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American Association for the Advancement of Science

When plants cry for help, predator bugs answer

A freshly hatched tobacco hornworm larva (Manduca sexta) is attacked by a predator bug of the genus Geocoris.
[Matthey Film]

Some plants have a really clever method for protecting themselves against pests. When caterpillars start nibbling on wild tobacco plants, their saliva cues a "help me!" signal from the plants that brings predatory insects flying in to the rescue, a new study shows.

The compounds that plants give off immediately upon damage are known as "green leaf volatiles," or "GLVs." If you've smelled freshly cut grass, you've smelled GLVs.

Two scientists, Silke Allmann of the Swammerdam Institute for Life Sciences in Amsterdam, Netherlands and the Max Planck Institute for Chemical Ecology in Jena, Germany and Ian Baldwin of the Max Planck Institute for Chemical Ecology, have discovered that these GLVs can send a very specific signal, at least in the case of the wild tobacco plant, Nicotiana attenuata.

Close-up view of a predatory bug of the genus Geocoris.
[Matthey Film]

They found that when these plants are attacked by tobacco hornworm caterpillars, Manduca sexta, the caterpillars' saliva causes a chemical change in the GLV compounds the plants had produced.

This modified cocktail of compounds then attract predatory "true bugs," Geocoris, which prey on hornworm eggs and young larvae, thus protecting the plant.

Although more research will be needed to figure out exactly how the molecules in the caterpillar saliva cause this change in the GLVs, it's clear that the caterpillars themselves cause the change in the GLV signal, the researchers say.


This research appears in the 27 August issue of the journal Science.