Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Beetles that taste like mustard - Flea beetles outwit their host plant’s mustard oil bomb

08.05.2014

Flea beetles are important pests of cabbage and other cruciferous plants. These plants use a sophisticated defense system, known as the mustard oil bomb, to get rid of their enemies : If plant tissues are wounded, glucosinolates and an enzyme known as myrosinase come into contact, and, as a result, toxic metabolites are formed which deter most insects. This defensive mechanism, however, has no negative effect on flea beetles, according to scientists from the Max Planck Institute for Chemical Ecology. Flea beetles are even able to sequester glucosinolates. Moreover, the insects use their own myrosinase and can utilize the plants’ defensive chemicals for their own purposes.

Almost all herbivorous insects are specialized to feed on specific host plants and have adapted to their chemical defenses. Flea beetles are important pests of cabbage and other cruciferous plants, such as mustard, horseradish and rapeseed. These plants use a sophisticated defense system, known as the mustard oil bomb, to get rid of their enemies :


A striped flea beetle (Phyllotreta striolata) is feeding on celery cabbage leaves (Brassica rapa). The pest insect causes major damage on young cruciferous plants.

Christian Ulrichs / Humboldt-Universität zu Berlin


Although Phyllotreta beetles damage plant tissues with their mandibles, the plants’ defense mechanism in the form of the mustard oil bomb is not activated.

Christian Ulrichs / Humboldt-Universität zu Berlin

If plant tissues are wounded, glucosinolates and an enzyme known as myrosinase come into contact, and, as a result, toxic metabolites are formed which deter most insects. This defensive mechanism, however, has no negative effect on flea beetles, according to scientists from the Max Planck Institute for Chemical Ecology in Jena, Germany.

Flea beetles are even able to sequester glucosinolates without the mustard oil bomb being set off by the plant’s enzyme. Moreover, the insects use their own myrosinase and can utilize the plants’ defensive chemicals for their own purposes. The beetles’ mustard oil bomb is likely to fend off predators. (Proceedings of the National Academy of Sciences of the USA, May 2014, doi: 10.1073/pnas.1321781111)

Plants defend themselves against herbivores by employing a large arsenal of chemical substances, so-called secondary metabolites. In return, many insects have counter-adapted to plant defenses and can feed on their host plants without any problems. The “arms race” between plants and insects is behind the amazing variety of different species; variations emerged in the course of co-evolution of those two major groups of organisms. Some insects − leaf beetles or tobacco hornworms, for example − even utilize plant metabolites for their own defenses.

Franziska Beran, head of the research group “Sequestration and Detoxification in Insects” at the Max Planck Institute for Chemical Ecology in Jena, Germany, and her colleagues study flea beetles (Phyllotreta). The small pest insects, whose name refers to their impressive jumping ability, prefer to feed on the young leaves of all cabbage species and their method of feeding causes a characteristic pitting damage. They are despised by gardeners and farmers.

Before she started working on her PhD project at the Berlin Humboldt University, the young scientist completed an internship at the AVRDC-The World Vegetable Center in Taiwan, where she first learned about the devastating damage this beetle species causes on cabbage cultures in Southeast Asia. Her PhD thesis focused on how the insects aggregate and she asked if they use pheromones and plant odors as olfactory cues. She found out that male flea beetles emit a pheromone that attracts conspecifics; however, the attraction occurs only in conjunction with plant volatiles. At the core of her analyses were the degradation products of glucosinolates, plant metabolites that are responsible for the all-too-familiar smell of cabbage.

For their current project, the scientists compared glucosinolates in the host plants to the volatile degradation products that are formed when beetles feed on the plants, damaging plant tissues. The plant defense mechanism − called the mustard oil bomb because the degradation products that are formed are toxic − consists of two components: the glucosinolate and the activating enzyme myrosinase. Usually, the glucosinolate-myrosinase system is a highly efficient defense strategy cabbage plants deploy to deter herbivores. However, it does not repel the flea beetles, which readily infest the plants. Analyses showed that volatile degradation products were present when plants were infested with flea beetles, but the substances were not emitted by the plants.

It appeared that the flea beetles themselves were emitting the volatile glucosinolate metabolites. Further experiments revealed that flea beetles can take up and store an amount of glucosinolates equivalent to almost 2% of their own body weight. Although cabbage plants contain a large variety of different glucosinolates, the beetles sequester only some of them. Franziska Beran made a surprising conclusion: “The beetles have evolved their own activating myrosinase which specifically hydrolyzes the glucosinolates which they have sequestered from the plants.”

