Mosquito-borne diseases such as malaria or dengue fever cause a huge health burden to people living in tropical and subtropical countries. Current control efforts are not always effective and many of these diseases have increased in prevalence, geographic distribution and severity. The transinfection of Aedes aegypti mosquitoes with the endosymbiotic bacterium Wolbachia pipientis is a promising biocontrol approach for those diseases. Naturally occurring Wolbachia strains have been stably introduced from fruit flies into mosquitoes and shown that these strains can invade and sustain themselves in mosquito populations while blocking the replication of dengue viruses and other pathogens inside the insects. This chapter discusses the release of Wolbachia-infected A. aegypti mosquitoes in North Queensland, Australia. The regulatory process for this kind of release had no precedent in Australia and was authorised after a thorough community engagement process and an independent risk assessment. At the time of writing (April 2012), a second release trial was currently underway in Queensland and the technology will soon be deployed in dengue-endemic areas of Southeast Asia and in Brazil, once appropriate approvals are in place.

Insecticides that kill the mosquito and drugs that kill the parasite are the only weapons presently available to fight the unbearably high human malaria toll. As mosquito and parasite resistance to these agents limits their effectiveness and there is currently no effective malaria vaccine available, clearly new means to fight the disease must be developed. This chapter explores the feasibility of an alternative strategy: rather than kill the vector mosquito, modify it to render it incapable of sustaining parasite development. This chapter investigates genetically modifying the symbiotic bacteria that naturally occur in the mosquito’s midgut, by producing bacteria that carry the same anti-parasite genes. Major remaining challenges are to devise means to introduce the modified bacteria into mosquitoes in the field and to resolve regulatory and ethical issues related to the release of genetically modified organisms in nature.