Tobacco-eating caterpillar uses nicotine as defence

Scientists have discovered that a bizarre tobacco-eating caterpillar puffs out nicotine to ward off predators.
Researchers found that a gene in hornworm caterpillars allows them to puff nicotine out through their spiracles (tiny holes in their sides), from the tobacco they consume, as a warning to their would-be predators such as wolf spiders.
"It's really a story about how an insect that eats a plant co-opts the plant for its own defence," said study researcher Ian Baldwin, a professor at the Max Planck Institute for Chemical Ecology in Germany.
The researchers discovered this tactic called "defencive halitosis" when trying to find out how hornworm caterpillars could consume tobacco plants despite the toxic nicotine within the plant's tissues.

By feeding hornworm caterpillars tobacco plants with and without nicotine, researchers identified the gene that was activated when the caterpillars consumed nicotine-containing tobacco plants.
The scientists then placed so-called interference RNA matching that gene in tobacco plants grown in the lab. The interference RNA targeted that gene, preventing the caterpillars from using their defence, 'LiveScience' reported.

When caterpillars consumed the gene-altered tobacco, they lost their ability to produce the tobacco halitosis and thus their ability to ward off wolf spiders.
As a result, they were consumed at a higher rate by wolf spiders, a rate similar to that found for caterpillars consuming nicotine-depleted tobacco plants.

While the study involved wolf spiders, the nicotine halitosis does not necessarily turn away other predators. This defence, Berenbaum noted, has the advantage of warning a predator of a prey's toxicity without requiring the prey to lose a limb.
The study is published in the Proceedings of the National Academy of Sciences.