Hornworm Caterpillar Uses Nicotine Breath
December 31, 2013

Caterpillar Uses Nicotine Breath To Ward Off Predators

Brett Smith for redOrbit.com - Your Universe Online

While e-cigarettes may have been all the rage in 2013, one cool cat(erpillar) doesn’t even need a mechanical smoking device to puff out clouds of toxic nicotine. The tobacco hornworm caterpillar is able to exhale this predator-repelling breath by re-purposing the nicotine it eats while feeding on a tobacco plant, according to a study published on Monday in the Proceedings of the National Academy of Sciences.

Nicotine actually acts as a defense mechanism for plants by targeting the nerve and muscle cells of animals. When a would-be predator starts eating the plant, nicotine in the consumed plant material begins to negatively affect the animal’s breathing and mobility.

“This is why nicotine is such a great defense for plants: it poisons everything that uses muscles to move, and since plants don’t have nerves or muscles, it doesn’t poison the plant,” study author Ian Baldwin, an ecologist at the Max Planck Institute for Chemical Ecology in Germany, told National Geographic.

The tobacco hornworm typically spends its day eating coyote tobacco plants, consuming the nicotine equivalent of one cigarette per day in the process. Immune to the effects of nicotine, the caterpillars store the drug in their blood and exhale it as a way to ward off wolf spiders, their chief predator.

Researchers from the Max Planck Institute began their study by placing nicotine breathing hornworms into plastic cups with wolf spiders. The spiders refused to eat any of the toxin-exhaling caterpillars.

"Spiders usually assess their prey after capture by tapping it with chemosensory endowed legs and palps," the study authors wrote. "Wolf spiders were clearly rejecting nicotine-fed larvae before penetrating their prey with their mandibles to inject their mixture of digestive enzymes and poisons."

Next, the researchers discovered that the caterpillars boosted their expression of a gut gene known as CYP6B46 after eating tobacco leaves, an indication that CYP6B46 was involved in the hornworm’s defenses against the drug.

To determine the gene’s true role, the researchers cultivated three different sets of nicotine plants. One set was modified to contain abnormally low levels of nicotine. The second set of plants was modified to produce a small chemical that would block the CYP6B46 gene. The third set of plants was used as a control group.

The study team discovered that the wolf spiders preferred to prey on the caterpillars that ate the nicotine-deficient tobacco or those that that ate the CYP6B46-blocking plants, compared to those that ate the control plants. The researchers’ further investigation showed that CYP6B46 transfers ingested nicotine from the bug’s stomach to the hemolymph, where it is exhaled.

The study authors noted that this isn’t the only incidence of an insect co-opting plant toxin for its own defense. One bug even uses a toxic puke to ward off enemies.

“The eastern tent caterpillar (Malacosoma americanum) regurgitates hydrogen cyanide and benzaldehyde ingested from their cyanide-containing host plants when attacked by ants,” they wrote.

The study results could eventually be used to either keep desirable bugs alive or make less desirable bugs more attractive to predators.