The tobacco hornworm is a caterpillar that spends its larval stage eating tobacco plants. It's amazing that the caterpillars are even able to each such a toxic plant - and now a new study suggests that the tobacco plant prevents a very unique benefit: it creates a very important defense mechanism. The results of the research, from a team at the Max Planck Institute in Germany, has revealed that the caterpillars release bad-smelling nicotine to ward off wolf spiders and other predators. The study was published in Proceedings of the National Academy of Sciences.
Nicotine is a powerful stimulant, most well known as being a chief ingredient in cigarettes. A cigarette-sized dose of nicotine is relatively safe (this does not, of course, mean that smoking is a safe pastime) but it can be incredibly toxic in large doses for humans as well as other animals and insects.
The researchers began their investigation seeking to determine how the hornworm was even able to eat tobacco. By all accounts, the nicotine levels in the plants should be too high for an insect that size. Hornworms must have evolved some kind of metabolic process that negates the toxicity, though the scientists did not know exactly how.
The study began with planting genetically modified, low nicotine tobacco in the area where the hornworms live. What the researchers observed was quite shocking: the caterpillars had lost their defenses against wolf spiders, one of their main predators. Researchers began to investigate the hornworms use of CYP6B46, a protein that has been known to neutralize toxic plants in other insects and animals.
The researchers found, however, that hornworms utilized the protein in a very unique way that affected the wolf spiders as well as the hornworms. Rather than simply circumvent the toxic effects, the caterpillars are able to utilize some of the nicotine by shifting it into the bloodstream and then venting it out from the skin. The result is a pesticide-like fog, warning wolf spiders and other predators that it contains high amounts of toxic nicotine, and therefore would not make a good snack. However, this doesn’t mean that the hornworm is safe from all predators, as there are many things that can still consume the caterpillar without becoming sick from the nicotine.