Hey all, firstly nice site and forum!
Anyway, here's my input. I don't think temperature has anything to do with the sex ratio of hatchlings, but i could be wrong. The structure of the ootheca and the foam itself helps maintain a microclimate within the ootheca to ensure the optimum environment for oocytes development. For example, Gongylus ootheca are ribbed shaped to prevent the ootheca from overheating. When you slice open an ootheca (phyllocrania in this case), you can see each oocytes are placed into its own little "cell" (and not in a random order). So the ootheca foam and the positioning of the oocytes are most likely to be linked to some sort of regulation to ensure the optimum conditions for oocyte development. Otherwise, why would the female waste so much energy into producing ootheca instead of laying their eggs directly on twigs. Although the hard protecting coating of the ootheca is also used to protect the oocytes from parasitic wasps. I don't think there are any predators that solely eats mantids oothecae. So apart from protection, the ootheca must be used for some sort of internal environment regulation (most probably thermoregulation). So the internal temperature must be more or less constant. Unlike reptiles, one egg may be laid in a slightly hotter environment so therefore producing a male while another egg may be laid in a cooler environment therefore producing a female.
Sorry for going off the tangent abit.
Chun