  We report on a hierarchy of temperatures Tc < Tgap < Tmet in superconducting
Rb1-xFe2-ySe2 observed by THz spectroscopy. Above Tmet = 90 K the material
reveals semiconducting characteristics. Below Tmet a coherent metallic THz
response emerges. This metal-to-insulator type, orbital selective transition is
clearly indicated by an isosbestic point in the temperature dependence of the
optical conductivity and dielectric constant at THz-frequencies. At Tgap = 61 K
a gap opens in the THz regime and then the superconducting transition occurs at
Tc = 32 K. This sequence of temperatures seems to reflect a corresponding
hierarchy of the electronic correlations in the different bands.
