In this paper we study the evolution of the resonance zones that appear in connection with a Hopf-pitchfork bifurcation exhibited by a Z2-symmetric electronic circuit. These regions, bounded by curves of folds (saddle-node bifurcations) may be closed or open depending on the values of the parameters. An angular degeneracy on the torus bifurcation curve originates the banana shape of Arnold's tongues. The presence of homoclinic bifurcations is also pointed out.

The analysis of the Takens-Bogdanov bifurcation of the equilibrium at the origin in the Chua's equation with a cubic nonlinearity is carried out. The local analysis provides, in first approximation, different bifurcation sets, where the presence of several dynamical behaviours (including periodic, homoclinic and heteroclinic orbits) is predicted. The local results are used as a guide to apply the adequate numerical methods to obtain a global understanding of the bifurcation sets. The study of the normal form of the Takens-Bogdanov bifurcation shows the presence of a degenerate (codimension-three) situation, which is analyzed in both homoclinic and heteroclinic cases.