I believe it would be one before the molt even. All common mantises with the exception of monogamous spearers are highly territorial. About a 50-75 gallon tank could hold a couple of N. wennerae (only about 3" tops) safely, so I think you get the idea. Besides peacocks don't become sexually mature until after 3" and any coupling would be for a short while (couple of weeks). The larvae of most stomatopods are incredibly difficult to raise, doubly so with Odontodactylids, many of which have a 4 month+ planktonic state. Also mantises have good memory and could only mate with the same mantis mayube 1-2 times a year. They are reluctant to mate with the same one more than once-at least thats what I've read from Dr. Roy, but that may not be completely right
Dan