  A method of Parity-Time (PT)-symmetry analysis is introduced to study the
high dimensional, complicated parameter space of drift wave instabilities. We
show that spontaneous PT-symmetry breaking leads to the Ion Temperature
Gradient (ITG) instability of drift waves, and the collisional instability is
the result of explicit PT-symmetry breaking. A new unstable drift wave induced
by finite collisionality is identified. It is also found that gradients of ion
temperature and density can destabilize the ion cyclotron waves when PT
symmetry is explicitly broken by a finite collisionality.
