Friday, January 27, 2006

The Enemy of My Enemy is My Friend.

This maxim holds true in most parts of the world, including the plant and animal kingdoms. One of the really fascinating things about biology is the complex relationships that organisms develop with their environment, including the neighboring organisms with whom they share a common habitat.

Lest you think I’m engaging in anthropomorphism applying this saying to organisms other than humans consider the relationship between
Spodoptera littoralis,

Cotesia marginiventris,
and Zea mays.

In my opinion, that saying is a perfect summary of their relationship.

Spodoptera littoralis is a pest of many plants including corn. Adult females like the one pictured above lay their eggs on a wide variety of plants. When the larvae emerge they begin eating the host plant that their mother has chosen to be their meal. Plants being sessile, insentient, and generally lazy for that matter ;-) can do nothing to stop the attack by the hungry larvae and are eaten alive! Oh, the horror!

But, remember, plants have been on this planet for a mighty long time. And they wouldn't have lasted this long without a trick or two up their sleaves. One of those tricks is the production of secondary metabolites that can do a range of things such as make them taste bad to their insect attackers (not something we want to encourage in our crop plants), or those secondary metabolites can serve as a signal to other organisms that: "dinner is served". When corn plants are eaten by lepidopteran larvae (moth and butterfly catterpillars), they release a complex mixture of volatile compounds. These compounds attract the adult females of parasitic wasp species such as C. marginiventris.

These parasitic wasps attack the larvae and lay a single egg in the posterior of the catterpillar.
When the wasp egg hatches, the wasp larvae burrows inside the caterpillar's body and begins to chow down on the tasty parts inside. After the wasp larvae has eaten its fill, it burrows out of the caterpillar and forms a coccoon attached securely to the caterpillar's back, in which the wasp will pupate.

This takes about 7 to 10 days for C. marginiventris.

As you can see, the whole process leaves the caterpillar somewhat worse for wear.

This exit hole only tells part of the caterpillar's the tale of woe. Most of its internal organs have been eaten by the wasp and it will die in one day.

Now, scientists have identified the particular compound that attracts this wasp to corn plants that are being attacked by insect herbivores. And they have identified the single gene in corn that is responsible for producing this chemical distress signal, or dinner invitation depending on your point of view! The gene is a terpene synthase gene, tps10, which produces "(E)-beta-farnesene, (E)-{alpha}-bergamotene, and seven additional sesquiterpene hydrocarbons" in response to lepidopteran herbivory. When this gene was transferred into the model plant Arabidpsis thaliana, it produced the appropriate sesquiterpene compounds and served as an indirect defense of Arabidopsis against insect herbivory.

Interstingly, response to the sesquiterpenes produced by TPS10 appears to be a learned behavior in C. marniventris:
Indeed, females of this species are initially not attracted to these typical induced plant signals (18) but appear to exploit them as host location cues only after associating them with the presence of hosts during an initial oviposition event (19, 20).

The associative learning ability of C. marginiventris is a critical element of this tritrophic interaction, because parasitoids without oviposition experience were not significantly attracted (18). Because TPS10 products are the only sesquiterpene hydrocarbons specifically emitted after herbivory by lepidopteran larvae, they provide a very reliable cue to the parasitoid. Other hymenopteran parasitoids rely less strongly on learning and may employ more innate responses for host finding (19, 20).
"The enemy of my enemy is my friend." This is said to be an Arab proverb. How fitting then that the common name of Spodoptera littoralis is the Egyptian Cotton Leaf Worm.

The products of a single maize sesquiterpene synthase form a volatile defense signal that attracts natural enemies of maize herbivores

Christiane Schnee *, Tobias G. Köllner *, Matthias Held {dagger}, Ted C. J. Turlings {dagger}, Jonathan Gershenzon * and Jörg Degenhardt *, {ddagger}

*Max Planck Institute for Chemical Ecology, Hans-Knöll Strasse 8, D-07745 Jena, Germany; and {dagger}Laboratory of EvolutiRoundrock Journalonary Entomology, Institute of Zoology, University of Neuchatel, Emile-Argand 11-CP2, CH-2007 Neuchatel, Switzerland

The only blog inspired by a Bumper Sticker.

Update: The Circus of the spineless is up at Pharyngula. Apparently ,it is really for anything without a spine. I had thought it was just about invertebrates. Lots of good entries, I particularly like this magnificent Agrobacterium tumefaciens Crown Gall tumor submitted by Roundrock Journal.

Comments on "The Enemy of My Enemy is My Friend."


Blogger xenobiologista said ... (2/23/2009 10:43 AM) : 

The plot thickens. A lot of these parasitic wasps will inject the caterpillars with virus-like particles called polydnaviruses with circular DNA segments encoding virulence factors that help the larvae invade the caterpillar. The funny thing is that the PDVs don't encode any of their own structural proteins, so people didn't know where they were coming from...turns out the structural protein genes are integrated in the WASP's genome.


Anonymous Anonymous said ... (1/07/2010 2:17 AM) : 

I am contacting you on behalf of a French science centre based in Bordeaux, called Cap Sciences ( Our mission is to produce exhibitions and workshops to engage the general public, older and younger visitors, on subjects related to science and technologies. We are financed through public subsidies with one third of self-financing.
We are presently working on an exhibition on sustainable consumption which will open in February in Bordeaux. On such an essential issue, we are keen for the visitors to both feel and understand the impact of their choices in terms on consumption. We would like to show them examples of invasives species to approach that issue. This is why we are contacting as we would like to be able to use your photograph sodoptera littoralis
We believe the exhibition can make a significant difference in the public's attitude to consumption and participate in raising awareness on human impact on the planet. I do not unfortunately have an English version of the synopsis, but I would gladly send you the synopsis in French if you would like. For your information, the exhibition will be in Bordeaux until August and will then be presented in various French centres.
Thank you very much in advance for your interest and hopefully, for your collaboration to our project.
Please copy your response to Nathalie Caplet, in charge of scientific and cultural ressources for Cap Sciences (; Tel +33 55 57 85 51 37). Thank you.
Yours sincerely
Amélie Herpin


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