  We comment on the presence of a bimodality in the distribution of delay time
between the formation of the progenitors and their explosion as type Ia SNe.
Two "flavors" of such bimodality are present in the literature: a "weak"
bimodality, in which type Ia SNe must explode from both young and old
progenitors, and a "strong" bimodality, in which about half of the systems
explode within 10^8 years from formation. The "weak" bimodality is
observationally based on the dependence of the rates with the host galaxy SFR,
while the "strong" one on the different rates in radio-loud and radio-quiet
early-type galaxies. We review the evidence for these bimodalities. Finally, we
estimate the fraction of SNe which are missed by optical and near-IR searches
because of dust extinction in massive starbursts.
