How is pesticide resistance developed in pests?

Pesticide resistance in pests primarily develops through the mechanism of natural selection, especially when pesticides are overused or misused. When a pesticide is applied, most of the pest population may be killed off, but some individual pests may possess or develop genetic traits that confer resistance to that specific pesticide. These surviving pests, due to their resistant traits, are then able to reproduce and pass these traits on to their offspring. Over time, this leads to an increasing proportion of the pest population that is resistant to the pesticide.

This process is exacerbated by frequent or inappropriate applications of the pesticide. For instance, if a pesticide is used repeatedly without intervention or rotation with other pest management strategies, it gives resistant individuals a continual opportunity to thrive and reproduce.

The other options provided do not accurately explain how pesticide resistance specifically develops. Crossbreeding typically plays a role in genetic diversification but does not directly lead to resistance from pesticide application. Environmental changes can influence pest populations but are not a direct cause of resistance development. Similarly, the introduction of new pest species may alter the ecosystem but does not contribute to the existing pests developing resistance to pesticides.