But here's what "Yahoo Answers" offers as it's best answer to what are the little green worms that are devouring my rose bushes: Not trying to be a wise guy, but they're Baby moths.
If you want to get rid of them, buy the insecticide specified to target them and read the label carefully to ensure optimal effectiveness.
If you care enough about the environment to ensure the poison doesn't eventually work it's way into our already strained clean water supply, (and it will) wait a few days and their natural predators (wasps) will appear and kill them for you. The wasps that target them are not aggressive like the ones that build those huge sized paper nests. They live in small holes in rotting dead wood. You can make a few your self by drilling 1/2 inch holes in a section of 2X4 or a branch you find lying around in your yard. Hang them approximately 50-100 feet away from your house and the wasps will help you out. If allergic (Pick-em off by hand or use the poison responsibly)
I would pick them off by hand until the wasps figure out where they are.
Had the same question a few years ago, did the research and built a couple of simple and easy to make wasp habitats in my back yard. The wasps won't bother you and it's fascinating to watch them hover around the plant then suddenly drop down on one of the little critters and fly away with it.
So there we go! Now, I've learned something valuable, and pass on this tip to you...and now I'm going out to the garden to wash the white stuff off and get rid of it, probably onto a brush pile with lots of water so it will be so dilute it won't hurt anything...
And - I'm going to enjoy the rose blooms! Hope you have a "rose-y" day!