Purple python, you might try offering seeds and oats and whole grain cheerios as treats rather than fruits and veggies. Rats and mice rarely eat fruits and vegetables naturally, and most can have minor negative effects (bloating, diarrhea) on their digestive systems (few can have very bad effects, but none are especially good for rats and mice).

Whole grain cheerios (the sugar free kind) are a real big hit with most rodents!
I would also recomend not using a vegetarian dog treat, but going with a natural freeze dried chicken kind instead (if you're looking for something natural). The meat is healthy for them, and they really like them.
The mealworms are definitely good for them! Crickets are fun too, it's great to see the rodents turn into wild animals and chase crickets around!