Fig. 3.

Associations of rhizosphere bacteria with insect hosts might be diverse and range from mutualism to pathogenicity: Rhizosphere bacteria have multiple plant‐beneficial effects. They protect the plants against pathogens by competition, antagonism and induction of plant defences. However, they can also associate with plant‐interacting insects. Pseudomonas protegens CHA0 infects and kills lepidopteran insect larvae upon ingestion. Inside the insect body the bacteria multiply to very high numbers. From the cadaver the bacteria can recolonize plant roots. In nature, CHA0 might be rather an opportunistic pathogen, which often only persists inside insects without killing the host. In the case of the cabbage fly, CHA0 is able to persist transstadially and is dispersed by emerging adults to new host plants. Rhizosphere bacteria may move into aerial plant parts. Streptomyces globisporus colonizes strawberry flowers from where it is vectored by bees to new strawberry plants. It is yet unknown whether S. globisporus can move from the flower to the roots. Beewolves hunt honeybees and bury them in the soil. Thereby bee‐associated bacteria may get access to colonize plant roots. Moreover, beewolf wasps harbour Streptomyces pilanthi which they acquire from the environment. The streptomycete may be capable of colonizing plant roots as well. Stinkbugs harbour Burkholderia symbionts that provide a nutritional benefit to the insect. The bacteria are acquired from the environment and selected by a special symbiont sorting organ in the insect.