In the context of an insect repellent that comes as a creme or lotion, both "anwenden" and "auftragen" can describe the same action. But the basic meanings of the verbs are different.
"Anwenden" has a more basic meaning like "to apply". "Auftragen" in this context means something like "to spread (something on something)" or "to coat (something with something)". In other contexts, "auftragen" can have additional meanings, for example with hand-me-down clothes ("er trägt den Pullover seines älteren Bruders auf") or with assignments ("sie trägt ihm auf, den Hof zu kehren").
So if your insect repellent is a creme or lotion or something similar, you can apply ("anwenden") it by spreading it ("auftragen") on your skin. But if the insect repellent is, say, a spray, you would apply ("anwenden") it by spraying ("einsprühen") yourself with it.
"Anwenden" has, of course, a much broader spectrum. You could for example apply a mathematical operation to a data set, "eine mathematische Operation auf einen Datensatz anwenden". In this case, there's (hopefully) no smearing involved at all ;)
And as others have already said, "gilten" isn't a proper German word, there's probably some misunderstanding involved here.