Evaluating rotations as a strategy to delay the evolution of insecticide resistance in vectors of human diseases.

IntroductionInsecticide resistance threatens the control of important human vector-borne diseases such as malaria and dengue. The current de facto strategy is to target the insect vectors using a sequential deployment of insecticides i.e. use one insecticide (usually the cheapest available) until resistance has made it ineffective and then replace it with the next insecticide in the repertoire. Rotations of insecticides are often advocated as a potentially superior method of using the insecticide repertoire to delay the evolution of resistance. Testing this hypothesis in the field is logistically demanding and an in silico approach offers a much faster, flexible and transparent method of evaluating rotations. MethodsWe develop an in silico approach to evaluate rotations using sequential deployment as the baseline. We explored a wide range of deployment scenarios, underlying genetics of resistance, and incorporated costs of resistance and gene flow to/from untreated refugia. ResultsWe found that, under most circumstances, resistance to all the insecticides in the repertoire were reached at very similar times for rotations and sequences. Any advantages of one strategy over the other tended to be small (typically <10%) and unpredictable. ConclusionsOperational factors, such as cost or supply-chain security, may therefore largely determine the optimal choice of insecticide deployment strategies.