  We present a seismic study of $\delta$ Scuti based on a mode identification
from multicoulor photometry. The dominant frequency can be associated only with
a radial mode and the second frequency is, most probably, a dipole mode. The
other six frequencies have more ambiguous identifications. The photometric mode
identification provided also some constraints on the atmospheric metallicity
[m/H]$\approx$+0.5 and microturbulent velocity $\xi_t\approx 4~\kms$.\\ For
models reproducing the dominant frequency, we show that only the fundamental
mode is possible and the first overtone is excluded. However, the location of
$\delta$ Scuti near the terminal age main sequence requires the consideration
of three stages of stellar evolution. For the star to be on the main sequence,
it is necessary to include overshooting from the convective core with a
parameter of at least $\alpha_{\rm ov}=0.25$ at the metallicity greater than
$Z=0.019$. It turned out that the value of the relative amplitude of the
bolometric flux variations (the nonadiabatic parameter $f$) is mainly
determined by the position of the star in the HR diagram, i.e., by its
effective temperature and luminosity, whereas the effect of the evolutionary
stage is minor. On the other hand, the convective efficiency in the
subphotospheric layers has a dominant effect on the value of the parameter $f$.
%in the $\delta$ Sct star models. Comparing the theoretical and empirical
values of $f$ for the radial dominant mode, we obtain constraints on the mixing
length parameter $\alpha_{\rm MLT}$ which is less than about 1.0, independently
of the adopted opacity data and chemical mixture. This value of $\alpha_{\rm
MLT}$ is substantially smaller than for a calibrated solar model indicating
rather low to moderately efficient convection in the envelope of $\delta$
Scuti.
