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Caterpillars Use Nicotine to Ward off Predators

Update Date: Jan 02, 2014 03:41 PM EST

Nicotine is a toxic substance that can be found in tobacco. The colorless or sometimes, yellowish oily liquid is a stimulant when taken in small amounts. However, if consumed in large amounts, nicotine can inhibit automatic nerve and skeletal muscle cells' functions, which could lead to paralysis or death. Even though large amounts of nicotine can kill every animal, a new study found that there is one exception, the tobacco hornworm.

According to researcher Pavan Kumar and colleagues from the Max Planck Institute for Chemical Ecology located in Germany, the tobacco hornworm, which is a caterpillar, eats tobacco leaves on purpose so that it can use the nicotine to ward off predators. For their analysis, the researchers identified the process the tobacco hornworms take when they intake tobacco leaves. After ingesting the leaves, the hornworms are capable of exhaling the poison from the nicotine through the pores on their skin. The vapor that surrounds the hornworms deters hungry spiders from wanting to eat them. This defensive mechanism is called defensive halitosis.

The data the team compiled came from over two years of research. The team started raising hornworms in 2010. The hornworms were fed a genetically modified tobacco that did not contain nicotine. The caterpillars that ate this type of tobacco had a less active CYP6B46 gene in comparison to caterpillars that ate regular tobacco. The researchers believe that CYP6B46 might be involved with regulating the effects of nicotine on the caterpillars. They tested this theory by feeding the hornworms genetically modified tobacco that would deactivate CYP6B46. The researchers discovered that after a while, the hornworms that ate the altered leaves were more likely to die from being ingested by wolf spiders.

The researchers found that CYP6B46 was capable of moving some of the nicotine from the guts to the caterpillar's haemolymph, which is the insect's bloodstream. From there, the caterpillars are capable of releasing the nicotine through their pores. The researchers found that only around 0.65 percent of the nicotine the caterpillars' intake ends up in the haemolymph. Even though this is an extremely small amount, the toxic air is enough to fend off predators.

The research was published in PNAS.

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