Ant Problem that wont go away..whose responsibility?

[softmonkey]

You have gone far above and beyond your duty with two pest treatments, this is sufficient documentary evidence that you have tried to address the problem, and it is clear that the tenant is the cause. Do not throw any more good money after bad.

Your tenant may have lived in a different climate or well-sealed house in the past and may simply need to be educated about sealing food in containers and clearing food bins daily. This plus a couple of natural deterrents like cinnamon powder and vinegar/water spray have always worked for us.

PS - during the worst heatwave I had truly desperate ants come in just for water from the sink, though the kitchen was pristine and there was not one scrap of food to be found. In this case we did resort to a can of bug spray squirted directly into the floorboard crack they were using.