I am would be reluctant to do unilateral poison treatments. People have very different (mostly emotional) reactions to this stuff. I would consider their feeling about poisons…and the risk of them squawking about it.

Mostly, I agree with what UC gal said, but with the tenant agreeing to any toxic remedy, if needed. From the start of the first episode, I would be nudging the tenant towards not bothering me about average seasonal occurrences of ants or other bugs.As someone else said, I would never ask a landlord to deal with average ant problems.