  This paper deals with the problem of location and existence of limit cycles
for real planar polynomial differential systems. We provide a method to
construct Poincar\'e--Bendixson regions by using transversal conics. We present
several examples of known systems in the literature showing different features
about limit cycles: hyperbolicity, Hopf bifurcation, sky-blue bifurcation,
rotated vector fields, \ldots for which the obtained Poincar\'e--Bendixson
region allows to locate the limit cycles. Our method gives bounds for the
bifurcation values of parametrical families of planar vector fields and
intervals of existence of limit cycles.

Dynamical Systems