when you say self regulating, would this mean the food plant of the silkworms would be planted inside the container? if so, you have to think whether the plant (and the silkworms at that, since i don't know anything about their care) would be ok with the heat and temperature the mantids would want/need. anothe rthing to think about is how quickly silkworms grow in size, much quicker than mantids, so the silkworms would only be of the right size for a short while before they grow too big. or if the mantids were of the right size to catch the adults, you would need to have silkworms/moths at various different stages of growth to make sure there is a regular supply of moths. i think i read that the female silkmoths are too heavy and small-winged to fly, so they may not come into contact with/get eaten by the mantids. i dont really know what hornworms are so cant really say, but i would guess some of the same issues would arise with them.
i have never kept roaches but from what i gather they cannot jump or fly (at least, the ones commonly kept as feeders). so if they are exclusively ground dwelling, they wouldnt really be suitable for your purposes i would imagine. i think they like to hide too right? maybe if you found a species more keen on flying about? to be honest i think what you want to achieve would be quite difficult to do with mantids. i think your best bet is some type of caterpillar/moth/butterfly species with similar condition requirements. however to maintain a rolling cycle population of them would need (i imagine) a very large food plant. however, if adding branches of foodplant into the enclosure every so often still counts as self regulating then your options are alot wider.
would be interesting to see what you decide on, keep us informed!
