What is generally a key feature of rodenticides?

Rodenticides are specifically designed to control rodent populations, which is why the response indicating their primary purpose is correct. These substances work by targeting rodents, either by causing them to ingest a toxic dose or by interfering with their bodily functions in a way that leads to death. This targeted approach is essential for managing pest populations effectively, particularly in areas where rodents can cause significant damage or pose health risks.

The other choices do not accurately represent the purpose of rodenticides. For instance, while some products might be designed with environmental considerations in mind, many rodenticides can have negative impacts on non-target species and the environment. Additionally, rodenticides do not specifically target moths, nor are they used for insect control, as their effectiveness is limited strictly to rodents.