Costs of resistance in an insecticide-free environment. The number of female mosquitoes emerging in an insecticide-free environment. Insecticide susceptible strain SLAB is shown in an open column and the three resistant strains are shown in hatched columns. In two replicate experiments, there were nine or ten pots initially containing 100 larvae for each of the four strains. Different letters above columns indicate significant differences (p < 0.05) in female emergence as found by a Tukey-Kramer test (see text for details).