The research results indicate that flea beetles not only survive the cabbage plants’ mustard oil bomb unscathed, the insects even utilize selectively sequestered glucosinolates for their own purposes. Aphids are known to deploy a similar strategy. However, unlike aphids, which suck the phloem by tapping individual plant cells, flea beetles are chewing insects that wound leaf tissues. Such wounding should activate the mustard oil bomb but does not. Why this is the case and why flea beetles are able to sequester intact glucosinolates is still a mystery. Somehow the insects manage to inactivate the plant’s myrosinase.

The researchers want to find out where the beetles store the glucosinolates, how they control their own mustard oil bomb, and why they can hydrolyze glucosinolates without being poisoned by the resulting degradation products. Particularly interesting is the question: Why do the insects sequester glucosinolates and how do they control glucosinolate hydrolysis with their own enzyme? “On the one hand, either the glucosinolates or their degradation products may play an important role in the beetles’ communication with conspecifics.

On the other hand, they may have a specific function in the insects’ defense against their own enemies,” Franziska Beran hypothesizes. She also wonders about the beetle larvae which live underground and feed on roots. They are exposed to many predators and pathogens and a good chemical defense is definitely advantageous.

Behavioral studies will now also be used in order to elucidate the ecological function of glucosinolate sequestration in flea beetles. Better understanding of insect adaptation to plant chemical defenses will likely contribute to better control of mass occurrences of agricultural pests that are a major problem worldwide. [AO/FB]

Original publication:
Beran, F., Pauchet, Y., Kunert, G., Reichelt, M., Wielsch, N., Vogel, H., Reinecke, A., Svatoš, A., Mewis, I., Schmid, D., Ramasamy, S., Ulrichs, C., Hansson, B. S., Gershenzon, J., Heckel, D. G. (2014). Phyllotreta striolata flea beetles utilize host plant defense compounds to create their own glucosinolate-myrosinase system. Proceedings of the National Academy of Sciences of the United States of America. doi: 10.1073/pnas.1321781111
http://www.pnas.org/cgi/doi/10.1073/pnas.1321781111

Further information:
Dr. Franziska Beran, Max Planck Institute for Chemical Ecology, Hans-Knöll-Straße 8, 07745 Jena. Tel. +49 3641 57-1553, E-Mail fberan@ice.mpg.de

Contact and picture requests:
Angela Overmeyer M.A., Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07743 Jena, +49 3641 57-2110, overmeyer@ice.mpg.de

Download of high resolution images via http://www.ice.mpg.de/ext/735.html

Weitere Informationen:

http://www.ice.mpg.de/ext/1105.html?&L=0

Angela Overmeyer | Max-Planck-Institut

More articles from Life Sciences:

nachricht New Computer Model Could Explain how Simple Molecules Took First Step Toward Life
29.07.2015 | Brookhaven National Laboratory

nachricht Switch for building barrier in roots
29.07.2015 | The University of Tokyo

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Superfast fluorescence sets new speed record

Plasmonic device has speed and efficiency to serve optical computers

Researchers have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second and could form the basis of optical computing.

Im Focus: Unlocking the rice immune system

Joint BioEnergy Institute study identifies bacterial protein that is key to protecting rice against bacterial blight

A bacterial signal that when recognized by rice plants enables the plants to resist a devastating blight disease has been identified by a multi-national team...

Im Focus: Smarter window materials can control light and energy

Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.

By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for...

Im Focus: Simulations lead to design of near-frictionless material

Argonne scientists used Mira to identify and improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity at the macroscale for the first time. Argonne Leadership Computing Facility (ALCF) researchers helped enable the groundbreaking simulations by overcoming a performance bottleneck that doubled the speed of the team's code.

While reviewing the simulation results of a promising new lubricant material, Argonne researcher Sanket Deshmukh stumbled upon a phenomenon that had never been...

Im Focus: NASA satellite camera provides 'EPIC' view of Earth

A NASA camera on the Deep Space Climate Observatory (DSCOVR) satellite has returned its first view of the entire sunlit side of Earth from one million miles away.

The color images of Earth from NASA's Earth Polychromatic Imaging Camera (EPIC) are generated by combining three separate images to create a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

3rd Euro Bio-inspired - International Conference and Exhibition on Bio-inspired Materials

23.07.2015 | Event News

Clash of Realities – International Conference on the Art, Technology and Theory of Digital Games

10.07.2015 | Event News

World Conference on Regenerative Medicine in Leipzig: Last chance to submit abstracts until 2 July

25.06.2015 | Event News

 
Latest News

A New Litmus Test for Chaos?

29.07.2015 | Physics and Astronomy

New Computer Model Could Explain how Simple Molecules Took First Step Toward Life

29.07.2015 | Life Sciences

New ERC calls published under Horizon 2020

29.07.2015 | Awards Funding

VideoLinks
B2B-VideoLinks
More VideoLinks >>>