Answer:
Directional selection
Step-by-step explanation:
Directional selection may be defined as a type of natural selection in the extreme phenotype is favored by the nature. The allele frequency will shift in one direction only.
In case of insecticide resistance, the insects that will develop resistivity against insecticides will grow, develop, reproduce and favors by nature. They will pass down their beneficial allele to the next generation. Only insecticide resistance insect will be extreme in the population and other insects of the population will die.
Hence, the correct answer is option D.