New self-sexing Aedes aegypti strain eliminates barriers to scalable and sustainable vector control for governments and communities in dengue-prone environments.

For more than 60 years, efforts to develop mating-based mosquito control technologies have largely failed to produce solutions that are both effective and scalable, keeping them out of reach of most governments and communities in disease-impacted regions globally. High pest suppression levels in trials have yet to fully translate into broad and effective Aedes aegypti control solutions. Two primary challenges to date-the need for complex sex-sorting to prevent female releases, and cumbersome processes for rearing and releasing male adult mosquitoes-present significant barriers for existing methods. As the host range of Aedes aegypti continues to advance into new geographies due to increasing globalisation and climate change, traditional chemical-based approaches are under mounting pressure from both more stringent regulatory processes and the ongoing development of insecticide resistance. It is no exaggeration to state that new tools, which are equal parts effective and scalable, are needed now more than ever. This paper describes the development and field evaluation of a new self-sexing strain of Aedes aegypti that has been designed to combine targeted vector suppression, operational simplicity, and cost-effectiveness for use in disease-prone regions. This conditional, self-limiting trait uses the sex-determination gene doublesex linked to the tetracycline-off genetic switch to cause complete female lethality in early larval development. With no female progeny survival, sex sorting is no longer required, eliminating the need for large-scale mosquito production facilities or physical sex-separation. In deployment operations, this translates to the ability to generate multiple generations of suppression for each mosquito released, while being entirely self-limiting. To evaluate these potential benefits, a field trial was carried out in densely-populated urban, dengue-prone neighbourhoods in Brazil, wherein the strain was able to suppress wild mosquito populations by up to 96%, demonstrating the utility of this self-sexing approach for biological vector control. In doing so, it has shown that such strains offer the critical components necessary to make these tools highly accessible, and thus they harbour the potential to transition mating-based approaches to effective and sustainable vector control tools that are within reach of governments and at-risk communities who may have only limited resources.

Genome scan in the mosquito Aedes rusticus: population structure and detection of positive selection after insecticide treatment.

Identification of genes involved in local adaptation is particularly challenging for species functioning as a network of interconnected populations undergoing frequent extinctions-recolonizations, because populations are submitted to contrasted evolutionary pressures. Using amplified fragment length polymorphism markers, population genetic structure of the mosquito Aedes rusticus was analysed in five geographical areas of the French Rhône-Alpes region. We included a number of sites that were treated with the bio-insecticide Bacillus thuringiensis israelensis (Bti) for more than 15 years. Analysis of molecular variance revealed that most of the genetic variability was found within populations (96%), with no significant variation among geographical areas, although variation among populations within areas (4%) was significant. The global genetic differentiation index F(ST) was low (0.0366 +/- 0.167). However, pairwise F(ST) values were significant and no isolation-by-distance at the regional level was observed, suggesting a metapopulation structure in this species. Bti-treatment had no effect on genetic structure and on within-population genetic diversity. Potential signatures of positive selection associated with Bti-treatment were detected for five loci, even though toxicological bioassays performed on field-collected larvae showed no significant difference in mortality between Bti-treated and nontreated sites. The difficulty of detecting moderate resistance in field-collected larvae together with possible differential persistence of toxins in the environment may explain our inability to detect a toxicological response to Bti in treated sites. The evidence for positive selection occurring at several genomic regions suggests a first step towards Bti resistance in natural mosquito populations treated with this bio-insecticide. Furthermore, this signal was detectable using genomic tools before any toxicological evidence for resistance could be identified.

Genetic differentiation of populations within the Culex pipiens complex and phylogeny of related species.

The Culex pipiens complex consists of several species, subspecies, forms, races, physiological variants, or biotypes according to different authors and includes the 2 holarctic variants Cx. pipiens biotype pipiens and Cx. pipiens biotype molestus. Differences in morphological characters are overlapping and thus are delimited in their taxonomic value, even when behavioral and reproductive specializations are apparent. Our enzyme electrophoretic study included 7 geographic populations of Cx. pipiens biotype pipiens and 7 of the biotype molestus from several European countries. For comparison, 5 populations of Culex quinquefasciatus from Asia, Africa, and North America were examined. The aim was an assessment of the extent of genetic differences between local populations of the biotypes pipiens and molestus versus the degree of differentiation between geographic populations of both groups. Culex torrentium, Cx. modestus, Culex stigmatosoma, and Culex territans were studied for comparison as taxonomical well-defined species. The population genetic analyses revealed much higher genetic distances between local populations of Cx. pipiens biotype pipiens and Cx. pipiens biotype molestus compared to the low differentiation between geographic populations within each taxon. The UPGMA analysis and F-statistics position the geographic populations in discrete monophyletic clusters. Gene flow between local populations of the biotypes pipiens and molestus could be shown to be lower than gene flow between geographically distant populations within each of the 2 groups, leading to the conclusion that Cx. pipiens biotype molestus could be a distinct taxon. Culex quinquefasciatus could be diagnosed as genetically well separated, in particular by the diagnostic enzyme marker MDH (NADP). Two genetic enzyme markers were identified to differentiate Cx. torrentium from Cx. pipiens s.l. Culex modestus, Cx. stigmatosoma, and Cx. territans showed considerable genetic distances to the species of the Culex pipiens complex and between each other, and several genetic markers could be identified.