DDT and gammexane as residual insecticides against Anopheles gambiae in African houses

Experimental mud and thatch huts, with window traps attached, have been used to compare the effect of house treatment with residual insecticides against Anopheles gambiae in East Africa. In huts treated with DDT water dispersable powder at the rate of 400 mg. DDT per square foot (twice the normal dose), large numbers of gambiae can feed in the treated hut and escape alive. Of those that leave the treated hut at least 98 per cent. are alive after 24 hours, and at least 80 per cent. after 48 hours. The number of A. gambiae found dead inside the treated hut is only about 1 per cent. of those that escape alive after feeding. Attempts to increase the kill by screening window openings have only met with limited success. Similar huts treated with B.H.C. in the form of “gammexane” dispersable powder, P. 530 at the rate of 24 mg. gamma isomer. per square foot, have proved completely lethal to all gambiae entering for at least 13 weeks after treatment. During that time there is no indication of any gambiae escaping unharmed from the hut. The number of dead blood-fed and unfed gambiae found regularly on the floor sheets is proof of continued lethal action for at least 3 months after treatment. The superiority of gammexane over DDT in control of A. gambiae is so clearly marked that it is the obvious insecticide on which to concentrate.