Kristin, the 'newt bites' that you buy in a store are poor in terms of nutrition. Just as with any pet, you need to offer them foods that have the required nutrients. These pellets are lacking and are not a good food. Salamanders are carnivores and need to eat meat, usually in the form of earthworms and general insects.
Also, you do realize that in Michigan, the collection of wild salamanders is only legal if you possess a fishing license.