The Lahore area of Pakistan has been malathion spraying pressure since 1976 at the rate of two treatments per year, 1 gm/m2 per round. Susceptibility tests on An. stephensi from Lahore with 5% malathion (1 hour exposure) showed an average survival of 68.95% indicating the presence of resistant individuals. Malathion resistance in An. stephensi from Pakistan is being herein reported for the first time. The gene(s) for malathion resistance was present in high frequencies in populations near Lahore. Selection for malathion resistance in the laboratory resulted in a 20 times increase after only three selected generations.
