Who is responsible for insuring public artworks after they have been created and installed?

This varies considerably by program and by location.  Most commonly, states or art agencies self-insure the work they produce (many are required to do so by their percent for art law).  Some states transfer insurance duties to the owners of the artworks they produce, which are typically other city agencies or private companies.  Occasionally, additional insurance funding may be sought out to protect specific collections or high-value objects.