Te2 has been show to be involved in the dehydrochlorination of DDT in both Ae. aegypti and An. gambiae and partial silencing of GSTe2 in Ae. aegypti leads to a reduction of resistance in the mosquito. What we don’t know at this stage is whether the over expressed genes observed in this study are similarly effective against temephos. This issue is currently being addressed at LSTM alongside the profiling of CYP6N12 enzymatic activity against a range of insecticides. One of the presumptions of resistance management, is that by ceasing the selection pressure on an insect population, the resistant PI-103 phenotype will most probably revert to susceptible. This strategy is based on evidence which suggests resistance is associated with fitness costs. For example, pyriproxyfen resistance in Bemisia tabaci resulted in a reduction of 25% in life characteristics such as nymph survival, sex ratio, fecundity, egg hatching rate and development time. Halting a spraying campaign once resistance has been detected or alternating the use of different classes of insecticides are recommended tactics to control the spread of insecticide resistance. Few studies have investigated the reversal of resistance and none have demonstrated a decrease in the expression of genes implicated in conferring resistance. One of the most interesting findings of the current study was that a decrease in temephos resistance was followed by decreases in expression levels of the previously significantly over expressed genes and a reduction in metabolic enzyme activities. When temephos exposure was terminated at F13, there was an increase in temephos susceptibility in RecRev1 after 13 generations. With the exception of GSTi1, all of the analyzed RecR over expressed genes presented lower expression in the RecRev1 population. The most significant decline was observed with CYP6N12, which dropped from,7.5 fold to,1 fold. This finding reinforces the assumption that these genes are directly involved in conferring temephos resistance in this strain. The speed with which over expression of metabolic enzymes become fixed in a population is not clear and one intriguing question is whether metabolic genes are induced following insecticide application or whether they are constitutively expressed. In order to determine whether a single exposure to temephos induced gene expression, the RecRev1 population was subjected to insecticide exposure. Across the six genes analysed, there was no significant over expression upon temephos exposure in RecRev1 individuals. In fact, Aldehyde oxidase 10382 and GSTo1 demonstrated a,50% reduction in fold change expression. The reason for such a dramatic reduction in the expression of these two genes is unclear. Induction of gene expression has been observed in susceptible strains of Ae. aegypti after exposure of sub-lethal doses of insecticides or xenobiotics. Although the constitutive expression of genes that encode for detoxifying enzymes may appear more costly than inducing them following exposure, it ensures that the mosquito is always primed for an insecticide “attack”.