Plants Smell Different When They Are Eaten By Exotic Herbivores

 

When they are attacked by herbivores, many plants call in reinforcements. To this end, they emit odours. These odours attract wasps, for example, that are parasites and in search for host animals. The wasps lay their eggs into the caterpillars, thereby killing them: This means fewer butterflies and voracious caterpillars in the next generation. An international research team has tested the effects of twelve types of herbivores on field mustard (Brassica rapa). The researchers found that the plants consistently adapt the odours they emit upon attack to the characteristics of the respective herbivore. This helps the plant to specifically attract natural enemies that feed on the herbivores eating them. Most surprisingly, they emit different odour bouquets in response to exotic as opposed to native herbivores.

 

 

Among the twelve different herbivores tested were caterpillars, aphids and even a slug, and the herbivore selection included specialist and generalist, sucking and chewing, as well as exotic and native species. The researchers identified subtle differences in the odours emitted by the mustard plants using a gas chromatograph with a highly accurate mass spectrometer. They found that the reactions to exotic and native herbivore species were not defined by a single volatile substance, but by the ratio of different volatiles. "This is consistent with what we know about the perception and behaviour of parasitic wasps and other predators. They use a bouquet of odours released by the plant to obtain information about their prey," says study leader Nicole van Dam, who is a professor at the German Centre for Integrative Biodiversity Research (iDiv) and the Friedrich Schiller University Jena (Germany). She is also affiliated with Radboud University (Netherlands), where two of the other study authors work and were the research was carried out.