Beetle Breathing is Highly Complex

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An X-ray of a yellow mealworm beetle showing the system of white tubes, or tracheae, running through its body.

When I worked with and dissected insects as a graduate student, I always found their breathing apparatus to be fascinating and beautiful, although mysterious because I could only guess how their tracheae functioned while they were alive. Even though insects have a small body size, they need more than a simple, small respiratory system to provide enough oxygen to sustain their lives. Using X-rays to visualize what lies beneath their hard outer chitin layer, researchers have recently found that the bugs have a more complex breathing apparatus than previously suspected.

Confirming what I had always suspected, based on my own careful observations of the tobacco hornworm moth, Manduca sexta, a recent study in ground beetles reveals that air doesn't simply flow passively in and out of the spiracles, instead, insects actually inflate and deflate their tracheal tubes to help move life-giving oxygen through their bodies. Spiracles are tiny openings that run along the sides of insect bodies. They are connected to the tracheae, which are branching tubules inside their bodies, where oxygen and carbon dioxide exchange occur. Beetles breathe through up to 18 of these tiny spiracles that dot the middle and hind part of their bodies.

"These tubes are being compressed in rhythmic fashion, and in this species it happens in the course of a second," said researcher Jake Socha of Argonne National Laboratory in Illinois. Socha presented his team's research at a meeting of the American Physiological Society (APS) in Washington, D.C. last month.

"There's a fundamental problem with the gas-exchange system design, and this is an issue of scale," Socha noted.

Basically, as an animal's body gets bigger, its volume increases even faster than does its surface area, and the same is true for its cells. Because gas molecules diffuse into cells through their surface, the size of the surface directly affects how much oxygen can move in and out of each cell. But this random movement of oxygen molecules can only carry the incoming air so far and then it's up to mechanical processes to pick up the slack.

"If you look at a single cell, as the cell gets larger diffusion isn't going to work to get oxygen into the cell because diffusion only goes a certain distance," said Scott Kirkton of Union College in New York. Kirkton studies insect respiration but was not involved in this beetle study.

Recent studies have shown that insects, including beetles, dragonflies and cockroaches, rely on active body movements to ensure most effective respiration. Some pump their wings to move air in and out of their bodies while others squeeze their bellies to pull in the needed oxygen. These various mechanisms are all a form of convection, or bulk movement of air.

Using high-powered X-ray beams, Socha and his colleagues observed living, breathing beetles. They collected live ground beetles from a local forest and taped each to a tiny mount. They then placed the live beetles into a circular particle accelerator called the Advanced Photon Source at Argonne National Laboratory. The accelerator speeds up electrons to near the speed of light, thereby generating X-rays that are a billion times more powerful than the sort used in hospitals. Using this technology, the scientists taped a video showing the outlines of the hair-thin tracheae. They could actually see the tiny tubes squeeze and relax in a pattern of undulations that worked in a perfectly timed cycle.

"So in a second you have deflation and then rapid re-inflation. It appears to be happening everywhere at once," Socha said.

However, the scientists don't know exactly how these compressions are helping the beetle.

"The squeeze out may speed up the flow of fresh air in, aiding oxygen exchange," Socha speculated. Another idea is that by moving carbon dioxide out quicker, the spiracles would open for only a short time, which would decrease water loss from the pores. "Or it may simply move air within the body," Socha added.

Source:

MSNBC (quotes, image).

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As an undergraduate in the 60s, I learned that someone had proven insects cannot be relying on diffusion alone for respiration, but no one knew how to approach the mystery. Well, 40 years later, the technology has finally caught up. We knew there'd be pumping going on, but only now are we going to find out the specifics.

Good deal.

non grantum anus rodentum

By rev jerry (not verified) on 20 May 2007 #permalink

non grantum anus rodentum

By rev jerry (not verified) on 20 May 2007 #permalink

I am happy that people like rev jerry have no say in what actually gets studied by science. It would be sad to think of all the things we might not have or be able to do if people like him got to decide what was worth knowing.

Seeing as insects are an incredibly important part of sustaining life on earth, I think it might be in our best interests to understand them. Thats not even including the engineering ideas that could come from such understanding.

What a fool.

I always found their breathing apparatus to be fascinating and beautiful,

Comparing mammals with animals like birds and insects, our lungs seems mundane mechanisms in comparison.

Btw, to nitpick on science not central to the post, it is acceleration of charges that emits radiation, as in a radio antenna. In this case the acceleration provided by the magnets that keeps the electrons in their circular track. The relativistic speeds is what bumps the emitted radiation up to X-ray energies.

And the "power" comes from either or both of higher energy and higher brightness of the source. I would also guess that tunability of energy, dose and probably exposure time would improve the image quality.

By Torbjörn Lars… (not verified) on 21 May 2007 #permalink

Hmm. There's a little too much non expert hand waving here about the novel technique involving the X-rays. Absolute numbers and units would make it much more informative.

According to a Cornell.edu page I found, the useful X-ray output of a hospital machine is just under a Watt, so if that 109 is referring to Power and not Frequency, it makes me wonder about crispy critters. Of course, if the duration is down in the picoSeconds, then sure.

Would anyone happen to know the typical duration of dental and medical exposures? I googled for it without success.

By JohnnieCanuck (not verified) on 21 May 2007 #permalink

How long do the bugs survive this level of X-ray exposure?

Robert: Don't Feed The Trolls, and non illegitimus carborundum". ;-)

By David Harmon (not verified) on 22 May 2007 #permalink

Sorry, its just a personal thing that bugs me to the extreme when people try to say that this or that scientific endeavor has no merits.

I will refrain.

JohnnieCanuck #7
Re medical X-ray duration: "typical" is hard to define. A picture of a finger lasts about 10 milliseconds with an exposure of 5 millirads; a lateral sternum may be 400 ms with an exposure of 700 mrads. It all depends on what you want to see- soft tissue vs. broken bones, etc. I believe a dental x-ray is roughly 39 mrads- about the same as a chest x-ray or a week at the beach.

As for crispy critters, I have no idea what it would take to flambe a bug but it would have to be a LOT more than you'd ever get with a diagnostic X-ray.

By Robert G. (not verified) on 22 May 2007 #permalink