Resistant levels of houseflies to six kinds of synthetic insecticides in the Philippines.

The resistant levels of houseflies to six kinds of insecticides: DDT, Pyrethrins, malathion, Sumithion, Baytex and DDVP, were examined on 15 strains collected in the Philippines. It was found that most housefly colonies in the Philippines showed higher susceptibility to those insecticides than the Takatsuki strains, especially to DDT. The range of LD50 values to malathion were between 1.775 microgram and 0.0975 microgram per fly. Among 15 strains collected in the Philippines, 7 showed higher LD50 values to malathion than the Takatsuki strain. These values mean that the houseflies in the Philippines are increasing their resistance to malathion.