  Weak gravitational lensing observations probe the spectrum and evolution of
density fluctuations and the cosmological parameters which govern them. The
non-linear evolution of large scale structure produces a non-Gaussian signal
which is potentially observable in galaxy shear data. We study the three-point
statistics of the convergence, specifically the bispectrum, using the dark
matter halo approach which describes the density field in terms of correlations
between and within dark matter halos. Our approach allows us to study the
effect of the mass distribution in observed fields, in particular the bias
induced by the lack of rare massive halos (clusters) in observed fields. We
show the convergence skewness is primarily due to rare and massive dark matter
halos with skewness converging to its mean value only if halos of mass M >
10^15 M_\sun are present. This calculational method can in principle be used to
correct for such a bias as well as to search for more robust statistics related
to the two and three point correlations.
