The simulation measurements of suprathermal ions and low frequency electric field signals at the ionopause of Venus by Pioneer Venus instruments suggests that they may be causally related. Linear Vlasov theory is used to examine both parallel and perpendicular propagating waves for instability in the presence of planetary ions added to the flowing ionosheath plasma. For the low &bgr; plasma conditions found near the ionospause, neither electrostatic (ion acoustic) nor electromagnetic (whistler) parallel propagating waves are found to be unstable. Perpendicular propagating electrostatic (Bernstein) waves are found to be quite unstable and to have the proper frequency-wavelength relation to be Doppler shifted into the observed 100-Hz frequency channel. The growth rates can be substantial, and the instability occurs for a wide range of ionosheath conditions. It is difficult for an electric field measurement to distinguish between these waves and electromagnetic waves such as whistlers. Planertary ions are probably thermalized only after several gyroperiods so that they may be easily observed only well down-stream from the planet.