Who covers the cost of professional treatment
In California, the landlord generally pays for professional bed bug treatment, because keeping the rental sanitary and habitable is the landlord's duty and bed bugs spread through the building.
Effective bed bug treatment — often heat treatment or repeated professional visits — is expensive and technical, and it usually needs to cover neighboring units as well. That makes it the landlord's responsibility, not the tenant's. Tenants are expected to cooperate by preparing the unit and reporting the problem promptly, but they should generally not have to pay for treating a building infestation.
Attempts to blame and bill a single tenant are common, but they are often unfair given how easily bed bugs travel between units. If your landlord is trying to charge you for treatment that should be their responsibility, a free review can help you understand what is fair.
This is general information about California tenant rights, not legal advice. Every situation is different.