  We examine the superfluid-Mott insulator (SF-MI) transition of
antiferromagnetically interacting spin-1 bosons trapped in a square or
triangular optical lattice. We perform a strong-coupling expansion up to the
third order in the transfer integral $t$ between the nearest-neighbor lattices.
As expected from previous studies, an MI phase with an even number of bosons is
considerably more stable against the SF phase than it is with an odd number of
bosons. Results for the triangular lattice are similar to those for the square
lattice, which suggests that the lattice geometry does not strongly affect the
stability of the MI phase against the SF phase.
