  The evolution of the electron heat flux in the solar wind is regulated by the
interplay between several effects: solar wind expansion, that can potentially
drive velocity-space instabilties, turbulence and wave-particle interactions,
and, possibly, collisions. Here we address the respective role played by the
solar wind expansion and the electron firehose instability, developing in the
presence of multiple electron populations, in regulating the heat flux. We
carry out fully kinetic, Expanding Box Model simulations and separately analyze
the enthalpy, bulk and velocity distribution function skewness contributions
for each of the electron species. We observe that the key factor determining
electron energy flux evolution is the reduction of the drift velocity of the
electron populations in the rest frame of the solar wind. In our simulations,
redistribution of the electron thermal energy from the parallel to the
perpendicular direction after the onset of the electron firehose instability is
observed. However, this process seems to impact energy flux evolution only
minimally. Hence, reduction of the electron species drift velocity in the solar
wind frame appears to directly correlate with efficiency for heat flux
instabilities
