Smell of Deceit: Species Trick Each Other with Odor

Researchers have recently made an unusual discovery that four species - all at different levels in the food chain - use the same single odor to communicate with and ruthlessly exploit each other.

The odor in question is methyl salicylate. Plant-feeding insects are often attracted to the odor, released by damaged plant tissue, because it's a signal that the origin is a good place to look for food, sexual partners, and egg-laying sites.

Damaged citrus trees release such an odor, which the jumping plant louse Diaphorina citri hones in on. Normally citrus tree sap is the only food of the young lice, but other species have evolved to take advantage of its attraction to methyl salicylate.

One of these is the bacterium Canditatus Liberibacter asiaticus, which infects citrus trees and forces them to release methyl salicylate to mimic an attack by plant lice. The jumping plant lice, expecting a safe haven and feeding frenzy, don't realize they are being duped - the bacterium zaps all nutrients from the citrus leaves.

This trick forces the lice to seek out another tree, this time with the bacterium hitching a ride on their body to infect other helpless trees.

Then there's the wasp Tamarixia radiata, which lays its eggs on young jumping plant lice, so that the wasp larvae can feed on them. To determine whether the odor attracted wasps as well, Lukasz Stelinski and University of Florida colleagues placed female wasps in an olfactometer, a device that gave wasps the choice of flying towards air containing methyl salicylate or to a control odor such as limonene, another compound produced by citrus trees.

Turns out these wasps indeed did like the methyl salicylate smell, meaning it finds its prey by essentially eavesdropping on the odor signal exchanged between bacteria, citrus trees, and plant lice.

"Communication between species is widespread in nature, but almost always involves only two or three species. Here, we show for the first time that the same signal connects four different species, each at a different level in the food chain. Through their separate evolutionary histories, they independently hit on the use of methyl salicylate as a way to take advantage of their prey," Stelinski said in a statement.

The findings were published in the journal Frontiers in Ecology and Evolution.