We compute the electromagnetic dispersion relation for right- and left-hand circularly polarized low frequency waves propagating parallel and antiparallel to the upstream interplanetary magnetic field in the presence of both reflected and diffuse suprathermal ions. The ion distribution function is modeled after three-dimensional observations of reflected and diffuse ions made upstream of the quasiparallel bowshock crossing of December 8, 1977, while the electron distribution function is based on concurrent three-dimensional observations of low energy electrons. It is found that the reflected ions destabilize the plasma most strongly at &ohgr;~0.1&OHgr;i by way of a resonant ion beam instability for waves propagating upstream, and by way of a nonresonant firehose-like instability for waves propagating downstream. The diffuse ion population also destabilizes the plasma most strongly at &ohgr;~0.1&OHgr;i by way of resonant instability of both right- and left-hand polarized waves propagating away from the bow shock. The growth times of the unstable waves are roughly 60 s and 150 s for those associated with the reflected and diffuse ions, respectively, during which time the waves would be carried several earth radii downstream.