Biochemical monitoring of organophosphorus and carbamate insecticide resistance in Aedes aegypti mosquitoes from Trinidad

The urban mosquitoAedes aegypti (L.) (Diptera: Culicidae) transmits dengue and yellow fever in many tropical countries. In Caribbean islands, Ae. aegyptiposes an increasing public health threat where dengue types 1, 2 and 4 are endemic (Nathan & Knudsen, 1991). Aedes aegypti control is undertaken through community participation in the elimination of watercontainer breeding-sites, with variable success. Organophosphorus insecticides (OPs) have also been used against Ae. aegyptiduring the last 15–20 years (Georghiou et al., 1987). In Trinidad, temephos 1% sand granules are routinely applied for larval control in water storage containers, while malathion is used as an adulticide by ultra low volume spraying during periods of high prevalence of mosquitoes and/or dengue. Resistance to a range of OPs has been detected at low levels in Trinidad populations of Ae. aegypti , affecting both the larval and adult life stages (Rawlins & Wan, 1995). OP resistance in strains of Culex mosquitoes is commonly mediated by two different mechanisms: (1) elevated esterase activity, due to the gene amplification and/or increased transcription (Raymond et al., 1989; Vaughan & Hemingway, 1995) and subsequent over-expression of nonspecific esterases (Prabhaker et al., 1987; Takahashi & Yasutomi, 1987; Hemingway et al., 1990; Wirth et al., 1990) which sequester the OP before it reaches its target site, acetylcholinesterase (AChE). (2) Insecticide-insensitive AChE (iAChE) (Kamimura & Maruyama, 1983; Raymond et al., 1985; Villani & Hemingway, 1987). It has been suggested that elevated esterase activity may also be associated with insecticide resistance inAe. aegypti(Mourya et al., 1993). However, to date, neither elevated esterase activity nor iAChE have actually been identified as insecticide resistance mechanisms in Ae. aegypti . In Culex mosquitoes, the