Isopods are slow to breed and slow to grow so they don't make ideal breeders. Turkistan roaches are a good choice if your dubias are not breeding fast enough for you, they breed at a much faster rate than dubias, still maintain that bonus of higher protein than crickets (and dubias but not by much). Turks don't climb smooth surfaces and don't burrow in substrate, and they are a smaller species than dubias, adults reaching the size of an adult cricket, and mature in 3-5 months vs a dubia is 6 months to maturity (another factor why dubias are slow to breed). The downfall, they are quick little suckers!
I also want to note that depending on the diet you are offering any species of roach can greatly vary their production. A good quality diet NOT including any dog/cat food is best for them, although people say high protein, they in fact need a diet of 15% protein or less to stay healthy. And when on a well balanced diet their production rate is better (higher birth rate).
Silkworms are always a nice choice, they grow quickly, they have the most protein out of all the popular feeders, you can easily store eggs in the freezer and pull them out to incubate them. The downfall they need a specialized diet.
