Bad breath is no stranger to many animals, but tobacco hornworm caterpillars take it to another level with what researchers are calling “toxic halitosis.”
The caterpillars feast on tobacco plants, ingesting large amounts of nicotine as they do so. A study in the latest Proceedings of the National Academy of Sciences found that the caterpillars retain nicotine toxin in their blood that they puff out as a noxious warning to would-be predators.
Insects have long used plant toxins for their own benefit. There’s even a caterpillar with toxic barf.
As lead author Pavan Kumar and his team explain, “The eastern tent caterpillar (Malacosoma americanum) regurgitates hydrogen cyanide and benzaldehyde ingested from their cyanogenic (i.e. cyanide-containing) host plants when attacked by ants.”
Both of these compounds are poisonous, as mystery book readers likely know. Poisonous puke is obviously not very appealing, even to voracious ants, so the eastern tent caterpillar’s defense mechanism often works.
The Atala butterfly (Eumaeus atala) also acquires a toxic substance from plants that turns off bird and ant predators. Rattlebox moths ingest alkaloids that are poisonous to spiders, which then steer clear of the moths.
In the case of the tobacco hornworm caterpillar, Kumar and his colleagues from the Max-Planck-Institute for Chemical Ecology found that wolf spiders, which usually consider the caterpillars to be good eats, avoid them if they puff out nicotine.
Nicotine is a natural toxin. In humans, as for other creatures, it can be deadly, although it usually takes a lot for a person to succumb to its effects. For example, two brothers died after smoking 17-18 pipes full of tobacco. Health problems can also result if someone touches wet tobacco leaves. Nicotine can absorb into the body, causing everything from nausea to dizziness.
The caterpillars, on the other hand, possess a gene that allows them to shunt nicotine into external respiratory openings known as spiracles. It is through these “breath holes” that the caterpillars release their toxic halitosis.
The scientists used genetic engineering to create tobacco plants that would silence the gene that would otherwise be turned on by ingested nicotine. As expected, wolf spiders wolfed down the caterpillars left without the truly bad breath.
Such findings open the door to creating genetically engineered plants that are better able to withstand insect predators. The research might enable scientists to make bugs more appealing to predators, letting nature take its course without the need of insecticides. The GMO component, though, will be a hard sell to those hoping to avoid genetically modified organisms.
Image: Daniel Schwen, Wikimedia Commons