Insecticide resistance is arguably the greatest current threat to the future of malaria control and to the sustainability of the achievements of recent years. The science of Resistance Prevention and Management is a major consideration of ours when developing new products and initiatives worldwide.
Basics about resistance
Insecticide resistance is defined as an inheritable trait which confers reduced susceptibility to an insecticide or group of insecticides. There are a number of different mechanisms which can be involved.
Insecticides do not generate resistance mutations in insects, but pre-existing mutations can be selected out and come to dominate a mosquito population if the same selection pressure (or insecticide mode of action) is maintained over a prolonged period. In extreme circumstance resistance can result in insecticide-based control measures being ineffective.
In order to main insecticide susceptibility it is therefore important to proactively implement a resistant management strategy which involves exposing mosquitoes to different modes of action, and to adopt integrated vector management, with techniques which do not involve insecticides at all. Without such approaches the selection for, and expansion of, insecticide resistance is a real and pending threat.
Up until 2018 malaria vector control relied on only four different chemical classes of insecticides (organochlorines such as DDT, organophosphates such as pirimiphos-methyl, carbamates such as bendiocarb and pyrethroids such as deltamethrin, permethrin and alpha-cypermethrin). As a result resistance can be found to almost all of those insecticide classes (not always simultaneously).
Since 2018, three new insecticide classes have been introduced for malaria control (neonicotinoids, pyrroles and juvenile hormone analogues) and a brand new mode of action recently introduced by Bayer for Aedes mosquito control (butenolide chemistry – flupyradifurone, contained in the space spray Fludora Co-max).
There is increasing scope to be able to manage resistance with these additional modes of action and increasing willingness of country programs to pro-actively adopt resistance management strategies.