You can feed crawling insects to them easily, like waxworms, hornworms, silkworms, or mealworms (although they don't really like mealworms much due to low moisture content and the exoskeleton). Orchid mantids (and all mantids really) can eat anything they can catch, unless it is toxic of course. None of them have specialized mouthparts (unless you count pedipalps, which aren't unique to mantids), and people mainly feed flying insects because the mantids take them easily without hand-feeding and their raptorial arms are much better adapted to capture prey without the obstruction of ground.
Anyways, waxworms IMO are the ideal prey for mantids if you want to feed them more infrequently. However, many mantids aren't attracted to them unless significantly hungry, so you should make a small puncture in the waxworm (which is very easy to do) or cut off it's head. Either way, fluids will seep out when the waxworm tries to move and you touch the worm to the mantis's mouthparts. They'll testing it with their pedipalps, then nibbling temporarily, then they'll grab the worm from you and start eating like there's no tomorrow! Not to mention, one of my favorite things about them is you can either feed the fatty, water-providing, soft larvae or the fatty, extremely tempting moth!
Also, roaches and locusts are great food too! Although they're harder to feed than waxworms due to it being harder to expose their flesh without being disgusted, and you'll generally need to feed more frequently due to their lower fat levels. However, depending on the type, you might not even need to "prepare" the food. I've noticed mantids have an extreme fetish for green prey, so you could get a colony of Panchlora nivea or find some green orthopterans! I'd recommend not feeding crickets though. WAAAY too many strange stories about them.
However, remember, mantids all have varying levels of aggression and hunger and you might not need to prepare the food or the mantis may reject it totally for a minute and if so, try again after any small amount of time.
TL;DR: Feed any invertebrate to your mantis as long as it's not toxic or warned against. Green inverts and moths are nearly always preferred. Mantids will take nearly anything with adequate coaxing, however remember that mantises vary greatly in terms of enthusiasm over food and physique.
