Nicotine-Puffing Caterpillar Uses 'Defensive Halitosis' To Ward Off Wolf Spider Predators
What do 81 percent of Americans and 100 percent of wolf spiders have in common? (This is something you could never actually guess, so don't try.) Well, like the aforementioned Americans, it turns out that wolf spiders do not like nicotine. That's one of the interesting findings of a study published today in Proceedings of the National Academy of Sciences, which discovered that hornworm caterpillars sup on plants with nicotine and then puff it out of holes in their body to repel predators.
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Researchers discovered the hornworm caterpillar's nicotine-puffing technique, called "defensive halitosis," while trying to determine how the insect was capable of eating the nicotine of tobacco plants, which is usually toxic. The researchers began by feeding both regular tobacco plants and genetically modified tobacco plants (which had the nicotine removed) to hornworm caterpillars, in order to determine what effect nicotine has on the caterpillar's genes. They found that a gene called CYP6B46 (you know the one) was activated in the guts of caterpillars after ingesting nicotine. The CYP6B46 gene pushes the nicotine into the bloodstream of the caterpillars, allowing them to release it out of their bodies to repel spiders (and to prevent toxic nicotine from killing them).
The next step was to interfere with the CYP6B46. That was accomplished by placing RNA interference in the tobacco plants, preventing the caterpillars from using their nicotine-puffing defense. The researchers placed these nicotine-deprived caterpillars alongside wolf spiders, and you can probably guess what happened: goodbye caterpillars.
"It's really a story about how an insect that eats a plant co-opts the plant for its own defense," said study researcher Ian Baldwin, a professor at the Max Planck Institute for Chemical Ecology in Germany.
As National Geographic notes, the sort of "chemical theft" practiced by hornworm caterpillars is not uncommon in animals. "For example, the eastern tent caterpillar munches on plants that are loaded with hydrogen cyanide, which it then vomits onto marauding ants," writes National Geographic's Ed Yong. "But nicotine is too deadly to store. Instead, the tobacco hornworm has evolved a way of getting rid of it, which also doubles as a potent defense."
Between the defensive halitosis of the hornworm caterpillar and the defensive regurgitation of the eastern tent caterpillar, it turns out that caterpillars defend themselves in some unusual and disgusting ways. Who knew?
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