Ramon Applies a Chemical Pesticide to His Corn Crop to Help

Ramon applies a chemical pesticide to his corn crop to help protect against yield loss due to insect pests. Initially, the treatment is successful as most of the insect pests are killed off. However, after a few seasons of growing the same crop and applying the same pesticide, Ramon observes that the treatment is losing its effectiveness against these pests. Use your understanding of evolutionary principles to explain to Ramon what has happened.