Different colors of mosquitoes in this picture represent a single base pair change, which is one of the mechanisms that can cause variability in a population, that can cause the different genes to insecticide resistance that the individual might have. Linda’s lab at the CDC is studying this genetic diversity. For example, adults that have been found to be resistant (they test them by exposing them to standard amounts of insecticides) could have the kdr mutation, as well as multiple copies of two esterase genes. They extract that individual’s DNA and are interested in the differences in the DNA sequences of both known resistance genes such as kdr and esterases, as well as several other genes. They compare the genetic variation of resistant individuals to individuals that are susceptible to the insecticide. This co-variation in a set of genes in resistant vs. susceptible mosquitoes can give them a better picture of what genes are involved in resistance.