Etched into the clearcoat, or just dried hard as cement on top of the clear? Anyways, dilluted APC, a boar's hair brush, and pressur ewasher usually does it. Clay also works. Another option is a the yellow bug block that feels rough as sand paper, but when soaked in warm water becomes much softer and can be used in combination with your wash solution or APC. If the bug residue actually etched into the clear, it would have to be compounded or maybe even wet sanded.