Behavioral Responses of Mosquitoes to Insecticides

Many people living in areas of the tropical and subtropical world are at serious risk of infection from a wide variety of vector-borne diseases, most notably malaria and dengue. Globally, approximately 50-100 million people are estimated to be at risk of infection with dengue viruses (the cause of dengue fever/dengue haemorrhagic fever) and between 100300 million live in malaria endemic areas (World Health Organization [WHO], 2009). The viruses responsible for dengue are transmitted primarily by Aedes aegypti, a predominately urban, day-biting mosquito that often resides in and around human dwellings and preferentially feeds on humans (Gubler, 1997); whereas the 4 human malaria parasites (Plasmodium) are transmitted by a wide variety of Anopheles species (Service & Townson, 2002 ). Dengue vector has proven extremely resilient to control measures because of its close association and exploitation of domestic and peridomestic human settings (Reiter & Gubler, 1997). On the other hand, malaria vectors display a more diverse array of host seeking behaviors and preference, biting patterns and larval breeding habitats (Pates & Curtis, 2005; Sinka et al., 2011). Despite decades of extensive research, efficacious and commercially viable vaccines for these 2 important vector-borne diseases are not yet available. Therefore, the prevention and control of dengue and malaria remains dependent on various vector control strategies to reduce risk of transmission; in some instances this requires the use of various chemical insecticides as larvicides, space spray and indoor residual spray (IRS) applications, and use of insecticide-impregnated bed nets to control adult mosquito blood feeding (Roberts & Andre, 1994; WHO, 1999; Reiter & Gubler, 1997; Grieco et al., 2007). Chemical insecticides, including organochlorines, organophosphates, carbamates, and synthetic pyrethroids, have long been used with great effect in public health vector control programs worldwide (Reiter & Gubler, 1997; Roberts & Andre, 1994; WHO, 1992). Although DDT used ceased in many countries several decades ago, the chemical has returned for use in malaria control IRS programs in Africa because of some its superior attributes (Roberts & Tren, 2010). The dramatic impact of DDT on mosquito populations in terms of both toxicity and behavior suppressing disease transmission is well known but in some instances the actual mechanisms at work remain unclear and poorly understood. Most studies on insecticides have placed attention exclusively on the direct toxicological (knockdown and killing) effects on mosquito populations; whereas far less research has focused on the