Toxicity (a,b) and comparative effects of synergists (c,d) on mortality caused by permethrin and deltamethrin to larvae (L4) of two Brazilian strains of Aedes aegypti. (a,b) The lines denote the lethal concentration (LC) values estimated based on concentration-mortality bioassays using probit analyses. Symbols show the averaged mortality for each insecticide concentration applied to each population of A. aegypti. The vertical bars represent the standard error of the average (SE). (c,d) The effects of the synergists piperonyl butoxide (PBO), diethyl maleate (DEM) and triphenyl phosphate (TPP) on the mortality of the resistant population caused by pyrethroids at the LC50 obtained for the resistant strain. Asterisks indicate significant differences in relation to the unsynergized insecticide (one-way ANOVA with Scheffe’s post hoc analysis, P < 0.05).