You could try Rain X bug and tar remover.
I bought some on a whim because I had some neglected bug spatters baked on the car.
It sprays on and stays put - let it sit for 5 minutes or so and, viola! the bugs come off easily while doing a wash job.
It seems to have a lot of petroleum base to it as it'll kill a sudsy bucket of car wash QUICK!
I do the bug laden parts first, kill the washing soap and then get new sudsy water to do the rest of the car with. I even used it to clean the brake dust on my Bimmer - hey, it didn't do half bad!
Sorry for being so gate mouthed!!! Cheers! DV