Comparison of CDC Bottle Bioassay with WHO Standard Method for Assessment Susceptibility Level of Malaria Vector, Anopheles stephensi to Three Imagicides

Abstract

Background: The detection of insecticide resistance in natural populations of Anopheles vectors is absolutely necessary for malaria control. CDC bottle bioassay as a new tools has been employed for detecting the insecticide resistance. For a limit number of mosquito vectors, diagnostic doses and diagnostic times for some insecticides have already been deter­mined using this new assay. For the first time in the area, susceptibility levels of Anopheles stephensi was done with DDT, deltamethrin, and bendiocarb using CDC bottle bioassay and compared results with WHO standard test method.

Methods: Anopheles stephensi were collected in larvae stage from the cisterns of drinking water in Chabahar port which considered as old malaria foci, Sistan and Baluchistan province. The field collected larvae were colonized at the insectary of School of Public Health (SPH), Tehran University of Medical Science. The susceptibility tests were carried out on sugar fed female mosquitoes aged 2–3 days, against DDT 4%, bendiocarb 1% and deltamethrin 0.05% using WHO and CDC susceptibility methods. The mortality and knockdown rates, as well as the parameters of regression analysis, includ­ing LT₅₀ and LT₉₀, was calculated separately for the WHO and CDC methods. 

Results: The 24h mortality rates of An. stephensi were 28.6% and 25.6% for DDT, 60.8% and 64.6% for bendiocarb and 100% for deltamethrin using both WHO and CDC assay at 30 and 60min respectively. The 50% lethal times (LT₅₀) were estimated 44.9 and 66.2min, 38.9 and 81.8min and 0.7 and 15.0min respectively using both WHO and CDC susceptibility tests.

Conclusion: The similar results of susceptibility levels were shown for DDT, bendiocarb and deltamethrin. The lethal times (LT₅₀) showed significant difference using both WHO and CDC bioassay methods.