How to confront messy roommates?

I live with one girl in my room, and then two other girls (who I have very little contact with and do not know really at all) share my kitchen and living room. For some reason, these girls do not know how to properly dispose of food. When they pour out dishes of food, such as ramen, they simply leave the noodles in the sink, instead of sending them down the garbage disposal. They've left things such as pizza boxes sitting for a week or more at a time. My actual roommate is not QUITE as bad, but her trash is nasty, and she sometimes carelessly leaves open food items in our room. Now aside from it just being gross and irritating, we have a bad ant problem, and now I'm actually starting to get bit in my sleep. I want to talk to these girls in a way which gets me results, rather than provoke them and in turn get nothing, if not a worse outcome. I was thinking of leaving a note in the kitchen, but what exactly should I say, etc.?