I am sorry to hear you are worried about Buddy. My name is Rebecca. I am a veterinarian and will do my best to help.
Drooling is a sign of nausea, pain, pancreatitis and dental diseaese (loose or infected teeth) in cats. It can also be from eating something that irritated the inside of his mouth so the ant powder might be the problem, although cats are notoriously finicky and usually do not eat things like ant powder. What is the name of the ant powder so I can look up its active ingredients?
Not eating really worries me; he might be getting dehdrated. Cats stop eating from dental disease, pain, fever, internal illnesses.
If you look at his gums, are they pale or a normal bright pink? Check him for dehydration: gently pinch skin over his shoulders and let it go; the skin should be back in normal position in less than one second. If it takes longer, he is dehydrated.
I am pretty worried about him. If I could, I would start with a thorough physical exam: listen to his heart and lungs with a stethoscope, palpate his internal organs and lymph nodes, take his temperature, check his gums, etc. That would be the first step of finding out what is wrong with him.
Let me know about his gum color and what other questions I can answer.