Fig. 1.

Pseudomonas protegens has a multi‐host lifestyle in plants and insects and can be vectored to new plants by the cabbage root fly Delia radicum. 1. The rhizosphere is colonized by P. protegens, which protects the plant against pathogenic fungi. 2. Insect larvae that feed on the roots of the plant ingest P. protegens cells. 3. Pseudomonas protegens persists in larvae of the cabbage root fly (D. radicum) and other insect larvae. 4. Pseudomonas protegens persists in D. radicum pupae. 5. The pupae develop into deformed adults or 6. into healthy flies. 7. Healthy D. radicum flies lay their eggs at the base of the plant on the soil and can transfer P. protegens cells to the rhizosphere. 8. When P. protegens kills the insect host, it mass replicates inside the larvae. 9. Pseudomonas protegens cells escape from the dead larvae, and migrate into the soil, from where they colonize the rhizosphere. Inlay: Diagram that indicates the nature of the interactions of the bacteria with the insect, the plant and soilborne plant pathogens. Green arrow, beneficial; orange arrow, neutral; red inhibition arrow, negative interaction. The figure has been adapted from Flury et al., ²⁰¹⁹ .