What’s that white stuff on the prickly pear cactus?

I’ve heard people talk about the white stuff that appears on a prickly pear cactus pad but never knew for sure what it was.  Some said a fungus that would kill the plant.  Others said it could be washed off….but I never heard about it being caused by an insect.  After a few clicks on Google and Bing, I found the answer!  Thought you readers may be interested so am posting it here.  Very interesting.  Click on each page so it gets large enough for you to read.