description fits azalea lace bugs. an internet search will yield photos.
the least toxic treatments would be horticultural oils or insecticidal soaps.

Whitish specks on the upper surface of leaves and dark spots varnish-like on the bottom are symptoms of rhododendron or azalea lace bugs, small insects with transparent wings on under-surface of leaves.. They are more prevalent on certain varieties and on plants grown in sunny areas. When damage first appears, it may be controlled by any of a number of contact insecticides such as Malathion or Orthene. Care must be taken to spray the lower surfaces of the leaves where the lace bugs live. Moving a plant to an area with more shade will alleviate the problem.