The major families are carboxyl esterases, glutathione s-transferase and the monooxygenases P450s. These enzymes can metabolize both endogenous compounds, which are produced by metabolism, and exogenous compounds present in environment, such as insecticides. Resistance to chemical insecticides as a consequence of increased metabolic capability of these enzymes is known as metabolic resistance, as the insecticide is metabolized or sequestered before reaching its target. In the last few years, many studies have demonstrated the molecular basis of metabolic resistance, and mechanisms such as co-amplification of genes, transposonmediated mutations, gene duplication and mutations in trans-regulatory elements have been reported. Li et al. have published a good review on this subject. One of the major threats to the control programmes of vector borne diseases is insecticide resistance, as most of the implemented strategies are based on the high throughput screening exclusive use of such compounds. Thus, managing resistance is fundamental to sustain these strategies. The design of molecular tools for screening alleles associated with target-site insensitivity in natural populations is feasible, because the molecules involved in this type of resistance are components of nervous system and thus are conserved across different taxa, allowing the detection of the same mutation in different species. On the other hand, as mentioned above, the nature of mutations in metabolic genes leading to resistance is diverse and, the development of molecular tools that could be used in a wide range of species to detect resistance alleles is a difficult task. Moreover, the amount of genes potentially involved in the metabolism of xenobiotics makes the task extremely challenging. The use of microarray analysis to measure and compare gene expression levels between resistant and susceptible mosquito strains has allowed the identification of genes that are involved in specific metabolic resistance mechanisms in Anopheles gambiae, Anopheles arabiensis and in Ae. aegypti. David et al. have constructed a microarray containing more than 200 detoxification gene specific for An. gambiae and have used this chip to investigate metabolic-based insecticide resistance. Similarly, Strode et al. developed the Ae. aegypti ‘Detox Chip’, which also contains more than 200 genes putatively involved with metabolic resistance. This Detox Chip has also been used to evaluate mosquito response to xenobiotic exposure. Almost half of the world’s population are believed to be at risk from Dengue and this is due in no small part to the fact that the vector Ae. aegypti is a mosquito which has superbly adapted to human activity and increasing urbanization. With no available vaccine, vector control is the only option in the fight against Dengue and insecticides are a vital weapon. Temephos is an organophosphate larvicide recommended by WHO to control Ae. aegypti larvae and is even sanctioned for use in potable water containers.