For years I fought potato bugs. I sprayed and dusted. I even planted marigolds between the plants and they just kept munching the leaves. They developed an immunity to insectacides and learned to love the stench of marigolds. I put up bird houses in hopes of attracting insect eaters. Nada. Then I learned the trick. You just knock the little gluttons off the plants. Spraying them with a hefty stream of water will do it. Once on the ground, they don't have sense enough to climb back up on the plants.
You have to do it every 3 or 4 days until the plants begin to fade, but if you do a good job, you get bushels of spuds. Try it!
Now I need to find an easy way to dig them.
Howard