Repressed Beauveria bassiana infections in Delia antiqua due to associated microbiota

ABSTRACT BACKGROUND Insects form both mutualistic and antagonistic relationships with microbes, and some antagonistic microbes have been used as biocontrol agents (BCAs) in pest management. Contextually, BCAs may be inhibited by beneficial insect symbionts, which can become potential barriers to entomopathogen‐dependent pest biocontrol. Using the symbioses formed by one devastating dipteran pest, Delia antiqua , and its associated microbes as a model system, we sought to determine whether the antagonistic interaction between BCAs and microbial symbionts could affect the outcome of entomopathogen‐dependent pest biocontrol. RESULTS The result showed that in contrast to non‐axenic D. antiqua larvae, i.e., onion maggots, axenic larvae lost resistance to the entomopathogenic Beauveria bassiana , and the re‐inoculation of microbiota increased the resistance of axenic larvae to B. bassiana . Furthermore, bacteria frequently isolated from larvae, including Citrobacter freundii , Enterobacter ludwigii , Pseudomonas protegens , Serratia plymuthica , Sphingobacterium faecium and Stenotrophomonas maltophilia , suppressed B. bassiana conidia germination and hyphal growth, and the re‐inoculation of specific individual bacteria enhanced the resistance of axenic larvae to B. bassiana . CONCLUSION Bacteria associated with larvae, including C. freundii , E. ludwigii , P. protegens , S. plymuthica , S. faecium and S. maltophilia , can inhibit B. bassiana infection. Removing the microbiota can suppress larval resistance to fungal infection. © 2018 Society of Chemical Industry