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We check the performance of the {\sl\,PARSEC} tracks in reproducing the blueloops of intermediate age and young stellar populations at very lowmetallicity. We compute new evolutionary {\sl\,PARSEC} tracks of intermediate-and high-mass stars from 2\Msun to 350\Msun with enhanced envelope overshooting(EO), EO=2\HP and 4\HP, for very low metallicity, Z=0.0005. The input physics,including the mass-loss rate, has been described in {\sl\,PARSEC}~V1.2 version.By comparing the synthetic color-magnitude diagrams (CMDs) obtained from thedifferent sets of models with envelope overshooting EO=0.7\HP (the standard{\sl\,PARSEC} tracks), 2\HP and 4\HP, with deep observations of the Sagittariusdwarf irregular galaxy (SagDIG), we find an overshooting scale EO=2\HP to bestreproduce the observed loops. This result is consistent with that obtained by\citet{Tang_etal14} for Z in the range 0.001-0.004. We also discuss thedependence of the blue loop extension on the adopted instability criterion andfind that, contrary to what stated in literature, the Schwarzschild criterion,instead of the Ledoux criterion, favours the development of blue loops. Otherfactors that could affect the CMD comparisons such as differential internalextinction or the presence of binary systems are found to have negligibleeffects on the results. We thus confirm that, in presence of core overshootingduring the H-burning phase, a large envelope overshooting is needed toreproduce the main features of the central He-burning phase of intermediate-and high-mass stars.

Envelope Overshooting in Low Metallicity Intermediate- and High-mass Stars: a test with the Sagittarius Dwarf Irregular Galaxy