  We investigate the evolution of primordial black hole mass spectrum by
including both accretion of radiation and Hawking evaporation within
Brans-Dicke cosmology in radiation, matter and vacuum-dominated eras. We also
consider the effect of evaporation of primordial black holes on the expansion
dynamics of the universe. The analytic solutions describing the energy density
of the black holes in equilibrium with radiation are presented. We demonstrate
that these solutions act as attractors for the system ensuring stability for
both linear and nonlinear situations. We show, however, that inclusion of
accretion of radiation delays the onset of this equilibrium in all radiation,
matter and vacuum-dominated eras.
