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8-Oct-2004

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American Association for the Advancement of Science

When a virus is a wasp's best friend



Wasps cocoons on a tobacco hornworm. After completing their development within the host, Cotesia congregata larvae emerge and spin their cocoons on the back of the caterpillar. [Image Science]

Full size image available here

Caterpillars taste good -- if you're a growing wasp. New research shows how some mother wasps ensure that their babies get to feast on as many caterpillar meals as they like.

Scientists already know that some wasp mothers inject their eggs inside caterpillars. When the wasp eggs hatch, the babies eat their way out of the caterpillar -- growing bigger with each bite of caterpillar. The developing wasps, called "larvae," eventually squirm out of the caterpillar and spin cocoons on the caterpillars' backs. When the wasps emerge from the cocoon, they have wings.

Many of these caterpillars are pests that damage important crops, so sometimes farmers find the parasite wasps helpful for controlling the pests.



[Image Science]

Full size image available here

In the 08 October issue of the journal Science, French researchers look at a special weapon the wasps use against the caterpillars: a virus. Most humans don't want anything to do with viruses, which cause colds, stomach flu and serious illnesses. But for the wasps, viruses can really help out.

The viruses reproduce inside the wasp and then get injected into the caterpillar along with the wasps' eggs. The virus then interferes with the caterpillars' immune system and growth, making it easier for the wasp larvae to take over.

The wasps and the viruses have a relationship called "symbiosis," meaning each one helps the other in some way.

Eric Espagne of the Institut de Recherche sur le Biologie de l'Insect, CNRS in Evry, France and his colleagues studied the virus that a wasp called "C. congregata" injects into the tobacco hornworm. Specifically, they studied the sequence of the virus' genetic code, or "genome."

The genome turned out to be quite different from typical virus genomes, and the difference seems to be tied to the symbiosis between the wasp and virus. The scientists think both genomes have evolved together, as the two organisms developed their partnership.

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