  We present measurements of the bispectrum of dark matter halos in numerical
simulations with non-Gaussian initial conditions of the local type. We show, in
the first place, that the overall effect of primordial non-Gaussianity on the
halo bispectrum is larger than on the halo power spectrum when all measurable
configurations are taken into account. We then compare our measurements with a
tree-level perturbative prediction finding good agreement at large scale when
the constant Gaussian bias parameter, both linear and quadratic, and their
constant non-Gaussian corrections are fitted for. The best-fit values of the
Gaussian bias factors and their non-Gaussian, scale-independent corrections are
in qualitative agreement with the peak-background split expectations. In
particular, we show that the effect of non-Gaussian initial conditions on
squeezed configurations is fairly large (up to 30% for f_NL=100 at redshift
z=0.5) and results from contributions of similar amplitude induced by the
initial matter bispectrum, scale-dependent bias corrections as well as from
nonlinear matter bispectrum corrections. We show, in addition, that effects at
second order in f_NL are irrelevant for the range of values allowed by CMB and
galaxy power spectrum measurements, at least on the scales probed by our
simulations. Finally, we present a Fisher matrix analysis to assess the
possibility of constraining primordial non-Gaussianity with future measurements
of the galaxy bispectrum. We find that a survey with a volume of about 10 cubic
Gpc at mean redshift z ~ 1 could provide an error on f_NL of the order of a
few. This shows the relevance of a joint analysis of galaxy power spectrum and
bispectrum in future redshift surveys.
