If the electron distribution function is approximately bi-Maxwellian with T⊥/T∥>1, where the subscript symbols denote directions perpendicular and parallel to the background magnetic field, and if this temperature anisotropy is sufficiently large, the whistler anisotropy instability is excited. This mode is studied using two-dimensional particle-in-cell simulations in a spatially homogeneous plasma model. Theory predicts a threshold electron anisotropy for this instability which depends inversely on the electron parallel &bgr;. The simulations show that wave-particle scattering by enhanced whistler fluctuations maintain the initially bi-Maxwellian character of the electron distribution, and that this scattering imposes an upper bound on the electron T⊥/T∥ commensurate with that predicted by linear theory. ¿ American Geophysical Union 1996