Make a 50/50 solution of peroxide and water. Spray on the bugs and let it sit for about 10-15 mins. You'll see the bugs foaming - like blood foams when you put peroxide on a cut - because it reacts with protein. This will soften them and most should come off. If real heavy, you might have to do it again.
Another method is to wet a towel in hot water and lay it on the surface. Leave it for a minute or two and then they should wipe right off.
I have a motorcycle and am OC with keeping it glistening. These methods work better than any expensive spray cans off the shelf.