When feeding my 4 inch pseudopimelodus bufonius he seems to only accept the food when I wiggle it around in his face, do any of you know if this normally happens with this species? My old 8 inch one did not have this problem with feeding.
Not particularly unusual; I've seen Pseudopimelodus spp. refuse everything but live foods before.
They don't 'scavenge' as much as other catfish (and are typically more inactive overall). More inclined to ambush small fishes (even congeners and difficult-to-digest species like loricariids and Corydoras!)
The smaller size will likely have some impact, too- it seems like larger individuals are somewhat less picky about what they eat.
The good thing is that the fish is eating in the first place- that's oftentimes the most difficult step to overcome. I'd assume he'll start taking food without you wiggling it around as he grows.