Saturday, August 22, 2009

virus benefits insect hosts

The Scientist | Bacteria-infecting viruses, generally thought to be harmful to their hosts, can also be surprisingly beneficial.

A bacteriophage infecting a bacterium living in the cells and body cavity of a small, plant-eating insect protects the insect from attack by a deadly wasp predator, reports a study published online in Science today (August 20). The discovery may help create more effective methods of pest control, the authors say.

"This is a wonderful paper," Christoph Vorburger, an ecologist at the University of Zurich, told The Scientist. "It is important because it shows clearly that genetic elements such as bacteriophages are vehicles for transmitting resistance to predators," added Vorburger, who was not involved in the study.

Small insects called pea aphids are parasitized by a species of wasp, Aphidus ervi. The wasp injects its eggs into the aphids, and the eggs develop, pupating and eventually killing the insects. Earlier work has shown that the symbiotic relationship between aphids and a species of bacteria called Hamiltonella defensa can keep the insect safe, but no one understood exactly how the bacterium offered protection.

Using genetic sequencing tests, Kerry Oliver from the University of Georgia and his colleagues determined that Hamiltonella harbors a bacteriophage. To find out whether the phage is what safeguards the insect, they then generated three aphid--lines one without the bacterium, one with the bacterium infected by the phage, and one with the uninfected bacterium. The team found that only aphids with the phage were protected from the wasps' egg.