[Jeir]

The food I would recommend for those in North America would be the Tiny Friends Farm Hazel Hamster Tasty Mix. The Harry Hamster version we have here in the UK is pretty much the same thing, and is what I've been feeding my hamsters for twenty years (as well as a species-specific Rodipet mix, but it's rather expensive).
The Vitakraft mix you currently have is okay, but it seems to be mostly alfafa, which most hamsters ignore. If you wish to continue with this mix, it's up to you.
As for mealworms/insects, I've never had a syrian interested in those, but most of my dwarf hamsters did like them. Things like cooked, plain chicken has always gone down well, though.