Which insect's larvae feed inside leaves, creating tunnels that cause discoloration?

Leafminers are the correct answer because their larvae develop inside the tissues of leaves, specifically between the upper and lower leaf surfaces. As these larvae feed on the leaf’s internal layers, they create distinct tunnels or mines that are visible as discolored pathways on the leaves. This damage not only affects the aesthetic appeal of the plant but can also hinder its ability to photosynthesize effectively, potentially leading to further health issues for the plant.

In contrast, mole crickets primarily feed on the roots and the soil around the plants, causing damage by burrowing and disrupting root systems rather than creating visible leaf damage. Thrips are tiny insects that tend to feed on the surface of leaves and can cause stippling and distortion rather than the tunneling associated with leafminers. Lace bugs, on the other hand, generally feed on the undersides of leaves and cause a different type of damage characterized by stippling and a declining overall appearance of the foliage, rather than the tunnel-like mines of leafminers.