Relative Efficacy of Different Synthetic Pyrethroid Impregnated Fabrics (ITNs) on Knock Down Time of Anopheles Stephensi

Abstract

We aimed to evaluate the efficacy of different fibers of bednets impregnated with various pyrethroids and the efficacy of LD50,LD90 and diagnostic dose of pyrethroids on median knock down time of susceptible strain of An.stephensi . The other aim of the present study was to determine distribution of knock down time values (Standard Division). Bioassey test was carried out with simple netting apparatus under laboratory condition using a new method of WHO proposed by Curtis. 11 female mosquitoes were released into net apparatus and median knock down time of them were calculated for each type of pyrethroids and fabrics. their standard division ( SD ) and Standard error ( SE ) were calculated exactly by Probit analysis of Finney. Results showed Median knock down time in 10 mg.m-2 dosage of lambdacyhalothrin on polyester, nylon and cotton net was calculated as 3.1, 3.5 and 6.3 minutes respectively. It was calculated in 20 mg.m-2 dosage of deltamethrin on polyester , nylon and cotton net, as 6.6, 8.7 and 21.7 minutes respectively. In 40 mg.m-2 dosage of cyfluthrinon on polyester , nylon and cotton net, It was calculated as 6.3, 7.5 and 19.9 minutes respectively . Finally in 200 mg.m-2 dosage of etophenprox on polyester , nylon and cotton net, It was calculated as 10.6, 12.5 and 7.4 minutes. It was seen direct relationship between LD50, LD90 and diagnostic dose of pyrethroids and median knock down time. Lambdacyhalothrin had the least value of LD50 (10 mg.m-2 ), LD90 and D.D, created the least value of knock down time in comparison with other pyrethroids. Etophenprox had the highest value of LD50 (200 mg.m-2), LD90 and D.D, created the highest value of knock down time. Deltamethrin and cyfluthrin had intermediate values. Also there was a reverse relationship between dosage of pyrethroids and median knock down time. Polyester net need the least concentration of pyrethroid, shown the least values of knock down time and the least LD50, LD90 and diagnostic dose. So it is the best suitable net for impregnation. In all doses of all pyrethroids on all type of nets, median knock down time was similar to the knock down time of the 6th mosquito ( mode ). These values were the closest value to the KDT50.