It's because variations exists in individuals among a species. The more "insecticide resistant" insects survive, while those which are non-resistant die. Those resistant ones reproduce to produce a large population of insecticide resistant insects.
Natural selection eliminates those which cannot adapt to the environment those which can adapt are retained.
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It's because variations exists in individuals among a species. The more "insecticide resistant" insects survive, while those which are non-resistant die. Those resistant ones reproduce to produce a large population of insecticide resistant insects.
Natural selection eliminates those which cannot adapt to the environment those which can adapt are retained.