We have lived in our condo for 4 years and we've never had a problem with bugs. Just this last month we have been getting bit from bed bugs and we are OVER it. We're sure it is from one of the adjacent condos. (A lot of people moving in and out) Our landlord said she'd pay for the 1st treatment but no more! It takes more than one to get rid of this problem! We had our first one last week and are still getting bit. We will spray again this month and for a few more. We don't think we should pay for it. It is her property.
In many apartment buildings this is truly a building problem. Unfortunately, Colorado is a state where the landlords aren't regulated as they might be for problems like this.
The first thing is to WRITE a letter to the landlord. Make the complaint and make sure to describe the issues and the ineffectiveness of the first treatment. Letters count, almost no other kind of notice does.
Second, at the same time that you write the Landlord, call and WRITE the local county health department and make a complaint. Tell the county that the building is infested and the landlord is refusing to fix the problem.
Third, call the city, if you are in a city. Most city's also have ordinances that apply, and yo may well get a code enforcement officer who can cite the landlord.
Finally, unless you want to pay for treatments yourself, you could move claiming the LL breached the lease. Once you've done all of the above AND CAN PROVE YOU DID THEM WITH PAPER, NOT JUST YOUR WORD, then you can move out and defend the LL's keeping the security deposit and suing you for lost rent.
If you go to move out, you should try to negotiate your leaving with the LL or consult an attorney.