Which of the following is a characteristic of sucking insects?

Sucking insects are distinguished by their specialized mouthparts, which are adapted for feeding on the sap and cellular fluids of plants. These mouthparts, often elongated and needle-like, allow these insects to penetrate plant tissues efficiently and extract nutrient-rich fluids. This feeding behavior can lead to various plant health issues, including wilting, stunted growth, and transmission of plant pathogens.

The other options, while they address aspects of insect behavior, do not accurately describe the characteristics of sucking insects. Chewing insects, for instance, use mandibles to bite and consume plant material rather than extracting fluids. Feeding exclusively on roots pertains to another group of insects and is not characteristic of all sucking insects. Additionally, while many sucking insects can indeed be harmful, there are also non-harmful species that coexist with plants. Thus, the correct answer highlights the defining feeding mechanism of sucking insects, which is their use of specialized mouthparts for sap extraction.