Isobolograms of insecticidal activity for propoxur, DEET and their mixtures on Ae. aegypti. In absence of synergist (A), with PBO (B) and with DEF (C). Diagonal lines connect doses of equipotent activity for each product applied alone. Relative symbols indicate the amount of each product required to induce the same effect in a mixture (at the ratio based on median-effect doses of each product). Points below relative line indicate synergism, points close to relative line indicate additive effect, and points above relative line indicate antagonism between the compounds.