Résumé
The engineering and testing of genes that result in refractory phenotypes are important components of the continuing effort towards the use of population replacement strategies for vector control. Both ‘endogenous’ and ‘synthetic’ refractory phenotypes are being considered. Additional research is required to determine the prevalence of such phenotypes in the various vector–pathogen combinations, and the threshold levels of activity of genes conferring transmission blocking, as well as to develop efficient methods for the evaluation of their entire spectrum of biological effects.