Insecticides have been used intensively to control insect populations over the last 50 years and many species of insects have developed resistance to several families of insecticides, These resistances are mainly due to two mechanisms: mutation of the insecticide target protein (leading to a decrease in its affinity for the concerned insecticide family), and increased detoxification, Recent molecular studies suggest that the mutations conferring resistance are rare and sometimes unique events in any given species, The wide geographic distribution of some of these genes can then only be explained by the balance between migration and selection at the population level.