  An analytic equilibrium, the Toroidal Bessel Function Model, is used in
conjunction with the gyrokinetic code GYRO to investigate the nature of
microinstabilities in a reversed field pinch (RFP) plasma. The effect of the
normalized electron plasma pressure ({\beta}) on the characteristics of the
microinstabilities is studied. A transition between an ion temperature gradient
(ITG) driven mode and a microtearing mode as the dominant instability is found
to occur at a {\beta} value of approximately 4.5%. Suppression of the ITG mode
occurs as in the tokamak, through coupling to shear Alfven waves, with a
critical {\beta} for stability higher than its tokamak equivalent due to a
shorter parallel connection length. There is a steep dependence of the
microtearing growth rate on temperature gradient suggesting high profile
stiffness. There is evidence for a collisionless microtearing mode. The
properties of this mode are investigated, and it is found that curvature drift
plays an important role in the instability.
