It's mostly earthworms here. My culture seems to have an endless supply of worms. I haven't got an extreme collection, but I've got over 50 adult mouths to feed which I do every two days. Other food items are cultured roaches, cultured white worms, tubifex, crickets, wc slugs, wc snails and other wild caught invertebrates.
Still I use pellets to raise T.dobrogicus and P.waltl larvae. I've got special aquatic newt pellets, but they were a bit too expensive (I'm Dutch) if you ask me. I've also used sturgeon pellets with succes. I never use frozen food.