Ok, i'm a car valeter and to get bugs off, i use Auto Glym Engine and Machine cleaner - will get anything off and is safe to use on pretty much anything (including chrome, polished etc) just dont do it on a hot surface i.e. a black car thats been left baking in the sun for 6 hours, do it in the shade and don't let it dry, not a major issue if it does, can just leave streaks which will polish out.
BUT - If you have a cheap polish like Halfrauds Best Super Duper Value Wash N' Wax or Polish it will take it straight off so you will need to re apply polish after use.
Then follow it up with Auto Glym Super Resin polish (this has a very fine cut to it) then if you want to do a propper job follow up with Auto Glym Ultra Deep Shine (filling polish) Then apply a Hard Wax or Liquid Hard Wax... And if that doesn't do the trick nothing will! Engine cleaner is also ace for your windscreen for all the bugs and crap you dont need a lot of it.
Hope this helps!:thumbsup: