Plants smell different when attacked by exotic herbivores

January 24, 2017, Radboud University
Plants smell different when attacked by exotic herbivores
Credit: Radboud University

A new study to be published in the scientific journal New Phytologist reveals that plants' odour bouquet changes depending on the type of enemy that attacks it. To the surprise of the researchers involved, native plants emit a special odour bouquet when they are attacked by exotic herbivores.

Plants emit odours to call in reinforcements; for example, to let a parasitic wasp know that a caterpillar is present. This may not help the plant immediately, but in the long run, it means fewer butterflies and voracious caterpillars in the next generation. Dutch field mustard (Brassica rapa) emits different odour bouquets in response to exotic as opposed to native caterpillars, slugs and aphids.

Test with twelve herbivores

Biologists from Radboud University and the University of Neuchâtel in Switzerland tested the effects of twelve types of , including specialists and generalists, sucking and chewing herbivores and exotic and native herbivores. It included a wide range of very different herbivores ranging from cabbage aphids and small whites to green peach aphids and a slug. The researchers, including Nijmegen physicist Simona Cristescu, identified subtle differences in the odours emitted by using a gas chromatograph with a highly accurate mass spectrometer at the Department of Organic Chemistry.

"We used clever statistical models and calculations to identify the complex combinations of volatile substances induced by the different groups of herbivores," says Nicole van Dam, professor of Plant-Insect Interactions at Radboud University's Institute for Water and Wetland Research (IWWR) and the German Institute for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig.

Plants smell different when attacked by exotic herbivores
Credit: Radboud University
Are you a naturalised insect?

"We were debating whether two species of caterpillars, the beet armyworm (Spodoptera exigua) and the cabbage looper (Trichoplusia ni), were to be considered exotic or whether they were naturalised species. These species have been observed in the Netherlands, particularly in greenhouses, but they do not overwinter outside here. The odour bouquets emitted by wild field mustard plants after feeding by the two herbivores left no room for doubt: this is definitely an exotic species. Our statistical models can therefore be used to determine the status of the herbivorous insect based on the herbivore induced odour bouquet."

Exotic and native species were not defined by a single volatile substance, but by the ratio of volatiles they produced. "This is consistent with what we know about the perception and behaviour of parasitic wasps and other predators. They use the bouquet of odours released by the plant to obtain information about their prey."

Communicating plants

Van Dam sees the results as "spectacular proof" of how specific plants respond to their environment. "They may not have a nervous system, eyes, ears, or mouths, but they are capable of determining who is attacking them. Based on this, they can transmit reliable information to parasitic wasps. What I find truly amazing is that they're even capable of distinguishing between a native and an exotic herbivore."

Climate change and globalisation have helped to introduce an increasing number of exotic herbivores to the Netherlands. This can disrupt existing interactions between plants, herbivores and parasitic wasps. "Our initial idea was that the new odour bouquets emitted by plants when they are attacked by exotic herbivores may confuse parasitic wasps," explains Van Dam. "This may reduce the effectiveness of biological pest control. Our research suggests that endemic can learn to avoid these plants by identifying differences in odours."

Explore further: Butterfly eggs alert mustard plant to voracious caterpillars

More information: Herbivore-induced plant volatiles accurately predict history of coexistence, diet breadth, and feeding mode of herbivores. New Phytologist, 2017. DOI: 10.1111/nph.14428

Related Stories

Using different scents to attract or repel insects

March 31, 2014

Flowering plants attract pollinating insects with scent from their flowers and bright colours. If they have become infested with herbivores like caterpillars, they attract beneficial insects like parasitic wasps with the ...

The hungry caterpillar: Beware your enemy's enemy's enemy

November 27, 2012

When herbivores such as caterpillars feed, plants may "call for help" by emitting volatiles, which can indirectly help defend the plants. The volatiles recruit parasitoids that infect, consume and kill the herbivores, to ...

Mustard plants have double defence against insect pests

August 14, 2014

Mustard plants have a double line of defence against foraging insects. The plants can release odours to attract miniscule wasps, which parasitise insect pest eggs. However, mustard plants also react by allowing cells to die, ...

Recommended for you

Loss of a microRNA molecule boosts rice production

October 16, 2018

The wild rice consumed by our Neolithic ancestors was very different from the domesticated rice eaten today. Although it is unclear when humans first started farming rice, the oldest paddy fields—in the lower Yangzi River ...

Big Agriculture eyeing genetic tool for pest control

October 16, 2018

A controversial and unproven gene-editing technology touted as a silver bullet against malaria-bearing mosquitos could wind up being deployed first in commercial agriculture, according to experts and an NGO report published ...

A selfish gene makes mice into migrants

October 16, 2018

House mice carrying a specific selfish supergene move from one population to another much more frequently than their peers. This finding from a University of Zurich study shows for the first time that a gene of this type ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.