The bottom-left panel shows the models calculated with $Z=0.015$, OPAL tables and convective overshooting parameter $f=0.02$. The bottom-right panel depicts models calculated with element diffusion. Details of the used mass-loss models and implementation of diffusion are described later in this section. Similarly to our previous results (D2013) there is the p- and g-mode instability beyond TAMS for the models that undergo hydrogen shell burning. Most of the unstable modes are non-radial, but the radial fundamental mode is also unstable in hotter models beyond main sequence.

The main difference between our current and all previous calculations is the presence of unstable non-radial modes on the blue loops for more massive models ($M \gtrsim 14 M_\odot$ and $\log T_\mathrm{eff} \gtrsim 4.2$). The radial modes are stable in this evolutionary stage in all calculated models. The existence of pulsation instability on the blue loop, as well as the blue loops themselves, depend critically on the metallicity, $Z$. With lowering the metallicity the blue loops reach the higher effective temperatures which has a huge impact on pulsation instability. In models with the lower value of $\log T_\mathrm{eff}$ the driving layer related to the metal opacity bump is located too deep in the star to 