AimsWe aim to determine if Pseudomonas fluorescens is a viable biological control for Erwinia tracheiphila within the insect vector, Acalymma vittatum. Methods and ResultsPseudomonas fluorescens secreted fluorescein and inhibited growth of E. tracheiphila in disc diffusion assays. To determine if this antagonism was conserved within the insect vector, we performed invivo assays by orally injecting beetles with bacterial treatments and fluorescent insitu hybridization to determine bacterial presence within the alimentary canal. ConclusionsPseudomonas fluorescens inhibited the growth of E. tracheiphila on a nutrient-limiting medium. In situ experiments demonstrated that P. fluorescens is maintained within the alimentary canal of the beetle for at least 4days, and co-occurred with E. tracheiphila. When beetles were first presented with Pseudomonas and then challenged with E. tracheiphila, E. tracheiphila was not recovered via FISH after 4days. These data suggest that P. fluorescens has potential as a biological control agent to limit E. tracheiphila within the insect vector. Significance and Impact of the StudyThis is a novel approach for controlling E. tracheiphila that has the potential to decrease reliance on insecticides, providing a safer environment for pollinators and growers.