Loveeeeee keeping ghosts. I use D. hydei fruit flies when they are this small.
In a few molts when they start gaining size I switch to blue bottle flies. They thrive on this diet.
You can buy pupa and food for the flies online. They hatch quickly but are tricky to get out individually. For this, I throw the container in the freezer until the flies deactivate. Then I will pick the amount I need and put them in the mantis habitat. After a few minutes in the warmth the flies will reactivate.