The Facultative Symbiont Rickettsia Protects an Invasive Whitefly against Entomopathogenic Pseudomonas syringae Strains
ABSTRACTFacultative endosymbionts can benefit insect hosts in a variety of ways, including context-dependent roles, such as providing defense against pathogens. The role of some symbionts in defense may be overlooked, however, when pathogen infection is transient, sporadic, or asymptomatic. The facultative endosymbiontRickettsiaincreases the fitness of the sweet potato whitefly (Bemisia tabaci) in some populations through mechanisms that are not yet understood. In this study, we investigated the role ofRickettsiain mediating the interaction between the sweet potato whitefly andPseudomonas syringae, a common environmental bacterium, some strains of which are pathogenic to aphids. Our results show thatP. syringaemultiplies within whiteflies, leading to host death, and that whiteflies infected withRickettsiashow a decreased rate of death due toP. syringae. Experiments using plants coated withP. syringaeconfirmed that whiteflies can acquire the bacteria at a low rate while feeding, leading to increased mortality, particularly when the whiteflies are not infected withRickettsia. These results suggest thatP. syringaemay affect whitefly populations in nature and thatRickettsiacan ameliorate this effect. This study highlights the possible importance of interactions among opportunistic environmental pathogens and endosymbionts of insects.