has been implicated in processes that involve everything from immune function to neurotransmission.  One important role for NO is in the cardiac system, where it functions as a vasodilator and in vertebrates it slows heart rate, while in insects it has the opposite effect.

Stick Insect Baculum extradentatum

Baculum extradentatum photo by Sara da Silva

Most of the research about the physiological functions of NO has focused on vertebrates, but recent work published in the journal of Cellular Signalling by graduate student Sara da Silva and her postdoctoral fellow mentor Rosa da Silva in the lab of Angela Lange (University of Toronto Mississauga), has shown that, unlike other insects, the Vietnamese stick insect Baculum extradentatum can respond to NO like a vertebrate.

“Our initial research interests in cardiac physiology were influenced by earlier work indicating that stick insect hearts are innervated and can be modulated by endogenous chemicals [like NO],” says study director and University of Toronto Biology professor Angela Lange.  “It is for this reason that we chose this understudied organism, which contains a simplified cardiovascular system that can be considered a model for work on other cardiac systems.”

The researchers first attempted to find the natural source of NO in the stick insect by removing hemolymph (blood) samples and staining for the presence of an enzyme that produces NO.  Then they examined the effects of NO on heart rate by dissecting the dorsal vessel out and maintaining it in a Petri dish with physiological saline.  They could measure heart rate through the placement of electrodes on either side of the dissected heart, and monitor the effects of various chemicals on the cardiac activity of the stick insect.   They also could examine whether heart rate was mediated by the central nervous system by leaving the nervous system attached or not.

insect heart rate

The effects of nitric oxide on the heart rate of B. extradentatum. Figure 3 from da Silva et al. 2012

They found that the hemocytes (blood cells) of the stick insect were producing an enzyme that was similar to the enzyme other animals use to produce NO.  In addition, the more of a chemical called MAHMA-NONOate (which produces NO) they added, the slower the stick insect hearts beat.  This surprising effect was completely opposite to what had been found in other insects and was more like the response of the vertebrate heart.

“Insects have evolved different strategies depending upon life history, and have co-opted different messenger systems for this success,” says study author da Silva. “We need to understand the full ecology of all species to finally appreciate the factors involved.”

Using the same setup, they also tested other components of a system of compounds that they thought might be involved in the pathway that produces NO that leads to decreased heart rate in B. extradentatum.  They believe that NO is produced in the hemocytes, travels to the wall of the heart, and then leads to the production of a messenger molecule that decreases heart rate.

Schematic diagram of the proposed regulation of cardiac activity in B. extradentatum by the gaseous signaling molecule, nitric oxide (NO)

Schematic diagram of the proposed regulation of cardiac activity in B. extradentatum by the gaseous signaling molecule, nitric oxide (NO). Figure 7 from da Silva et al. 2012.

“This study further emphasizes the evolutionary links between the physiological processes of vertebrate and invertebrate systems,” says da Silva. “Our findings suggest that signaling molecules (such as NO) common to both types of organisms can have similar effects on cardiac activity.  These novel findings demonstrate that the study of vertebrate systems can be complemented with studies in model invertebrate organisms.”

da Silva, R., da Silva, S.R. & Lange, A.B. (2012). The regulation of cardiac activity by nitric oxide (NO) in the Vietnamese stick insect, Baculum extradentatum, Cellular Signalling, 24 (6) 1350. DOI: 10.1016/j.cellsig.2012.01.010

My name is Chris Buddle – I’m an Associate Professor at McGill University, in Quebec, Canada, and the Editor-in-Chief for The Canadian Entomologist. I have worked at McGill University, in the Department of Natural Resource Sciences, for about 10 years. As a Professor, my work involves all three aspects of academia – teaching, research, and service.

For teaching, I instruct undergraduate courses in our “Environmental Biology” program – this involves teaching courses in both my own area of expertise (entomology) as well as in more general areas (e.g., ecology).

