Tobacco Breath Saves Hornworm Caterpillars From Predators

PHOTO: The tobacco hornworm attacking a coyote tobacco plant in the Great Basin Desert, Utah.
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Your morning breath has nothing on the tobacco hornworm. Researchers at the Max Planck Institute of Chemical Ecology in Germany have found a gene that allows the caterpillar to take the nicotine in its diet and puff it into predators' faces to keep them at bay.

The research is published in today's issue of Proceedings of the National Academy of Sciences.

Ian Baldwin, the director of the institute, said the hornworm has a nicotine tolerance that blows all other animals, including humans, out of the water. "It's about 750 times greater than that of humans, even someone who smokes four packs a day," he told ABC News. "We found a gene that was regulated with nicotine ingestion, and we were trying to figure out what it actually does."

Even though the hornworm has a high tolerance for nicotine, it would prefer to eat something else. "The process of detoxifying nicotine is costly, so it slows caterpillars down and makes them lethargic," said Baldwin. The reason why they chomp down on tobacco leaves is to better protect themselves, thanks to the gene CYP6B46.

That particular gene allows the hornworm to take some of the nicotine it ingests and send it to its hemolymph, the insect equivalent of blood. The hemolymph is expelled through the hornworm's spiracles, small holes along the hornworms' side. If a wolf spider, one of the hornworm's natural predators, detects nicotine in the hemolymph, it backs off. "It's like toxic halitosis," said Baldwin.

Baldwin and his colleagues fed the caterpillars both a normal strain of coyote tobacco plant grown from seeds in Utah, and a specialty tobacco plant that contained genetic material to silence the caterpillars' CYP6B46 gene. The spiders hesitated to eat the animals that were fed on the normal tobacco, but readily gobbled up those that were fed the genetically altered plant thanks to the gene silencing effect.

This type of effect, known as RNA interference, can also apply to other plants and insects. "Take your average corn plant that gets attacked by corn worms," said Baldwin. "You can use it to target any genes in an insect, and it's a clean and safe way to take care of the pests."

Hannah Burrack, associate professor of entomology at North Carolina State University, said that the idea of using RNA interference to make an insect more likely to be eaten is a new development. "We already have plants that are engineered to be insecticidal," she said. "The idea that RNA interference is affecting the next level up the food chain is novel."

But even though RNA interference has been successful in the lab, it's difficult to say how well it will do in the marketplace. "When you talk about these genetic engineering techniques, it can be a very time intensive and challenging prospect," said Burrack. "Sometimes it's straight forward, sometimes it's not."

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