Abstract
Houseflies have been collected at 14 spots scattered in 9 prefectures in the Tohoku, Hokuriku and San'in areas, and their levels of sensitivity to 8 kinds of insecticides were studied. The results are shown in Table 1. It was found that the houseflies in all 14 spots showed a decline of sensitivity to Malathion and fenitrothion. Malathion LD_<50> : Nagai-city colony, 21.826μg∿Takizawa colony, 131.513μg. Fenitrothion LD_<50> : Koyama-cho colony, 0.849μg∿Morioka-city colony, 16.557μg. However the houseflies did not show any decline of sensitivity to dichlorvos (DDVP) and resmethrin.
