Which of the following approaches to biological control uses pathogens?

The approach that uses pathogens in biological control is represented by suspensions of spores. This method specifically involves using the spores of various microorganisms, such as fungi or bacteria, which can infect and kill unwanted plant species or pests, thereby serving as a natural means of controlling their populations.

Using pathogens leverages the natural disease cycles found in the environment to target specific aquatic weeds, allowing for a more sustainable control method. This is significant in an ecosystem where maintaining a balanced environment is important, as it reduces reliance on chemical pesticides that may have adverse environmental effects.

Other methods mentioned, such as the hydrilla tuber weevil, involve biological control through herbivory rather than pathogens. Mechanical removal and hand removal are physical methods that do not involve any biological agents, making them less effective in the context of utilizing natural biological interactions to manage invasive species.