If extraterrestrials had a human bait to rid the Earth of people, what would it be?

Thinking about the growing ant problem before it became an indoor ant problem; I had seen some ant bait strips. When reading how they worked, because I wanted something passive that would kill off the hive and work without my active involvement, the instructions said to place it where the ants would find it, they will eat it and poison themselves, plus take some back to the hive and poison them and the queen thus killing the hive off. I was thinking if extraterrestrials were able to observe us undetected as I was undetected to the ants, and introduce some poison to mankind that would be readily accepted without suspicion, and carried around from community to community infecting each one, what would the extraterrestrials use? It has to be something humans would want and use/eat, undetectable as a toxin or agent of death, be communicable enough to reach infect anyone coming near. What could the extraterrestrials use to assure we doom ourselves?