In every lease there is an implied warranty of habitability which requires the landlord to maintain the premises in a habitable condition by complying with local and state housing codes.  When there is a breach of the implied warranty of habitability, the tenant notifies the landlord as you have done and the landlord is required to respond within a reasonable time by making the necessary repairs.  When the landlord fails to respond within a reasonable time, the tenant has the following options:  The tenant can make the repairs (contact an exterminator in your case) and deduct the cost from the rent or the tenant can move out and terminate the obligation to pay rent for the balance of the term of the lease or if the tenant remains on the premises, the tenant can withhold rent and defend against eviction.  Another alternative is to sue the landlord for breach of the implied warranty of habitability.  The bug infestation is a health issue and therefore is a breach of the implied warranty of habitability.  Another alternative is to contact the local housing code inspector who can take action against the landlord to comply with the housing code.