I have a BIG question on hybridization. Is it the physical shape of the genitalia that prevents roaches of different species from hybridizing, or is it their genetics?

Both, but closely related species may still hybridize.

do tell any specifics, or examples. ???

From what I've heard "Princisia sp." readily hybridize with Gromphadorhina, and then there's the whole Blaberus mess...

Sure, as mentioned the various Gromphadorhina species and so-called "Princisia" cross readily in captivity because they have the same male genitalia. The species designations are based on pronotum structure, granulation and setae which vary by population. The question is are any of the species really valid or are they mostly valid but readily hybridize (the genus "Princisia" cannot be valid when even the species are difficult to prove). G. oblongonota and "Princisia" have readily crossed in captivity (like G. portentosa and "Princisia") and it's very likely G. oblongonota and G. portentosa cross just as easily. Hopefully hobbyists will be careful about not crossing these, or at least labeling crosses, or we'll just end up with one big messy population that loses the uniqueness of its geographic varieties.

thanks for the feed back on the hisser hybrids, as i might have had some originally, as some looked odd from types, but now this last generation killed off the last of the odd ones, and only a few look differant from the crowd. i was wondering manly about the blaberus species, but cant find any of the odd ones now, so must have fed all the what now know were B. cranifer black wing, and some other kind off by mistake, or the dubias ate them. lol

Once there has been hybridization in the colony, that’s it. You can’t just pick out the hybrids. Once the bloodline has been tainted EVERY SINGLE offspring is a hybrid whether they resemble one or look pure. Even if you take a hybrid and breed it out to a pure individual and keep breeding the offspring back to a pure strain… it’s still a hybrid. At that point there is only one way to get a pure culture, feed every individual off to your Theraphosa blondi and start up a brand spanking new culture.

thanks, i wasnt thinking the cranifer wound be a problem to the dubias though, and the hissers ate all the odd balls off before they matured (are some kinds just more aggressive than others?). i originally thought i had some odd ones, but after reading, seems they were just mutations that are normal, besides the ones that were cranifer mating together. i havent seen any babies in my hissers, and been looking for undesirables in my dubias and not finding any besides the pink and yellow ones occasionally(are there anything i would have to worry aabout whith the dubias?). with most cultures coming from over seas, and so much confusion on names and such, is there any differance or way to tell for sure what one has if they look like a pure strain? like many of the small pythons( like carpets), and leopard geckos were interbred at first because of not knowing that there were differances, or for the sake of getting the look, but wanting the captive feeding responce that the look wanted didnt do in captivity.