Several strains of a mosquito, Anopheles albimanus Wiedemann, were synthesized that allow the preferential elimination of females during any of the 4 life stages. This genetic sexing system utilizes propoxur susceptibility as a recessive conditional lethal, a T(Y;2R) translocation, and an In(2R) inversion. The propoxur resistance allele (dominant) was linked to the Y chromosome via a radiation-induced translocation and subsequent genetic recombination was suppressed by inversions. In one of the strains produced, 99.8% of the females were eliminated when treated with propoxur without male loss. Chemically sterilized males of one strain were found to be fully competitive for mating in a laboratory cage.