A Rickettsia endosymbiont influences whitefly (Bemisia tabaci) mortality by the fungal pathogen Beauveria bassiana.

Whiteflies belonging to the species complex known provisionally as Bemisia tabaci are costly global pests of agricultural and greenhouse crops, and important vectors of plant disease. Potentially contributing to their success, whiteflies in this complex have both nutritional bacterial endosymbionts and several facultative symbionts. The dominant B. tabaci in field crops in the USA, known as the “B” or “MEAM1”, is host to a symbiont, Rickettsia, which spread rapidly in the southwestern USA and confers fitness benefits to Rickettsia-infected whiteflies. We are exploring the relationship between the whitefly, their Rickettsia symbionts, and a natural entomopathogenic fungus Beauveria bassiana. We evaluated fungal pathogenesis in two whitefly genetic backgrounds, each with sublines of Rickettsia- positive and Rickettsia negative whiteflies. The data indicate whitefly mortality rates respond to the fungal concentration in a dose-dependent manner. Interestingly, Rickettsia infection reduces the proportion of whiteflies killed by fungus in one whitefly background, but has no protective effect on whiteflies in the second genetic background. Current efforts are focused on identifying possible reasons for the different effects of Rickettsia on susceptibility to fungal mortality in these two whitefly genetic backgrounds.