Question

what causes the pesticide treadmill?
the weakest pest individuals survive but die of starvation quickly after harvest.
pesticides exercise the pests, wearing them out, causing their bodies to become stronger.
pests that are not susceptible to pesticides no longer reproduce because they have more resources.
pest species evolve resistance via natural selection and more pesticide must be used on them.

Explanation:

The pesticide treadmill occurs when pest species evolve resistance through natural selection. As pests develop resistance, more pesticide is needed to control them, creating a cycle. The first option is incorrect as weak pests dying doesn't create a cycle. The second option is wrong as pesticides don't "exercise" pests. The third option is incorrect because pests that are resistant (not "not susceptible") reproduce more. The fourth option correctly describes the evolution of resistance via natural selection leading to the need for more pesticide.

Answer:

Pest species evolve resistance via natural selection and more pesticide must be used on them.