Influence of secondary symbionts on host plant utilization and selection in the tobacco whitefly, Bemisia tabaci ; Influence des symbiotes secondaires sur l’utilisation et la sélection de la plante hôte chez l’aleurode du tabac, Bemisia tabaci

Microbial symbionts are universal in eukaryotes, and it is now recognized that symbiotic associations represent a major source of biological and evolutionary innovation. However, the extent to which symbionts contribute to their hosts' ecological adaptation and subsequent diversification is far from being fully elucidated. The tobacco whitefly Bemisia tabaci is a highly diversified cryptic species complex. All members of this species complex are associated with an obligate, so-called ‘primary’ symbiont, Portiera aleyrodidarum, which is essential to its host survival. Portiera provides B. tabaci with nutrients (amino acids, vitamins) that are essential for its development and growth, nevertheless limiting in its diet, the plant phloem sap. As in many phloemophageous insects, most B. tabaci individuals also host one or more facultative ‘secondary’ symbionts whose roles remain poorly known. In this projet, we investigated whether and how secondary symbionts influence host plant utilization and selection by B. tabaci, using three lines differing in their secondary symbiont community. To better apprehend the interactions between B. tabaci, its symbionts and plants, we first analyzed the life history traits and physiology of these three lines when reared on three host plants with significantly different nutritional properties (amino acid content): hibiscus, tobacco and lantana. We showed that insect performance, free amino acid and symbiont density depend on the host plant species, suggesting a critical role for the plant nutritional properties. Insects reared on lantana showed a different free amino acid profile than insects reared on the other plants, higher symbiont density, and reduced fecundity. Together, these results indicate that lantana is the least favorable plant for B. tabaci of the three plants tested. These results allowed us to establish a framework in which we investigated the relative contributions of the insect nuclear genotype and cytotype (corresponding to the cytoplasmic compartment of an ...