Abstract
The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) harbors several bacterial symbionts. Among the secondary (facultative) symbionts, Hamiltonella has high prevalence and high infection frequencies, suggesting that it may be important for the biology and ecology of its hosts. Previous reports indicated that Hamiltonella increases whitefly fitness and, based on the complete sequencing of its genome, may have the ability to synthesize cofactors and amino acids that are required by its host but that are not sufficiently synthesized by the host or by the primary endosymbiont, Portiera. Here, we assessed the effects of Hamiltonella infection on the growth of B. tabaci reared on low-, standard-, or high-nitrogen diets. When B. tabaci was reared on a standard-nitrogen diet, no cost or benefit was associated with Hamiltonella infection. But, if we reared whiteflies on low-nitrogen diets, Hamiltonella-infected whiteflies often grew better than uninfected whiteflies. Furthermore, nitrogen levels in field-collected whiteflies indicated that the nutritional conditions in the field were comparable to the low-nitrogen diet in our laboratory experiment. These data suggest that Hamiltonella may play a previously unrecognized role as a nutritional mutualist in B. tabaci.
Highlights
Many insect species harbor intracellular, bacterial symbionts, and the interaction between bacterium and insect can be parasitic, mutualistic, or neutral [1]
When B. tabaci females were reared on the standard diet, the relative growth rate (RGR) showed no significant difference between Hamiltonella-infected and noninfected whiteflies in any trials of the three experiments (Fig. 1–3)
When B. tabaci females were reared on diets that contained high levels of nitrogen, Hamiltonella-infected whiteflies showed 45% higher RGR than did noninfected whiteflies in trial 1, but it showed no differences in trial 2 and 3 (Fig. 1)
Summary
Many insect species harbor intracellular, bacterial symbionts, and the interaction between bacterium and insect can be parasitic, mutualistic, or neutral [1]. These symbiotic bacteria, which are strictly maternally inherited, can affect insect defense against natural enemies and pathogens [2,3,4,5,6], dispersal behavior [7], pest status [8], thermal resistance [9,10], virus vector competence [11,12], reproduction (including sex ratio) [13], and body color [14]. The latter study demonstrates that a symbiont’s contribution may only be apparent when the host is nutritionally compromised
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