Which of the following is NOT a natural control method in aquatic pest management?

Chemical pesticides are synthetic substances used to control pests, which makes this option distinctly different from the other choices that focus on natural methods of pest management. Natural control methods aim to manage pest populations through ecological processes rather than applying man-made substances.

The introduction of predator species involves bringing in natural predators to keep pest populations in check. This method utilizes the natural food web to control pests without chemical intervention.

Encouragement of native species is another natural approach, as native plants and animals can help maintain ecological balance and compete with or reduce populations of invasive pests.

The natural evolution of pest species is an ongoing process wherein pests adapt to their environment. While it can influence pest populations and management strategies, it is not an active control method applied by humans.

In contrast, the use of chemical pesticides is a direct intervention that can disrupt local ecosystems and lead to unintended consequences, making it the clear choice that does not align with natural control methods.