How Plants Summon Insect Armies to Defend Themselves From Attackers

An international team of scientists has found that plants have the ability to determine what specific kind of predator is attacking them (trees can even identify deer by their saliva), and then release special cocktails of odors to attract that predator's enemies. Even more surprising, the plants they studied were even able to recognize the difference between their native enemies and introduced, exotic ones. The study was published on Tuesday in New Phytologist.

In the study, scientists looked at how field mustard responded to about 12 different attackers. Caterpillars, aphids and slugs slimed and crawled their way around the mustard plants, slicing, sucking and chewing up leaves. For each aggressor, the mustard plant discharged a distinct bouquet of odors designed to alert the attackers' natural enemy insects.

These insects  have learned that the odors mean food or hosts for their larvae. When parasitic wasps get a whiff of a certain odor profile, for example, they fly to the besieged plant and are gifted with caterpillars that they can inject their eggs into and zombify.

"The plants may not have a nervous system, eyes, ears, or mouths, but they are capable of determining who is attacking them," said study leader Nicole van Dam, from the German Center For Integrative Biodiversity Research (iDiv) in a public statement.

Shockingly, scientists also found that the mustard plants they studied were capable of recognizing exotic and invasive species as dark horses, and they could create  novel odor profiles to match them. "What I find truly amazing is that they're even capable of distinguishing between a native and an exotic herbivore," van Dam said in the same public statement.

If the invasive attacker doesn't have any natural predators in that environment, however, then it could be all for naught.

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