Serpentine or blotchy streaks or blisters on the underside of leaves indicate what type of infestation?

Serpentine or blotchy streaks or blisters on the underside of leaves are characteristic symptoms of a leafminer infestation. Leafminers are larvae of certain insects that burrow between the upper and lower leaf surfaces, creating visible trails or mines as they feed. These mines often appear as winding, serpentine lines or blotchy areas, which distinguish them from damage caused by other pests.

In comparison, scale insects typically produce a hard shell or scale on the leaves, leading to discoloration or a sticky residue rather than the distinctive trails seen with leafminers. Spider mites tend to cause stippling or speckling on the leaves due to their piercing-sucking mouthparts, but this does not create the same type of visual damage as leafminers. Aphids can cause curling and distortions of leaves, but their feeding does not produce the serpentine patterns indicative of leafminer activity. Thus, the unique visual symptoms associated with an infestation of leafminers makes it the correct identification in this context.