Holly Bush-Infested

A friend of mine has two well established Holly bushes (over 20 yrs old). They both have a white, rice shaped thing stuck to the leaves (kind of bug or disease). They are infested. I sprayed 4 times with Malathion. It does not seem to be doing much. Do you know what it is and how do I treat it? She wants to save them if she can. Nothing else around it seems to be infected.