I have lived in this apartment for 7 months, which is one of 4 in a duplex. This duplex used to be a rooming house for low income sober living 2 month prior to me moving in. I started noticing about 2 months ago a rash on my arms and legs, which I thought was dry skin, but it has worsened leading me to look into it more. As it turns out I am allergic to bed bugs. I have never experienced this rash or anything like it before, here, or any where I have lived so that leads me to believe someone has brought them into the duplex,my landlord expects me to pay for and treat my apartment, but if it is an issue from downstairs should the whole place not be treated? Rather then me waste my place being treated by more bugs from the other unit?

Your lease will tell you if your landlord is to pay for pest control. Otherwise, you may need to review your local Landlord/Tenant Law.

Is it in the contract? I live in an apt community that has a very specific lease contract in which it states that they are responsible for extermination.

Read yours. If it does not spell it out, then you are responsible.

The entire duplex does need to be treated at the same time, else the exterminator's warranty can be voided. Bedbugs require a very thorough treatment. You will need to negotiate with your landlord and your neighbor regarding payment resposibilities. Laws differ from locale to locale, but remember if you move out not all the bugs will go with you.

I think the basic position is that if it is not spelled out in the lease, that the landlord has the default requirement to provide safe and sanitary housing, but the tenant has to do his part to keep it clean, etc. It may be a multi-unit issue that the landlord can be held responsible for, but do you want to go to small claims over it? Cats is right that this is something that you should negotiate with your landlord. At the very least you will have to talk to the landlord. The landlord may surprise you and it won't be an issue. Find out more by searching "landlord tenant rights pest control" or "landlord responsibility pest control" for more information.