Brown bark-colored moth with orange stripes on body

Today I just happened to see a Carolina sphinx moth outside the East Lansing, Wild Birds Unlimited store. Many gardeners might be upset to see the green Tobacco Hornworm (Manduca sexta) devouring their potato, tomato or eggplant leaves but this green caterpillar eventually completes a metamorphosis into a large fascinating bark-looking moth with an orange striped abdomen.

These moths are important pollinators of deep-throated, night-blooming flowers. While they extend their long proboscis into different flowers to collect nectar, pollen grains stick to them and the plants become pollinated.

While I was looking up this information, I just happened to discover a press release about a recent study out of Duke University:

A new explanation for how caterpillars know when to start the transformation into moths or butterflies.

Caterpillars molt four to five times before morphing into an adult as a moth or butterfly. Duke University biologist Fred Nijhout knew from earlier work that Tobacco Hornworm caterpillars, only start a molt when they reach a critical weight.

In the new study, Nijhout and his graduate student, Viviane Callier, measured the size of the caterpillar's respiratory system. They found that the insect's tracheal tubing is fixed in size at each stage of its larval life. Other parts of the caterpillar's body can grow, but not the respiratory tubing. As a result, the insect eventually begins to suffocate. The only way it can continue to mature is to shed the old tubing for newer, longer ones.

This is the first time scientists have figured out a factor -- in this case, lack of oxygen -- that regulates an animal's body size during specific developmental stages, said Nijhout, who led the study. The research appears online in the Proceedings of the National Academy of Sciences.

Body size is a fundamental trait for all organisms and affects everything from how they move to the mates they choose. In humans, size, measured as height, is also associated with risks for disease.

In the new study, Nijhout tested oxygen's effects on the caterpillars' body size by placing the larvae into airtight glove boxes and pumping in air with different amounts of oxygen. Under hypoxic conditions, the caterpillars molted at body sizes well below the critical weight. And, despite the caterpillars doubling in body size during the growth phase, they did not increase the size of the tracheal tubes, according to the results.

Harrison said that together, these observations suggest that insects molt to the next juvenile or adult stage partly to ensure that their oxygen delivery capacity can match the oxygen needs of the tissue.

Because the research is specific to caterpillars, it cannot explain why humans grow to a specific size. But, Nijhout said, caterpillars' abdomen-based, low-oxygen sensor may be related to the system that produces insulin-like growth hormones in humans, and studying it further could provide information about a broader biological process that affects how diverse organisms travel their paths to adulthood.

Sources:

-Press Release from http://today.duke.edu/2011/08/suffocating-moths

-Species Detail: Carolina Sphinx (Butterflies and Moths of North America) http://www.butterfliesandmoths.org/species/Manduca-sexta

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