Do ducks need to be dusted for bugs like chickens do. I don't know, I figured sense I never saw them dusting my guess would be, Not . Does the water take care of that???
Waterfowl don't normally need to be dusted. You are right, the water bathing takes care of it.
The only time you might need to lightly dust a duck is when for some reason they are unable to bathe on a regular basis and get some lice on them. I have a crippled ducks that I have to dust now and then, but just lightly. And always in a place she can't reach when preening.