My research program is quite varied; although originally hired as a “Forest Insect Ecologist” my research expertise is broader than that, and I currently oversee graduate students working on insect pest management, the ecology of herbivorous insects in forest canopies, and the biodiversity of Arctic arthropods. The latter initiative is part of a larger-scale project titled the Northern Biodiversity Program.

For “service” I devote a lot of time and energy into my position as the Editor-in-Chief for the Entomological Society of Canada’s flagship journal The Canadian Entomologist (TCE) – a journal that joined a publishing partnership with Cambridge University Press in January of this year.

TCE is an excellent scientific journal, and I am honoured to be associated with it. Its excellence is in part because of TCE’s long history as an internationally renowned entomology journal – it has been published continuously since 1868. TCE is a journal with particularly high editorial and technical standards. We pride ourselves on serving authors well, and on producing a product that has been carefully edited, and that is technically clean. TCE is one of the relatively rare entomology journals that publishes on all facets of the discipline, including taxonomy and systematics, biodiversity and evolution, insect pest management, behaviour and ecology, and more.

We are, therefore, an entomology journal for all entomologists – anyone interested in arthropods can generally find an article of relevance within its pages. I’m also excited about TCE’s new partnership with Cambridge. This publishing house has an equally impressive history, and an equally high standard of publication quality. With this partnership, authors no longer pay page charges for TCE, and receive a complementary PDF of their articles.

As Editor-in-Chief, I have an opportunity to help guide the journal into the future. My editorial objectives include a balance of doing what we have done well in the past (i.e., high quality standards), but also seeking some new opportunities. For example we are initiating a plan to produce a topical “special issue” of TCE every year, for the first issue of each volume. For Volume 145 (the year 2013), we will be devoting an entire issue to the topic of “Perspectives on Arctic Arthropods“. This is an extremely important area of study given the current global concerns about changing climates, especially since some of the effects will be most acute in polar regions. The call for papers for this special issue went out at the end of January, and authors have until 15 June 2012 to submit their manuscripts.

Another objective I have is to continually improve our service to authors. Our move to an on-line manuscript submission system is helping this tremendously and I am continuing to work with my editorial team to tweak the system for the benefit of our authors. I am also interested in bringing entomology, and TCE, to a broader audience. Entomology is a vast and wonderful discipline, but the pages of entomology journals often target a specialized audience. I think a lot of what we publish in the journal is of broad interest, and for that reason, I tweet for the Entomological Society of Canada’s twitter account (follow us: @CanEntomologist). This is an effective way to use social media to highlight articles we publish, activities of the Entomological Society of Canada, and other interesting entomology events and stories. We also have plans to work with our society to develop a blog devoted to entomology in Canada, and TCE will be featured prominently on this blog.

I would like to conclude with a few words of advice for up-and-coming entomologists looking to publish their work. The publication ‘game’ can be a complex one, and it is a changing landscape that can be difficult to navigate. In addition to thinking about the traditional metrics when considering different journals, I do recommend that all potential authors look carefully at the “aims and scope” section for potential venues for publication – it is important that your work will be a good fit with the journal. It’s also easy to be swayed by numerous journals that are sprouting up and seem to be offering everything for nothing. Some journals may seem attractive at first glance, but be aware that quality of service, and the quality of the editorial process, may be less than what could be offered by journals backed by a publisher with strong credentials. More ‘traditional’ journals often have an incredible amount of behind-the-scenes support, and this matters. I will also stress that all authors must strive for a clean, concise, and well-written manuscript. I cannot state strongly enough that careful writing and proofreading is of paramount importance.

In sum, it’s truly a delight to be associated with The Canadian Entomologist and its publication partner, Cambridge University Press. The future is bright for the journal, and I am exciting to work hard to increase the profile and readership of TCE, all the while maintaining its history of excellence. I have assembled a strong editorial team of 20 subject editors, and have additional support from my Editorial Assistant, Dr. Andrew Smith. We are all here to help you publish your best entomological research, and get it into the hands of an international audience.

Read the first issue of the year for free here


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By Michel Cusson, ESC President

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?

This post was chosen as an Editor's Selection for ResearchBlogging.org1Bezier, 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