  We study the implication of the collapsar model for Long Gamma-Ray Bursts
(LGRBs) on the metallicity properties of the host galaxies, by combining
high-resolution N-body simulations with semi-analytic models of galaxy
formation. The cosmological model that we use reproduces the Fundamental
Metallicity Relation recently discovered for the SDSS galaxies, whereby the
metallicity decreases with increasing Star Formation Rate for galaxies of a
given stellar mass. We select host galaxies housing pockets of gas-particles,
young and with different thresholds in metallicities, that can be sites of LRGB
events, according to the collapsar model. The simulated samples are compared
with 18 observed LGRB hosts in the aim at discriminating whether the
metallicity is a primary parameter. We find that a threshold in metallicity for
the LGRB progenitors, within the model galaxies, is not necessary in order to
reproduce the observed distribution of host metallicities. The low
metallicities of observed LGRB hosts is a consequence of the high star
formation environment. The star formation rate appears to be the primary
parameter to generate a burst event. Finally, we show that only a few LGRBs are
observed in massive, highly extincted galaxies, while these galaxies are
expected to produce many such events. We identify these missing events with the
fraction of dark LGRBs.
