Hybridization experiments with Culex fatigans from the Philippine Islands and North American strains of C. fatigans, pipiens, and molestus showed that the Philippine mosquito is interfertile with the American populations. Low hatching in F1 egg rafts from the Philippine female x pipiens male cross was probably due to reduced mating activity; larvae from the rafts which did hatch, and larvae from all other crosses, developed normally. Survival rates of the hybrid larvae and pupae were comparable to those of the parent strains. All F1 hybrids produced vigorous F2 and backcross colonies.
It is concluded that C. fatigans from Luzon in the Philippine Islands is conspecific with C. pipiens, molestus, and fatigans from North America.