@Yen1 - this is your second post in just a few minutes asking how much to charge for items which are regarded as wear and tear. You really can’t go around charging guests for every minor thing.
Now that you know that the guest is eating in his room and (presumably) you’ve put a stop to it, then an ant infestation is unlikely to happen.
However, if your home is prone to ants, then presumably you have some ant gel in your cleaning cupboard already so why would you charge the guest?
The security deposit certainly wouldn’t cover it because the guest has to agree that they caused the ‘damage’ and it’s highly unlikely that you can prove that they did. What’s interesting though is that you’re asking about a situation that hasn’t even happened yet!