Aphid killing bacteria: how do they work and how can we utilize them?

Insecticide resistance and on-going legislation changes on the use of insecticides are likely to reduce its availability for use in agriculture; hence there is an urgent need to develop effective biological controls against these pests. From this perspective, the interactions between insects such as aphids and microorganisms could be of crucial importance as it could lead to the discovery of biological molecules that can be used for the control of insects. Recent findings showed that phylloplane bacteria can kill insects with negligible evidence of mammalian toxicity and thus act as novel biocontrol agents. To examine the effect of bacterial pathogens on aphid mortality, an artificial feeding system with a liquid diet was established to devise a high-throughput screening system to identify pathogenic bacteria against the Green Peach Aphid Myzus persicae (“wild type” susceptible clone plus insecticide resistant clones). Six bacterial strains were pathogenic to all insecticide susceptible and resistant clones although variation in susceptibility was observed. No single bacterial strain was identified that was consistently more toxic to insecticide resistance clones than susceptible clones, suggesting there was no penalty in resistant clones that makes such clones less fit to bacterial challenge. RNASeq was used to examine changes in aphid and bacterial gene expression during early stage infection. The altered transcript profiles revealed stress and cell morphogenesis genes in aphids and osmoregulation, stress and efflux transporter genes in bacteria that were differentially expressed. These data are being used to understand the molecular basis of aphid mortality to bacteria infection and to assess the risk of use and likelihood of aphid resistance occurring.