Look, we’re not saying smoking is good, but tobacco can confer the superpower of breath so toxic it keeps away spiders. Take a quick breath and come meet the tobacco hornworm, a caterpillar that has managed to hijack a plant’s defence system for itself.
Nicotine is a poison — in fact, poisonous enough to use as a pesticide and poisonous enough to use for murder. That’s why tobacco plants bother to make nicotine in the first place: to keep insects less industrious than the tobacco hornworm from chomping on its leaves. (Interesting, isn’t it, that humans have created a whole industry out of drugging themselves with nicotine, a social exposure to plant toxins.) To eat nicotine-filled plant leaves, tobacco hornworms first need to safely get rid of the poison in its waste — but it also keeps some of the nicotine as a special, nasty surprise.
In a paper published this week in the Proceedings of the National Academy of Sciences, scientists identify a interesting gene with a rather uninteresting name: CYP6B46. The gene lets the caterpillar take nicotine from its gut and put it into its hemolymph, or the blood-like fluid of an insect’s circulatory system. The caterpillar can then open breathing pores along its body and spray out nicotine, like a puff of the e-cigarette.
Cool party trick, but it gets better. The scientists also noticed that caterpillars raised on low-nicotine tobacco were surviving in lower numbers. Nicotine breath protected the caterpillars against predators, such as the wolf spider, which shrunk back at the toxic breath.
A wolf spider with a less fortunate caterpillar
The actual amount of nicotine the hornworm keeps for self-defence is very little, just 0.65 per cent of what they ingest, but that’s enough to create a concentrated spider-repelling spray. This caterpillar has not only neutralised the tobacco’s natural defence system, but also co-opted it for its own chemical warfare. What doesn’t kill the tobacco hornworm makes it stronger. [Not Exactly Rocket Science]
Pictures: Pavan Kumar