Which of the following is NOT an example of biological insect control?

Tillage of the soil does not fall under the category of biological insect control because it primarily refers to the agricultural practice of preparing the soil for planting by mechanically turning it over. This action is aimed at improving soil structure, controlling weeds, and enhancing crop establishment rather than directly managing insect populations.

In contrast, introducing natural predators, utilizing beneficial insects, and planting insect-resistant crops are all methods that focus specifically on managing pest populations using biological methods. These strategies involve leveraging natural ecosystems: natural predators help keep pest numbers in check, beneficial insects aid in pollination and pest management, and insect-resistant crops have been developed to withstand or repel specific pests, reducing the need for chemical pest control measures. Thus, tillage is the option that does not fit the biological control framework.