  We calculate the cosmic microwave background temperature bispectrum from
cosmic strings, for the first time including the contributions from the last
scattering surface, using a well-established Gaussian model for the string
energy-momentum correlation functions, and a simplified model for the cosmic
fluid. We check our approximation for the integrated Sachs-Wolfe (ISW)
contribution against the bispectrum obtained from the full sky map of the
cosmic string ISW signal used by the Planck team, obtaining good agreement. We
validate our model for the last scattering surface contribution by comparing
the predicted temperature power spectrum with that obtained from a full
Boltzmann code treatment applied to the Unconnected Segment Model of a string
network. We find that including the last scattering contribution has only a
small impact on the upper limit on the string tension resulting from the
bispectrum at Planck resolutions, and argue that the bispectrum is unlikely to
be competitive with the power spectrum at any resolution.
