Sometimes individuals at one extreme of a phenotypic distribution are favored in a particular environment, for example, selection will strongly favor insects that have very high resistance to an insecticide. In such cases, the type of selection that operates is

directional

Explanation:

We define directional selection as a type of natural selection whereby a phenotype is favored in preference to other phenotypes hence, the entire allele in the population will tend to shift in that particular direction .

This is clearly demonstrated in a scenario whereby insects that have very high resistance to an insecticide tend to survive better in an environment compared to other insects that do not exhibit this phenotype.