  We present deep Near-infrared (NIR) images of a sample of 19
intermediate-redshift ($0.3<z<1.0$) radio-loud active galactic nuclei (AGN)
with powerful relativistic jets ($L_{1.4GHz} >10^{27}$ WHz$^{-1}$), previously
classified as flat-spectrum radio quasars. We also compile host galaxy and
nuclear magnitudes for blazars from literature. The combined sample (this work
and compilation) contains 100 radio-loud AGN with host galaxy detections and a
broad range of radio luminosities $L_{1.4GHz} \sim 10^{23.7} -
10^{28.3}$~WHz$^{-1}$, allowing us to divide our sample into high-luminosity
blazars (HLBs) and low-luminosity blazars (LLBs). The host galaxies of our
sample are bright and seem to follow the $\mu_{e}$-$R_{eff}$ relation for
ellipticals and bulges. The two populations of blazars show different
behaviours in the \mnuc - \mbulge plane, where a statistically significant
correlation is observed for HLBs. Although it may be affected by selection
effects, this correlation suggests a close coupling between the accretion mode
of the central supermassive black hole and its host galaxy, that could be
interpreted in terms of AGN feedback. Our findings are consistent with
semi--analytical models where low--luminosity AGN emit the bulk of their energy
in the form of radio jets, producing a strong feedback mechanism, and
high--luminosity AGN are affected by galaxy mergers and interactions, which
provide a common supply of cold gas to feed both nuclear activity and star
formation episodes.
