Methods in Anopheles Research - MR4

Chapter 5 : Insecticide Resistance5.1 Insecticide Resistance Bioassays5.1.3 Guidelines for Evaluating Insecticide Resistance in Vectors using the CDC Bottle BioassayPage 22 of 24µg/bottle is the toxicological saturation point for insecticide entering the mosquito and reaching its target.Increasing the concentration to 25 µg/bottle does not cause the insecticide to penetrate the mosquito,reach the target site, and kill the mosquito any faster. Therefore, 15 µg/bottle is the saturation point andthe maximum concentration to use as the diagnostic dose. Otherwise, there is a risk that resistantmosquitoes will be killed by doses higher than the saturation point and then be recorded as susceptible,i.e., false negatives for resistance.A slightly smaller concentration compared to the toxic saturation point will kill mosquitoes in an amount oftime perhaps more convenient for the user (e.g., 30 to 60 minutes). So, it is possible to choose a lowerdiagnostic dose that kills 100% of mosquitoes within 30 to 60 min. It must be understood that severaldifferent pairs of diagnostic doses and diagnostic times will give interpretable results, but it is necessaryto consistently use the same diagnostic dose and diagnostic time for that particular insecticide on thatvector in future assays over long periods of time to allow for comparability. Otherwise, the method will notallow assessment of changes in resistance over time for that species.Figure 5.1.3.4: Determining diagnostic doses and diagnostic times.In the example shown below, 15 µg/bottle is the saturation point because higher doses did not decreasethe time for 100% of susceptible mosquitoes to be killed. A concentration of