Answer: The insects you describe sound like whiteflies, but I've never seen them attack roses before. It could also be leafhoppers--small, wedge-shaped insects which hold their wings in a little "roof" over their backs. Both these insects will cause leaf drop--but they won't kill a healthy plant in a few days. I have a feeling something else is at work here. Have you had a very wet spring? Or are the plants located in a place with poor drainage? (Or the opposite--have the plants had adequate water all spring?) It sounds more to me like something to do with water and/or disease than insect attack. Plants sitting in waterlogged soil suffer root rot. The plant can endure a certain amount of saturation, but at some point the roots lack the necessary oxygen and die, causing the aboveground plants to rapidly decline.
If you think the insects did indeed cause the damage, I might try to take a sample (in a tighly sealed bag!) to a local nursery for positive ID. Insecticidal soaps are effective against whiteflies and leafhoppers, but you need to saturate both the tops and the undersides of the leaves to get the adults, nymphs and eggs. It often takes multiple sprays to get the population down to a manageable size. There are predacious wasps that feed on whiteflies, so if you use a chemical, you'll kill the beneficial wasps as well. Try hosing your plants off with plain water every few days, being thorough and hitting all plant parts with the water. Or, you can make yellow sticky traps that will attract the whiteflies but not harm the beneficial insects. Take bright yellow cardboard or index cards and smear with petroleum jelly. Suspend the traps from stakes placed among the infested plants. The whiteflies will be attracted to the yellow color and will become entrapped on the sticky surface. Replace the traps when they're no longer sticky, or when they're full. You just have to be persistent in your method of control and eventually you'll be the victor!
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