Which insect is responsible for chewing on plant roots?

The white grub is responsible for chewing on plant roots, making it the correct answer to this question. White grubs are the larvae of various beetle species and primarily feed on the roots of grass and other plants. Their feeding activity can cause significant damage to the root systems, leading to weakened plants, stunted growth, and even plant death in severe cases.

The other insects mentioned do not typically target plant roots. For instance, cutworms primarily feed on the above-ground portions of plants, typically severing seedlings at the soil level rather than targeting roots. Stink bugs are known for piercing the plant tissues and feeding on the sap, causing damage to fruits and leaves but not specifically to roots. Flea beetles also feed on the foliage, leaving characteristic holes in the leaves, and do not have a root-feeding behavior. Therefore, the white grub stands out as the clear choice for an insect that chews on plant roots.