Bacterial Symbiont Protects Aphid from Lethal Fungal Pathogen

Claire Scarborough, Julia Ferrari and Charles Godfray demonstrated that a bacterium that lives inside an aphid protects its host from a fungal pathogen. Their work has been published in Science on 16th December.

A study on the effects of facultative endosymbiont on the ecology of their hosts has been published in Science on 16th December. Claire Scarborough, Julia Ferrari and Charles Godfray demonstrated that a bacterium that lives inside an aphid protects its host from a fungal pathogen.

Bacterial endosymbionts are widespread in insects, but their effects on the host are often unknown. The paper reports on impacts of the bacterium Regiella insecticola (aka U-type, PAUS) on its host, the pea aphid Acyrthosiphon pisum . Some genotypes of the aphid harbour the facultative symbionts, while others do not. The research team used this and injected aphid body fluids containing the bacteria into aphids that were free of them. After a few ge nerations, when these artificial infections had established, they exposed the aphids with Regi ella and uninfected controls to the fungus Pandora neoap hid is. This fungus usually grows inside the aphid and kills within a few days. However, aphids carrying Regiella were killed s ignificantly less often by the fungus than aphids without this symbiont. Moreover, the cadavers of the aphids that succumbed to the fungus often produced no infectious spores and thus prevented the pathogen from spreading and infecting nearby aphids. Aphids in the vicinity of a diseased individual are likely to be closely related to the dead individual and the symbiont therefore not only increases an aphids’ individual but also its inclusive fitness in the presence of the pathogen.

An on-line version of this paper can be found on the Science web site.