  The annihilation of dark matter (DM) particles in the Milky Way can
contribute to the diffuse gamma-ray background (DGRB). Due to the presence of
substructures, this emission will appear anisotropic in a predictable way. We
generate full-sky maps of the gamma-ray emission in galactic substructures from
results of the high-resolution Via Lactea II N-body simulation of the Milky Way
DM halo. We calculate the anisotropy pattern, taking into account different
radial profiles of the DM distribution in substructures, cosmic variance, and
the detection threshold, and compare it to the anisotropy in the DGRB observed
by the Fermi Large Area Telescope (LAT). By comparing the upper limits on the
DM self-annihilation cross-section, <$\sigma v$>, implied by the anisotropy to
the intensity of the DGRB and detected sources in the LAT 2-yr Point Source
Catalog, we find that galactic substructure cannot contribute to the
anisotropies in the DGRB without strongly violating these observations. Our
results challenge the perception that small-scale anisotropies in the DGRB can
be used as a probe of DM annihilation in galactic subhaloes.
