Insecticide resistance is a term used to describe the situation in which mosquitoes are no longer killed by the standard dose of an insecticide (i.e., they are no longer susceptible to the insecticide) or manage to avoid coming into contact with the insecticide.
In mosquitoes, insecticide resistance is mediated by multiple resistance mechanisms and is an evolutionary phenomenon. There is consensus that resistance will eventually emerge to any insecticide that continues to be widely used.
The objective of Insecticide Resistance Management (IRM) is to preserve or prolong the susceptibility of mosquito vectors to insecticides, in order to maintain the effectiveness of insecticide-based vector control interventions. The four main strategies used in IRM are:
- Rotations – switching between insecticides with different modes of action at pre-set time intervals, irrespective of resistance frequencies.
- Mosaics – deployment of insecticides of different modes of action in neighbouring geographical areas.
- Mixtures – formulations that combine two or more insecticides with different modes of action.
- Combinations – combinations expose the vector population to two classes of insecticides with differing modes of action through co-deployment of different interventions in the same place (e.g. pyrethroid Long Lasting Insecticidal Nets (LLINs) combined with a non-pyrethroid Indoor Residual Spray (IRS).