Gas? Holy Cow. I take it you don't wax your car.
I'd just use a cleaner wax or possibly a polish. It has a bit of abrasive in it to actually scour the stain away.
If the car is worth waxing....I suggest after you get all the bug gunk off of it, apply 2 coats of ReJex (at least 12 hours apart) onto clean paint....which means washing the car well with Dawn dish soap or Simple Green, drying the car well, and then applying the product.
It's the best. It's cheap. It works really really well. You can also wax on top of it. But don't apply ReJex over wax.