Copidosoma floridanum :

From:

And you thought your family was strange -- meet the wasp's

Bugs - Most larvae grow up feasting on caterpillar blood, then things get really weird

Wednesday, August 15, 2007

CARL ZIMMER

The Oregonian

To understand the rules that govern life, biologists often seek out the weird extremes. When it comes to family life, it's hard to find a stranger example than that of a common wasp, Copidosoma floridanum.

"You couldn't dream up a more surreal life cycle than these guys have," said Mike Strand, a University of Georgia professor.

Copidosoma floridanum, native throughout the United States, is a parasite. The female wasp lays one or two eggs inside the egg of the cabbage looper moth. As the host egg develops into a caterpillar, the wasp egg grows into a microscopic cluster of grapes.

Each grapelike mass of cells develops into a wasp embryo. A single egg can give rise to more than 3,000 genetically identical siblings, each about a fifth of an inch long. "The caterpillar is about 2 to 3 inches long, so you can stuff a lot of wasps in there," Strand said.

Most of the larvae are maggotlike creatures that drink the caterpillar's blood. But up to a quarter of the wasps take on an entirely different form. They develop slender, snakelike bodies and rasping jaws. Instead of slurping blood, these hundreds of soldiers attack other wasp larvae. "They just latch on and suck away," Strand said.

The bloodsuckers that are not killed by the soldiers eventually begin to devour the organs of their host, become pupae, and then develop into adults that fly away. The soldiers, on the other hand, cannot escape.

Biologists have known about Copidosoma floridanum's strange soldiers for more than a century, but they're enjoying a new surge of interest as a model that scientists can study to learn about the evolution of families.

"The big debate about these soldiers is what they're doing in their host," said Andrew Gardner, an evolutionary biologist at the University of Edinburgh.

Some of the evidence scientists have gathered suggests that soldiers exist to wipe out the competition. A cabbage looper often plays host to larvae from several wasp mothers. It can even carry larvae from other species of wasps. Soldiers kill off unrelated wasps, thus allowing their siblings to enjoy a bigger meal.

The soldiers themselves cannot reproduce. Yet natural selection might favor genes for these dead-end creatures. By killing off competitors, they increase the odds that their genetically identical siblings will survive and have offspring.

Strand and his colleagues have found that soldiers can tell the difference between their siblings and unrelated wasps -- a crucial skill for killing off rivals. On the other hand, soldiers sometimes kill members of their own family.

When a Copidosoma mother lays two eggs in a host, one egg produces thousands of males, the other thousands of females. The female soldiers will kill off many of their brothers.

Gardner and his colleagues recently built a mathematical model of Copidosoma floridanum's soldiers and blood-feeders to understand how this kind of fratricide might have evolved. While the soldiers are genetically identical to the sisters, they share only some of their genes with the males, which come from a separate egg.

That means the soldiers get a bigger evolutionary benefit from the success of their sisters than from that of their brothers. A few males are more than enough to fertilize thousands of female wasps. Any more males inside a host are just competition for the sisters.

©2007 The Oregonian

Not about Copidisoma floridanum,but another species: http://www.youtube.com/watch?v=vMG-LWyNcAs