Cinara spp.
See:
Pest description and crop damage The aphids that infest junipers are large insects, up to 0.2 inch long. Color may range from gray to brownish to dark. The aphids establish large colonies on the twigs but rarely are found feeding on scales.
For more information
Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 82).