I am not a Washington State lawyer, but most states have adopted some form of a uniform landlord tenant law. You need to find out if, (and I think it may be), the failure to rid your apartment of these bed bugs is a denial of essential services. If indeed it is, you can pay for the extermination and deduct that from your rent. You ought to call the health department and ask what sort of problems are caused by bed bugs. I do think it can be serious if it continues. Call a legal aid clinic and ask whether this infestation would be a denial of essential services, and save your receipts.
Morgenstern & Herd
WA's Residential landlord-tenant act is Chapter 59.18 RCW. The statutes can be read at: http://apps.leg.wa.gov/RCW/default.aspx?cite=59.18 .
If you are in the city limit of Seattle, Seattle has more stringent ordinances. The Seattle housing inspectors may be useful.
Among the landlord's duties as given in RCW 59.18.060 is: "(4) Provide a reasonable program for the control of infestation by insects, rodents, and other pests at the initiation of the tenancy and, except in the case of a single family residence, control infestation during tenancy except where such infestation is caused by the tenant;"
You wrote that you "now have bed bugs". Does that mean that when you moved in there were no bed bugs? If yes, were the bedbugs brought into the apartment by you?
Have you talked with your neighbors? Do they also have bedbug problems? My understanding is that bedbugs are becoming more prevalent again. Powerful chemicals must be used to kill the bedbugs. Unless all infected areas are treated at the same time, the bedbugs will just hide in the untreated areas until the chemicals are no longer toxic to the bedbugs.
If you have a rental agreement, the rental agreement may have clauses relating to your situation. The RLTA also provides what the landlord or tenant may do in some situations.
Landlord/tenant law can be complex. You may want to consult an attorney to review your facts and options.