Susceptibility Studies on Anopheles culicifacies with DDT and Dieldrin in Gujarat State, India1

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Abstract
Susceptibility tests with DDT and dieldrin on adult Anopheles culicifacies Giles and with DDT on the larvae have been conducted in Panchmahals district of Gujarat State, India, where resistance of the adults to DDT was encountered in 1959-60. Intensive testing of the susceptibility of the adults to DDT was carried ont from October 1960 to May 1962 at approximately monthly intervals. The results indicated a progressive rise in the level of DDT resistance with LC30S than 4% in almost all instances. The variations in the number of the sprays applied at some talukas of the district have resulted in verying sensitivities. At the 4% DDT concentration, mortalities ranging between 2.5 and 6.3% were obtained at the regularly sprayed part of Motipura village in Daria taluka, while mortalities ranging between 17.5 and 55.7% were recorded at Rampura village in Godhra taluka, which had fewer rounds of spraying. Lowered suscepti-bilities appeared also in districts other than Panchmahals, but the sensitivities there varied according to the spray histories. An LC50 1.5% was recorded at a village in Kaira district which had 5 years of residual DDT spraying, while at villages in Ahmedabad district, which had 12 years of spraying, LC50S 4% were found. Lengthening the exposure period to 8 hours at Omidpura and Mandhra villages in Panchmahals district in no instance resulted in 100% mortality at the 4% DDT concentration. The results showed fluctuations in the resistance levels which are fairly comparable at the 2 villages. The weather was most likely responsible for these fluctuations. Larvae of A. culicifacies were susceptible to DDT with LC50S ranging between 0.10 and 0.14 ppm. Adults exhibited susceptibility to dieldrin; the LC50S ranged between 0.052 and 0.17% of dieldrin.

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