Over many generations, certain insect species have become more and more resistant to insecticides. what type of natural selection does this show and how does it differ from the other types?

The type of natural  selection that is described here is called a simple positive selection.We know this because positive selection is the process by which new advantageous genetic variants sweep a population or remain resistant. This type of selection is known when insects have greater endogenous resistance, with the insecticide being the selective agent.