Insect population dynamics under Wolbachia -induced cytoplasmic incompatibility: puzzle more than buzz in Drosophila suzukii

Abstract Wolbachia pipientis is an intracellular bacterium that infects many insects and other arthropods. Cytoplasmic incompatibility (CI) is one of several effects that Wolbachia has on its hosts. In its simplest form, CI causes host reproductive failure when an uninfected female mates with an infected male. Theoretically, this has two consequences. First, when an incompatible Wolbachia strain is introduced into a recipient host population, uninfected females are selected against, triggering Wolbachia invasion. Second, reproductive failures during Wolbachia invasion lead to a transient decrease in population growth rate. Modelling studies combining Wolbachia invasion and host population dynamics show that these two processes could interact to cause population decline and even extinction. However, these effects could be sensitive to density dependence, with competition reducing the demographic impact of CI and Allee effect increasing the probability of extinction. We tested these predictions with laboratory experiments in the fruit fly Drosophila suzukii and the exogenous Wolbachia strain w Tei. Surprisingly, the introduction of w Tei into D. suzukii populations at carrying capacity did not result in the expected invasion of w Tei and transient population decline. In parallel, we found strong negative density dependence, but no Allee effect. From these results, we propose that negative density dependence is an important but underappreciated driver of the eco-evolutionary feedback underlying Wolbachia invasion and insect population dynamics. If future models and data support this hypothesis, pest management strategies using Wolbachia -induced CI should target early-season populations with negligible competition but a possible Allee effect

Analyses of symbiotic bacterial communities in the plant pest Bemisia tabaci reveal high prevalence of Candidatus Hemipteriphilus asiaticus on the African continent

International audienceMicrobial symbionts are widespread in insects and some of them have been associated to adaptive changes. Primary symbionts (P-symbionts) have a nutritional role that allows their hosts to feed on unbalanced diets (plant sap, wood, blood). Most of them have undergone genome reduction, but their genomes still retain genes involved in pathways that are necessary to synthesize the nutrients that their hosts need. However, in some P-symbionts, essential pathways are incomplete and secondary symbionts (S-symbionts) are required to complete parts of their degenerated functions. The P-symbiont of the phloem sap-feeder Bemisia tabaci, Candidatus Portiera aleyrodidarium, lacks genes involved in the synthesis of vitamins, cofactors, and also of some essential amino-acids. Seven S-symbionts have been detected in the B. tabaci species complex. Phenotypic and genomic analyses have revealed various effects, from reproductive manipulation to fitness benefits, notably some of them have complementary metabolic capabilities to Candidatus Portiera aleyrodidarium, suggesting that their presence may be obligatory. In order to get the full picture of the symbiotic community of this pest, we investigated, through metabarcoding approaches, the symbiont content of individuals from Burkina Faso, a West African country where B. tabaci induces severe crop damage. While no new putative B. tabaci S-symbiont was identified, Candidatus Hemipteriphilus asiaticus, a symbiont only described in B. tabaci populations from Asia, was detected for the first time on this continent. Phylogenetic analyses however reveal that it is a different strain than the reference found in Asia. Specific diagnostic PCRs showed a high prevalence of these S-symbionts and especially of Candidatus Hemipteriphilus asiaticus in different genetic groups. These results suggest that Candidatus Hemipteriphilus asiaticus may affect the biology of B. tabaci and provide fitness advantage in some B. tabaci populations

Influence of secondary symbionts on host plant utilization and selection in the whitefly Bemisia tabaci.

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Study of host-symbionts coevolution in the whitefly Bemisia tabaci: an experimental evolution approach

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