are there any kashrut problems with the chemically treated oranges (since they have e-904 on their skin and according to a kosher list e-904 needs a hechsher)?
It would seem that e-904 called shellac which partially derived from the female lac bug, on trees in the forests of India and Thailand would be problematic as it comes from a non kosher bug. However the poskim give numerous reasons why it is permitted. Firstly, it is not actually from the bug, rather it is extracted from the trees, similar to the honey in a bee. Another reason is because the shellac is not digestible and tasteless and therefore it isn’t considered food, rather like a rock.