i culture flightless fruit flies(really easy to do and in time youll have ready supply if decide to expand your collection) so just tap them into each mantis tub(well nymphs) i find it easier to culture fruitflies than crickets,
for larger mantids i feed bluebottle,green bottle and houseflies along with feeding them turkistan roaches etc (variety of foods always works well ive found)
ghosts are amazing mantids,best of luck with your mantids