  We report the frequency-dependent conductivity of the manganite system
La1-xSrxMnO3 (x <= 0.2) when approaching the metal-insulator transition from
the insulating side. Results from low-frequency dielectric measurements are
combined with spectra in the infrared region. For low doping levels the
behavior is dominated by hopping transport of localized charge carriers at low
frequencies and by phononic and electronic excitations in the infrared region.
For the higher Sr contents the approach of the metallic state is accompanied by
the successive suppression of the hopping contribution at low frequencies and
by the development of polaronic excitations in the infrared region, which
finally become superimposed by a strong Drude contribution in the fully
metallic state.
