Piercing-sucking mouth parts are most commonly found in which of the following groups?

Piercing-sucking mouthparts are specialized adaptations that allow certain insects to feed on the fluids of plants or other organisms. True bugs, which belong to the order Hemiptera, are known for possessing these mouthparts, which they use to puncture plant tissues and extract sap or to feed on the blood of hosts in the case of some parasitic species.

Flies, while they can have various mouthpart structures, often have specialized forms suited for different feeding habits, but it is primarily the true bugs that exemplify piercing-sucking mouthparts effectively. Other groups like caterpillars, grasshoppers, beetles, ants, butterflies, and moths do not possess this type of mouthpart. Instead, they have chewing mouthparts or, in the case of butterflies and moths, a proboscis adapted for sucking nectar rather than piercing to suck fluids from a host directly. Therefore, the group that is best associated with piercing-sucking mouthparts is true bugs, making the selection appropriate.