Management of insecticide resistance in the major Aedes vectors of arboviruses: Advances and challenges
Fig 2
Flow chart to support decision-making of IRM strategy during implementation of a vector control program.
The first process deals with resistance monitoring within the target insect population. The second process is the monitoring of treatment efficacy that should be run in parallel with process 1. It aims to detect any control failure and whether it is caused by resistance or other external factors. Risk levels are defined according to the results of resistance monitoring and should trigger graduated and appropriate response: (i) level 0 indicates a population fully susceptible to the insecticide, (ii) level 1 designates a population whose susceptibility is maintained but some of whose individuals harbor resistant alleles, (iii) level 2 corresponds to a moderate resistance (e.g., RR below 5 or below 98% mortality using 5 times the WHO DC), (iv) level 3 corresponds to populations clearly resistant to a given insecticide and that require immediate IRM strategy (e.g., RR above 5 or below 98% mortality using 10 times the WHO DC). According to the current knowledge gap, molecular or biochemical assays cannot be straightforwardly used to define IRM levels (except from level 0 to level 1), and basically, these levels are defined using the bioassays. The resistance thresholds for levels 2 and 3 are only indicative and fixed by analogy to the last WHO procedures [33]. They should be refined according to operational-based evidences. For levels 2 and 3, the characterization of resistance mechanisms is requested to guide a decision on alternative insecticides and to follow the impact of IRM on the frequency of resistance alleles. DC, diagnostic concentration; IR, insecticide resistance; IRM, insecticide resistance management; Mort, mortality; RR, resistance ratio.