Although my colleagues answer (Mitchell's below) is normally the case, you always need to go back first to the contract and its terms. Lately, contracts have been drafted in some states (and I am not familiar with yours) where the buyers essentially get what is sometimes called "a free look" -- a euphemism for "if you don't like what you see in the inspection, either you or the seller can walk if the seller doesn't want to fix or remediate."
I will say it is not usually the case if there has been "prior" infestation, because that should have been disclosed, and the company who had done the prior treatment could be pressed to come back and treat again. Unfortunately, it always "depends" on what the paperwork says.
All that said, if your realtor is persistent and assertive, usually that pays off and the seller will fix it, especially in today's market, so I would strongly urge you to have your broker go to the seller or the seller's broker or attorney and push to get it taken care of. They just need to make sure they are armed with as much knowledge as possible.
Good luck. I hope this helps.
Carol T. Wilsey,
Exceptional Properties of SW Florida