Trees call for help from birds and predatory insects

Forest trees emit scents when attacked by caterpillars and other herbivores. They use these to attract predatory insects and even birds, thus getting rid of their pests. This had only been demonstrated in laboratory or garden experiments so far. A team of researchers led by Martin Volf from the Biology Centre of the Czech Academy of Sciences, could now demonstrate this phenomenon for the first time in a natural habitat – in the 40-metre-high canopy of the Leipzig floodplain forest.

The chemical calls for help are so effective that they significantly determine the composition of the insect community in the canopy. This knowledge could be used in future for natural pest control in agriculture and forestry, the researchers write in the journal Ecology Letters.

Like a human fingerprint, each tree species emits its very own bouquet of volatile organic compounds (VOC). Animals learned to read this pattern in the course of evolution; leaf-eating insects find their host trees this way. But the trees are not helplessly at their mercy; they defend themselves: e.g., they produce bitter substances, which the herbivores do not like. In addition, the trees release particular VOCs to put different parts of the plant on the alert. In this way, however, they also attract other animals such as birds and predatory insects, which have also learned to read the VOC's meaning. They come flying to devour the tree's "pests". From the trees' perspective, evolution has provided them with a kind of "emergency call".

"The fact that plants can chemically attract parasitic wasps, predatory bugs and even birds when attacked by pests had been known for some time," says first author Dr Martin Volf from the Biology Centre of the CAS, who led the study. "However, this defence mechanism has never been tested for adult trees in a realistic environment so far. This was made possible by a combination of research methods, from animal behaviour experiments at the height of 40 metres on iDiv's Leipzig Canopy Crane to chemical analyses of plant scents through metabolomics," says the biologist. Metabolomics systematically study the unique chemical fingerprints that specific cellular processes leave behind.

Read the full press release here.

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