  We discuss the results about the nature of type Ia Supernovae that can be
derived by studying their rates in different stellar populations. While the
evolution of SN photometry and spectra can constrain the explosion mechanism,
the SN rate depends on the progenitor system. We review the current available
data on rates as a function of parent galaxy color, morphology, star formation
rate, radio luminosity and environment. By studying the variation of the rates
with the color of the parent galaxy, a strong evidence was established that
type Ia SNe come from both young and old stars. The dependence of the rates
with the radio power of the parent galaxy is best reproduced by a bimodal
distribution of delay time between the formation of the progenitor and its
explosion as a SN. Cluster early-type galaxies show higher type Ia SN rate with
respect to field galaxies, and this effect can be due either to traces of young
stars or to differences in the delay time distribution.
