With the limited facts you provide, it will be hard to provide a solid answer. But, for the purposes of general discussion only, a landlord is required to maintain the unit in a good state of repair. This includes addressing issues that affect the habitability of the unit, such as bed bugs. However, the landlord is only responsible if the bed bugs are not due to your actions (such as keeping an unsanitary unit). Based on the facts you provide, it appears as though the bed bugs arrived before you moved in. If that is the case, then the landlord had an obligation to remove them before you arrived and if he did not, then he must remove them now. This condition affects your habitability and he is responsible accordingly. I am only licensed in CA and this answer should not be viewed as legal advice.