Assessments of fitness effects by the facultative symbiont Rickettsia in the sweetpotato whitefly (Hemiptera: Aleyrodidae)

The sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), harbors several bacterial symbionts, including the obligate primary symbiont Portiera aleyrodidarum and the facultative secondary symbionts Arsenophonus, Cardinium, Fritschea, Hamiltonella, Rickettsia, and Wolbachia. The roles of these symbionts are yet unknown. In this study, we tested for possible effects of one symbiont, Rickettsia, on some fitness parameters of B. tabaci (biotype B) by comparing whiteflies that carry this symbiont to whiteflies that do not. Preadult development of Rickettsiacarrying whiteflies was faster, but all the other parameters that were measured: longevity, total number of progeny, sex ratio, and nymphal survivorship did not differ significantly. Estimates of the intrinsic growth rate (r) were almost identical for the two groups. Cross-mating between Rickettsia-canying and Rickettsia-free whiteflies provided no evidence for cytoplasmic incompatibility. Vertical transmission of Rickettsia was found to be nearly complete. Our results do not clearly identify a selective advantage that would explain the high prevalence of Rickettsia in B. tabaci populations, thus, other fitness parameters and horizontal transmission routes are suggested and discussed.