Aphids and their symbiotic bacteria
Professor Charles Godfray’s group, co-lead with Dr Ailsa McLean, uses the pea aphid, an important insect pest, as a model system to investigate questions in evolution and ecology.
The group is particularly interested in symbiosis and the role which bacteria can play in the evolution of their insect hosts. Pea aphids host seven secondary symbionts: bacteria which are not essential for the aphid, but which live within specialised cells inside the aphid and which can have a number of important ecological effects on their hosts.
Each pea aphid individual has on average one or two different secondary symbionts, and understanding their distribution and ecological importance is a major part of this group’s research.
The group have carried out large scale surveys of symbiotic bacteria across multiple aphid species and populations. They perform experimental laboratory studies examining the effects of symbionts on the resistance of aphids to different natural enemies. They also carry out field experiments looking at the effects of symbiotic bacteria in aphids under natural conditions.
One large, worldwide survey examined 1,104 pea aphid clones, which exist as genetically differentiated races adapted to different host plants. This survey showed how the seven secondary symbionts are distributed geographically and ecologically: some symbionts are strongly associated with particular host-plant races, and others are found more frequently in particular environments.
Comparison of host and symbiont evolution show secondary symbionts are horizontally transmitted between pea aphid lineages and, more recent work shows, between different aphid species.
Symbionts (Buchnera aphidicola) within a bacteriocyte of a pea aphid (Acyrthosiphon pisum)
By J. White and N. Moran, University of Arizona, via Wikimedia Commons
The group demonstrated that possession of a symbiont called Regiella protected the aphid from attack by a fungal disease whilst colleagues in the United States showed a different symbiont provided protection against parasitoid wasps.
More recent experimental studies have demonstrated that a number of different, distantly related secondary symbionts are able to protect aphids from the same fungus (Pandora neoaphidis).
They have also demonstrated considerable genetic variation amongst strains of the same symbiont species: for example some strains of a symbiont called Hamiltonella provide protection against one parasitic wasp species but not another, with the opposite found in other strains, and still others provide no protection. Interestingly, aphid species that have a mutualistic association with ants (which protect them from parasitic wasps) are less likely to carry symbionts that perform the same function.
This is primarily fundamental research that aims to understand the relationship between aphids and their symbionts in different ecological contexts. However, since aphids are the single most important insect pests of temperate agriculture the group are alive to potential applications and frequently discuss their work with more applied scientists, for example at Rothamsted Research.
Aphids feeding on fennel by Fir0002 via Wikimedia Commons.
There are at least two potential avenues through which symbiosis research could be used to advance aphid pest control.
First, symbionts could be used to control crop pests directly, since secondary symbionts have the potential to spread through aphid populations. Symbionts could thus act as a drive mechanism to spread a novel trait within the aphid population. This technique is being trialled to interrupt the transmission of human diseases by mosquito vectors and might be used to control plant pests or to interrupt transmission of the diseases they vector.
Second, understanding the relationships between insect symbionts and natural enemies could improve biological control using those natural enemies. Farmers could choose the most appropriate control based on their particular crop and insect pest, and biological controls could be adapted to overcome the natural resistance provided by symbionts.
This research is funded by NERC & BBSRC
Photo of a pea aphid by Andy Murray on Flickr
Symbionts (Buchnera aphidicola) within a bacteriocyte of a pea aphid (Acyrthosiphon pisum) By J. White and N. Moran, University of Arizona, via Wikimedia Commons