D3382: Virulence of diverse Pseudomonas strains to pea aphids

Aphids are worldwide agricultural pests that feed on plant sap and can transmit plant pathogens to surrounding plants. Pseudomonas syringae, a plant epiphyte, can infect these pests pathogenetically, subsequently leading to aphid death. Some strains of P. syringae are known to deter aphids from feeding on plants based on the strain’s blue or green colored fluorescence. P. syringae produces a molecule, pyoverdine, that contributes to fluorescence of the bacterium, but not virulence to aphids. Aphid avoidance of these bacteria is positively correlated with bacterial virulence (e.g. more fluorescent strains are more avoided and more virulent), and we hypothesized that avoiding these pathogens may be an adaptive characteristic for aphids. However, this hasn’t been tested on a broad range of Pseudomonas strains. To assess these effects, we tested the virulence to aphids of diverse strains with varied ability to deter aphids. These assays were performed on pea aphids, Acyrthosiphon pisum, with the use of an artificial aphid diet for oral ingestion of bacteria. After a 24 hour exposure to bacteria, we measured aphid survival for 72 hours. Knowledge of bacterial virulence to aphids is useful for potential future uses in biocontrol of agricultural pests.