The "Culex pipiens pipiens" bioform of "Culex pipiens" usually inhabits areas above ground and targets avian species. The "Culex pipiens molestus" bioform, on the other hand, usually inhabits underground cavities and targets human hosts. When these two bioforms hybridize, the progeny shows depolarization in both habitat and host preferences. As a result, these hybridized species play a role in disease transmission. This is because avian species amplify diseases such as West Nile virus. A hybridized mosquito can become infected by feeding on an avian amplifier and then feed on a human, effectively passing on West Nile pathogens to that human.