Exploring Genetic, Molecular, Mechanical and Behavioural Methods of Sex Separation in Mosquitoes

Among the major vectors of human diseases, mosquitoes are the most devastating ones. In addition, urbanization, globalization and climate change have further accelerated the spread and outbreaks of new mosquito borne diseases. In view of the problems associated with conventional mosquito control, such as resistance and health effects, major efforts are required to develop new or complementary control techniques, including the SIT, for major mosquito species.

The Sterile Insect Technique (SIT) is an increasingly important component of area-wide integrated vector control (AW-IVC) programmes for key insect vectors such as mosquitoes. With the increase in vector-borne diseases and their toll on human health and mortality, there have been recurring requests from Member States to develop tools and techniques for mosquito SIT, including the development of sexing strains (GC(56)/RES/19) to be able to apply the SIT to control mosquito vector populations (Resolution GC(52)/RES/13). The SIT has the ability to suppress or in special situations to eradicate existing vector populations and to prevent the establishment of new outbreaks.

Operational use of the SIT in other insect pests continues to reveal areas where new technologies could further improve efficiency and thus lead to more efficacious programmes. There are many aspects of the mosquito SIT package that require increased efficiency to be able to reach the operational level, e.g. improved mass rearing, release technology, quality control, field monitoring, etc. However, one critical area where important advances need to be made before any SIT application is possible concerns the development of genetic sexing strains (GSS). Unlike agriculture pests where the releases of both sexes is primarily of economic concern, in mosquitoes, it is an essential prerequisite to release only males since females are blood feeders and transmit the diseases. Without male-only releases, SIT application against mosquitoes is not possible.

Currently, AW integrated pest management (IPM) programmes with an SIT component have been successfully implemented for several very important fruit fly and lepidopteran species where the development of improved strains, especially GSS (in the case of fruit flies), led to major increases in applicability and efficiency of the SIT component. The experience gained from these programmes would prime the new CRP for the development of GSS in mosquitoes.

There are several mosquito species that are vectors of different pathogens in different countries. Of these, based on the severity of the disease, requests from Member States and the availability of the scientific tools and information, the consultants recommend that the initial efforts to develop mosquito GSS should focus on the following species: Anopheles arabiensis (vector of malaria), Aedes albopictus and Ae. aegypti (vectors of dengue, chikungunyia etc.). If research proposals on some of the other species of significant interest are received, they should also be considered. Mosquito GSS development can be achieved using different approaches, but they all rely on some form of stable genetic change introduced and maintained in the developed strain. Genetic change can be introduced either using irradiation and classical genetics (as in the case of Mediterranean fruit fly GSS) or modern biotechnology, specifically genetic transformation. Both approaches have advantages and disadvantages relating to transferability of systems between species, stability in mass-rearing, regulatory approval, etc. In addition, the existing alternative sex separation methods based on physical, mechanical and behavioural approaches should also be considered. However, it should be noted that these alternative methods are currently appropriate only for small scale operations, highlighting the need to develop for large scale SIT and non-SIT operations state of art sexing strategies based on genetic, molecular and mechanical approaches.

Three main research axes to be addressed by the CRP:

  • Explore irradiation and classical genetic approaches for sex separation in mosquitoes - development of GSS based on irradiation and classical genetics
  • Explore molecular approaches for sex separation in mosquitoes - Development of GSS based on molecular genetics
  • Explore mechanical, behavioural and developmental approaches for sex separation in mosquitoes - Sex Separation using Mechanical, Behavioural, and Developmental Tools.

A combination of the following priority topics will be targeted:

  • [1] Isolation and mapping of genetic markers from different sources including natural populations and / or EMS-based screens
  • [2] Development and characterization of irradiation-induced chromosomal rearrangements in the target mosquito species
  • Cytogenetic analysis of the tools developed in [1] and [2]
  • Isolation and characterization of selectable markers
  • Construction and characterization of GSS
  • Evaluation of GSS on a small scale using standard quality control parameters
  • Unravelling the molecular mechanisms of sex determination and sex specific expression in mosquitoes
  • Isolation of genes and promoters to build transgenic strains
  • Application of techniques to obtain sex specific expression of lethal factors in several species
  • Construction of transgenic sexing strains in mosquitoes
  • Evaluation of transgenic strains at a small scale using standard quality control parameters
  • Construction of transgenes with site-specific landing sites
  • Evaluation and distribution of landing site strains
  • Develop new and improve existing mechanical, behavioural tools for sex separation.

Participants:

Thirteen participants: Brazil, Cameroon, Cuba, France, French Polynesia, Germany, Italy, Pakistan, South Africa, Spain, Sri Lanka, United Kingdom, United States of America.

Reports:


Project Officer:

Kostas Bourtzis and Jeremy Bouyer