A verandah-trap hut for studying the house-frequenting habits of mosquitoes and for assessing insecticides. IV. The effect of tetramethrin on the behaviour and mortality of Anopheles gambiae Giles

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Abstract
The effects of tetramethrin on the behaviour and mortality of Anopheles gambiae Giles entering verandah-trap huts have been studied with the assistance of gaschromatographic techniques.Fifty-three to 39% of A. gambiae were deterred from entering a corrugated-iron-roof hut treated indoors with a nominal dosage of 2 gm/m2 tetramethrin active ingredient.Overall mortalities were 53–71% in the first month of application, but fell two to three months after application to 22–46%.The tetramethrin deposit had marked effects on the behaviour of A. gambiae entering treated huts. Feeding was greatly inhibited, 69–90% of the mosquitoes being unfed. Also, as the residual toxicity of the deposit declined, increasingly higher proportions (40–70%) of recently blood-fed A. gambiae left the huts due to the irritant action of the insecticide. The chemical basis of the irritant effect was indicated to the extent that survivors leaving the treated hut showed 9·5–14·0 ng tetramethrin/individual. The minimum lethal dose was indicated by 17·5–21·7 ng/individual picked up by mosquitoes showing delayed mortalities after leaving the treated huts. Mosquitoes that died indoors picked up amounts ranging from 27·0 to 42·3 ng/individual.The effects of tetramethrin on A. gambiae were in general similar to those of DDT and pyrethrum, and differed only in degree.