Piercing and sucking insect pests are a type of insect that feed on the sap or juices of plants. To do this, they possess specialized mouthparts that allow them to pierce the plant and suck out its fluids. The specific mouthparts they have are called probosces.
Probosces are a type of elongated mouthpart that function like a straw, allowing the insect to penetrate the plant's surface and extract fluids. They are often long and slender, and may be curved or flexible to help the insect navigate around obstacles and reach different parts of the plant.
In contrast, mandibles, maxillae, and labrums are mouthparts found in other types of insects, such as chewing insects. These mouthparts are used to cut, crush, and grind plant material before it is consumed.
Therefore, the correct answer to the question is: Probosces.