  We perform fully-kinetic particle-in-cell simulations of an hot plasma that
expands radially in a cylindrical geometry. The aim of the paper is to study
the consequent development of the electron temperature anisotropy in an
expanding plasma flow as found in a collisionless stellar wind. Kinetic plasma
theory and simulations have shown that the electron temperature anisotropy is
controlled by fluctuations driven by electromagnetic kinetic instabilities. In
this study the temperature anisotropy is driven self-consistently by the
expansion. While the expansion favors an increase of parallel anisotropy
($T_\parallel>T_\perp$), the onset of the firehose instability will tend to
decrease it. We show the results for a supersonic, subsonic, and static
expansion flows, and suggest possible applications of the results for the solar
wind and other stellar winds.
