Answer:
The given case is an illustration of natural selection. Natural selection refers to the phenomenon on the basis of which the organisms that get amended with the environment, seem to thrive and generate more offspring. The theory was first postulated by Charles Darwin and is now considered to be the prime reason, which results in evolution.
Similarly, in the given question, the insects who could withstand the environment around them continue to reproduce, in comparison to those who could not cope up with the environment, thus, this would be regarded as an illustration of natural selection.