A perspective on the need and current status of efficient sex separation methods for mosquito genetic control

Abstract

Major efforts are currently underway to develop novel, complementary methods to combat mosquito-borne diseases. Mosquito genetic control strategies (GCSs) have become an increasingly important area of research on account of their species-specificity, track record in targeting agricultural insect pests, and their environmentally non-polluting nature. A number of programs targeting Aedes and Anopheles mosquitoes, vectors of human arboviruses and malaria respectively, are currently being developed or deployed in many parts of the world. Operationally implementing these technologies on a large scale however, beyond proof-of-concept pilot programs, is hampered by the absence of adequate sex separation methods. Sex separation eliminates females in the laboratory from male mosquitoes prior to release. Despite the need for sex separation for the control of mosquitoes, there have been limited efforts in recent years in developing systems that are fit-for-purpose. In this special issue of Parasites and Vectors we report on the progress of the global Coordinated Research Program on “Exploring genetic, molecular, mechanical and behavioural methods for sex separation in mosquitoes” that is led by the Insect Pest Control Subprogramme of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture with the specific aim of building efficient sex separation systems for mosquito species. In an effort to overcome current barriers we briefly highlight what we believe are the three main reasons why progress has been so slow in developing appropriate sex separation systems: the availability of methods that are not scalable, the difficulty of building the ideal genetic systems and, finally, the lack of research efforts in this area.

Sex Sorting for Pest Control: It’s Raining Men!

“…Culicinae mosquitoes (including the genera Aedes and Culex) exhibit size sexual dimorphism as pupae. Consequently, Aedes mosquitoes have been, and are still, mechanically separated based on pupal size [15]. In Italy, a SIT trial to control Ae.…”

“…polynesiensis iv,v . In Anopheles mosquitoes, the current sex separation method is based on manual pupal identification, which allows sex-sorting of only 500 pupae per hour (reviewed in [15]). The working time is therefore very high, and the number of mosquitoes necessary for a program is difficult to reach.…”

“…Abbreviations: L1, 1st instar larvae; L4, 4th instar larvae; WT, wild type; TR, transgenic; CM, obtained by classical mutagenesis; CT, chemically treated; NC, noncommunicated; Glossina, Glossina p. gambiensis and Glossina pallidipes. See also[15,19,26,[28][29][30]50,51,[53][54][55]59,60,62,64,69,70,72].…”

A generic white pupae sex selection phenotype for insect pest control

“…Extensive genetic and cytogenetic studies facilitated the development of a physical map of the medfly genome 8, . The annotated gene set provided opportunities for the identification of genes or loci-associated mutant phenotypes, such as the wp and tsl, used for the construction of GSS 16,17 . Salivary gland polytene chromosome maps developed for C. capitata, B. dorsalis, Z. cucurbitae, and B. tryoni show that their homologous chromosomes exhibit similar banding patterns.…”

Nixconfers heritable sex-conversion inAedes aegyptiandmyo-sexis needed for male flight

“…Coupling a Nix transgene with a conditional expression method (Fu et al, 2010), or a recently demonstrated gene drive strategy (Gantz et al, 2015;Kyrou et al, 2018) would enable the inheritance of the Nix transgene in almost all offspring, resulting in the removal or conversion of potentially all females. Such Nix transgenic lines that produce male-only progeny may be used as a population suppression method (Adelman and Tu, 2016) or to significantly reduce the cost and augment the scale of other mosquito control strategies that require the separation of males from females (Papathanos et al, 2018). The latest screening was done for G13 and G14 for N1 and N2 lines, respectively.…”