  Pulsational properties of 1.8 M$_{\odot}$ stellar models covering the latest
stages of contraction toward the main sequence up to early hydrogen burning
phases are investigated by means of linear nonadiabatic analyses. Results
confirm that pre-main sequence stars (pms) which cross the classical
instability strip on their way toward the main sequence are pulsationally
unstable with respect to the classical opacity mechanisms. For both pms and
main sequence types of models in the lower part of the instability strip, the
unstable frequency range is found to be roughly the same. Some non-radial
unstable modes are very sensitive to the deep internal structure of the star.
It is shown that discrimination between pms and main sequence stages is
possible using differences in their oscillation frequency distributions in the
low frequency range.
