Bacteriophages Encode Factors Required for Protection in a Symbiotic Mutualism

Abstract

Attacks Wasps: The bacterium Hamiltonella defensa infects aphids and carries virulence determinants from a bacteriophage virus. Oliver et al. (p. 992 ) have now found that the toxin-bearing phage does not harm the aphid host of the bacterium, but targets the larvae of parasitoid wasps that infest the aphids. If an aphid population is not infested by wasps, the allied bacteriophage is shed by the bacterium, presumably because there is a cost to carrying it. If the wasps then resume their predation, the aphids are no longer protected and succumb to the parasitoid.