Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Lethal Backfire: Green Odor with Fatal Consequences for Voracious Caterpillars

The dilemma for tobacco hornworm larvae: By feeding on tobacco leaves they unintentionally and rapidly transform plant substances into attractant signals that betray their location to their own natural enemies - with lethal consequences.

During field studies, scientists at the Max Planck Institute for Chemical Ecology discovered that the oral secretions of tobacco hornworm larvae (Manduca sexta) contain a particular substance that promptly alters a green leaf volatile in tobacco leaves into an odor attractant signal. With this signal, called (E)-2-hexenal, they unintentionally lure their own enemies: carnivorous bugs. These bugs start their piercing attacks not only against freshly hatched caterpillar babies; they also devour eggs laid by the female moths. (SCIENCE, August 27, 2010)

Experimental setup in the field: eggs, a young caterpillar and a predatory bug that has just arrived, all are located on the bottom of the tobacco leaf. MPI chemische Ökologie / Danny Kessler

A freshly hatched tobacco hornworm larva (Manduca sexta) is attacked by a predatory bug of the genus Geocoris. Only a few hours before, the feeding caterpillar had – catalyzed by a substance in its oral secretion – changed the chemistry of the plant’s “green” odor in such a way as to produce the new odor which attracts its own enemy; the change is to the plant’s advantage as it has lethal consequences for the caterpillar. Matthey Film

Plants have developed a sophisticated defense system. They can not only directly fend off herbivores by producing toxins, but also do so indirectly by emitting odorant molecules into the atmosphere that are perceived by predatory insects; these predators are lured to the attacked plant and feed on the herbivore or parasitize it – thereby providing a benefit for the plant.

Since the discovery of indirect defense strategies in plants, ecologists have been interested in the molecular mechanisms and the course of events underlying them. For example, almost all plants switch on some of their defenses only when an herbivore is actually attacking them. But how does the plant recognize the attack from the herbivore? “The plant cannot see its attacker, but plants can sense the digestive substances that attacking larvae have in their oral secretions when these substances come into contact with the leaves,” Silke Allmann, PhD student from Dortmund in the Department of Molecular Ecology, headed by Prof. Ian Baldwin, assumes. Ian Baldwin’s department is looking for plant substances, signal transduction chains and metabolic pathways after herbivore attack.

Recently, the scientists’ attention was drawn to substances in tobacco plants called “green leaf volatiles” (GLV); GLV are compounds released by plants after mechanical damage. These molecules are responsible for the typical smell of freshly cut grass. Last year the green odorant substances of tobacco were examined more carefully. The scientists found that the amount of a certain GLV, namely (E)-2-hexenal, suddenly increased after oral secretions of Manduca sexta larvae had been applied on wounded leaves. In tobacco plants the aldehyde, hexanal, is present in two isomeric forms: (Z)-3-hexenal and (E)-2-hexenal. Z-E conversions can be catalyzed by specific enzymes, so-called isomerases. “We supposed that the increased occurrence of (E)-2-hexenal may attract the carnivores, because we always discovered Geocoris when young Manduca larvae had just hatched and started feeding on the tobacco leaves,” says Ian Baldwin.

To test this assumption, the researchers started a series of experiments using Manduca sexta eggs and different blends of (Z)-3-hexenal and (E)-2-hexenal. The eggs were glued to tobacco plants growing in the field and different mixtures of odorant signals were applied to adjacently located cotton swabs. After 12 and 24 hours, the fate of eggs on the leaves was determined. The result: Plants that had been perfumed with the Z-lure had only 8% of their glued eggs attacked, whereas plants perfumed with the E-lure had lost 24% of the eggs. And the eggs had been eaten by Geocoris. The speed of plants’ defense triggering was particularly impressive: it takes less than an hour to trigger the conversion of the Z-lure to the E-lure and less than 24 hours for the predation of the eggs. “Other indirect defense mechanisms of plants require the activation of new metabolic pathways for the release of odorant signals, and these responses are much slower,” says Ian Baldwin. The release of (E)-2-hexenal after its rapid and simple conversion from (Z)-3-hexenal is so rapid that it provides the prey-searching predator with enough information to pinpoint the exact location of the feeding herbivore on a plant. And it is this information which makes the release of volatile “alarm calls” an effective defense strategy for plants.

But which substance is betraying the caterpillar? “The simplest assumption is that the larval oral secretions contain a special enzyme, probably an isomerase, which rearranges the Z:E ratio of the aldehyde in favor of (E)-2-hexenal,” says Silke Allmann. To test this assumption, the oral secretion was briefly heated and subsequently applied on wounded leaves. (E)-2-hexenal was now no longer produced. Hence, the unknown substance is likely an enzyme, because enzymes are typically heat labile. The scientists also determined whether tobacco plants react specifically on Manduca sexta oral secretions or to secretions of other larval species as well. Interestingly, the secretions of two Spodopera species (Spodoptera exigua and S. littoralis) had significantly lower effects.

However, one question remains unanswered: Why does the oral secretion of Manduca sexta larvae contain a substance which endangers the larvae’s lives as soon as they start feeding on tobacco leaves? Silke Allmann and Ian Baldwin hypothesize that the production of (E)-2-hexenal protects the larvae against other untested attackers, such as bacteria. Harmful microorganisms, consumed by the larvae every day in large amounts together with the leaf tissue, may be killed quickly and effectively by (E)-2-hexenal, which is known to be a strong antibiotic agent. Hence the detrimental aspects of producing (E)-2-hexenal, that of betraying the precise location of the Manduca sexta larvae to their enemies, may be balanced by the benefits of fewer bacterial infections.

Regardless, the winner in this tritrophic food chain is the carnivore Geocoris, which is well fed as a result of the response – thanks to its highly sensitive antennae which enable it to smell the slightest concentrations of (E)-2-hexenal. [JWK, AO]

Original Publication:
S. Allmann, I. T. Baldwin: Insects betray themselves in nature to predators by rapid isomerization of green leaf volatiles. SCIENCE, DOI: 10.1126/science.1191634
Further Information:
Ian T. Baldwin, Max Planck Institute for Chemical Ecology, Hans-Knöll-Straße 8, 07745 Jena, Germany. Tel.: +49 (0)3641- 57 1101, Mobile: +49 (0)175 180 4226;

Silke Allmann, Max Planck Institute for Chemical Ecology, Hans-Knöll-Straße 8, 07745 Jena, Germany. Mobile: +31 (0)624 356988;

Picture Requests:
Angela Overmeyer, Max Planck Institute for Chemical Ecology, Hans-Knöll-Straße 8, 07745 Jena, Germany. Tel.: +49 (0)3641- 57 2110;

Dr. Jan-Wolfhard Kellmann | Max-Planck-Institut
Further information:

More articles from Life Sciences:

nachricht Make way for the mini flying machines
21.03.2018 | American Chemical Society

nachricht New 4-D printer could reshape the world we live in
21.03.2018 | American Chemical Society

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

TRAPPIST-1 planets provide clues to the nature of habitable worlds

21.03.2018 | Physics and Astronomy

The search for dark matter widens

21.03.2018 | Materials Sciences

Natural enemies reduce pesticide use

21.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>