IMO if you can afford to feed this, crushed turtle pellets would be a good gut load for them.
I use a high end dog food for most of my feeder bugs, I have SO many that I can't afford high dollar reptile pellets which aren't all that far removed from dog food anyway.
I also use whole grain cereals & bread, left overs from my parrot's organic pellets, the cricket quencher gel stuff with calcium added for moisture & fresh greens too. I like the cricket quenchers better than a slice of apple or potato or whatever because then I don't get fruit flies in the house & the crickets seem to stay alive for a longer period of time since I started using it.
500 for 4 bucks, man you got a DEAL! 
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PHRatz