Following are the three ways in which an insect pest can attack the crop plants:

1. Chewing insects: They destroy all kinds of crop plants by cutting root, stem, and leaf of plants with their chewing mouth parts.

Examples: Locusts, grasshoppers, etc.

2. Sucking insects: They destroy the crop plant by sucking the cell sap from its various parts.

Examples: Aphids, leaf hoppers, etc.

3. Internal feeders: They live inside the parts of plants. These are called borers (if they live in twigs or roots) or weevils (if they live in fruits and seeds).

Examples: Pod borers and grain weevil.