Gene silencing in adult Aedes aegypti mosquitoes through oral delivery of double-stranded RNA

Mosquitoes (Diptera: Culicidae) are the most medically important arthropods worldwide, vectoring numerous agents that negatively affect humans, including dengue, arboviral encephalitides and malaria parasites. These mosquito-borne pathogens adversely affect millions of people annually, and the total burden of diseases associated with mosquitoes is well documented (e.g. see Sachs and Malaney 2002; Hemingway et al. 2006; Suaya et al. 2009). Mosquito control relies heavily on the use of chemical insecticides, from aerial spraying to impregnated bed nets. However, because of increasing insecticide resistance induced by selection pressure, chemically based control of mosquito populations is becoming increasingly difficult. For example, a clear relationship has been demonstrated between the reduced efficacy of pyrethroid-impregnated bed nets and residual sprays to the increased frequencies of the kdr allele in Benin Anopheles gambiae populations (N’Guessan et al. 2007; Yadouleton et al. 2010). Resistance is not limited to Anophelines as surveillance programmes demonstrate a general trend in the rise of insecticide resistance in numerous mosquito species of medical importance (e.g. daCunha et al. 2005; Cui et al. 2006; Montella et al. 2007). Other negative impacts of insecticide usage include accumulation of the insecticide within the environment and the widespread killing of non-target organisms. Thus, insecticides can create a long-term burden on species diversity and ecosystem sustainability. Double-stranded RNA (dsRNA) is an attractive alternative as a potential bio-insecticide because it avoids the negative effects of chemical insecticides. Specifically, it poses no risk of accumulation within the environment because it is readily degraded by ubiquitous bacterial enzymes. In addition, it is highly sequence-specific and can be designed to avoid nontarget species toxicity. Within cells, dsRNA induces a cellular response called RNA interference (RNAi), a naturally occurring process by which transcriptional messages (mRNA) are silenced prior to translation by a large protein complex guided by complementary small interfering RNAs (siRNAs) that are generated