Seite - 79 - in Biodiversity and Health in the Face of Climate Change

79 temperature, the Relative Control Potential metric has been developed to allow the right selection of a living biological control agent for specific temperature condi- tions (Cuthbert et  al. 2018). 4.4.3 New Genetic Tools in  Vector Control Recent advances to modernise and develop new vector control and surveillance tools mean that there has never been a better time to reinvigorate vector control. The genetic control of vectors will add to the existing vector control toolbox. Certain genetic vector control strategies have a greater advantage as they will perform even better when climatic conditions favour vector population growth and development. Furthermore, genetic vector control targets only one species and thereby could avoid direct negative effects on non-target species. The sterile insect technique (SIT) is based on the release of sterile mosquito males, produced by irradiation or sterilising chemicals, mating with wild females and thereby suppressing the mosquito population growth. However, the successful implementation of SIT requires a repeated release of a high number of mosquitoes with ideally no fitness costs if compared to wild counterparts. Therefore mass- rearing facilities have been set up and several sex-sorting techniques for pupae have been developed. SIT successfully eliminates or suppresses populations, as shown for Cx. quinquefasciatus on an island in Florida and Anopheles albimanus in El Salvador or Ae. albopictus in Italy (reviewed in Baldacchino et  al. 2015). Alternatively, insects can be sterilised or immunised by genetic modifications (GMs), which is a more precise procedure and goes along with less fitness costs for male mosquitoes. The release of transgenic sterile male mosquitoes carrying a dom- inant lethal genetic system (RIDL technique) has been successfully applied for dengue-carrying mosquitoes in the Caribbean (Harris et  al. 2011), Malaysia (Lacroix et  al. 2012) and Brazil (Carvalho et  al. 2015). However, as with SIT, repeated releases with large numbers of males are necessary to efficiently control insect vec- tors and agricultural pest insects. The release of gene-drive insects for population suppression or vector immuni- sation might be an even more promising technique. Preliminary studies have con- firmed the feasibility of using gene drive-based modifications for vector control (Hammond et  al. 2016; Burt et  al. 2018). Gene-drives rely on an endonuclease cassette (e.g. CRISPR-Cas9) targeting genes important for fitness of the vector or inhibit parasite development. This endonuclease cassette spreads through the tar- get population by modifying/cutting the DNA of target genes in the germline of every offspring. When the DNA in wild-type insects is repaired, the DNA of genetically modified insects serves as the DNA template. As a result, the endo- nuclease cassette copies to the wild-type DNA.  This way, the gene-drive construct passes via germline modification to almost every offspring and from generation to generation. This hypothetical self-sustaining behaviour of gene-drives might be a clear advantage, because the reduction of release efforts is necessary to save costs, 4 Vector-Borne Diseases