Pity the tobacco hornworm caterpillar, which appears to have been outsmarted by its favourite food. Every time it feasts on tobacco leaves, it inadvertently converts molecules released by the plant into chemicals that call in the predatory big-eyed bug.
Like many plants, when tobacco is damaged – by hungry herbivores or otherwise – it gives off chemicals called green leaf volatiles (GLVs). These "SOS molecules" protect the plant by attracting predators that eat herbivores.
Ian Baldwin of the Max Planck Institute for Chemical Ecology in Jena, Germany, and colleagues have now discovered that the mix of GLVs produced by a tobacco plant damaged by a caterpillar and one damaged in the absence of caterpillars were subtly different.
When they released the two mixes in a field, the one that had been produced in the presence of a caterpillar attracted more big-eyed bugs. Chemical analysis revealed that the caterpillar's saliva reacts with the plant's pure GLVs to produce the more attractive version of the chemicals.
"In effect, the caterpillar calls the police on itself," says Baldwin. He suggests that crops could be genetically modified to release the improved signal as a defence against pests.
Journal reference: Science, DOI: 10.1126/science.1191634