It is a well known fact that at least in some reptile sp., crocodilians and chelonians, for example, sex of the hatchlings is at least to some degree determined by the incubation temps. Does this occur in roaches? I ask because my adult B. craniifer appear to be all female. James T. told me how easy it was to sex them and when I checked about 12 random adults the last segments all look the same. When I look at my other Blaberus sp., either adults or large nymphs, I can see the distinction easily. I've also seen several posts on this forum with great pics. The friend that I got these from gave me about thirty adults and they all look the same. He keeps his culture in a glass tank on the floor of his reptile/roach room. The room temp is held right around 78-80 all the time, but I'm guessing its a bit cooler down there on the concrete floor. I'll take my temp gun and get an accurate temperature reading from the floor where he keeps them the next time I'm over there. My roach room fluctuates between 80 on a cold night and 90 during a hot day and I keep them in tubs on a shelf about 4 feet off the ground. I've got quite a few babies and nymphs now, so as they mature I'll keep an eye on how they develop. Thanks for any insight into this.

Hmm... I don't know. I keep my B. craniifer in the high mid-70s, and I seem to have quite a few males (I don't check every single one of them, though.) I believe it's more genetically influenced (I'd assume some species like those from Polyphagidae, particularly desert species, would have higher male-to-female ratios.)

No, sex determination comes from females possessing XX chromosomes and males with one X (shown as XO with O being no chromosome).

Yay clarification!

Thanks for the reply. I don't see how this means incubation temps. don't affect the sex. In the previously mentioned animals the fertilization and xx/xy business is all done before the egg is shelled and then laid. But somehow, unusually high or low incubation temps. "create" either more males or more females. It seems like a fairly similar process is taking place in our roaches. I'd love to learn more about this.

Actually if remember back to herpetology correctly, crocs and the like don’t have the sex chromosomes like humans (X and Y) do. The gender is determined by the environments affects on which genes are being expressed (utilized). In other words, you couldn’t just take genes out of the animal and look at the gender; they are all both genders genetically speaking. So in cockroaches, after fertilization (if there is fertilization) sex is what it is. I can’t make sense of how the genetics would play out if you were genetically one sex and phenotypically the other… it doesn’t make sense. The odd sex ratios could be explained in other ways however, not just temperature dependency.

Hi

BugmanPrice is absolutely right!
In reptiles sex is either determined by chromosoms OR temperature (and maybe other environment factors). All reptilian species so far examined have either contain sex chromosoms (or microchromosoms in case of for example Pogona vitticeps) and aren't influenced by temperature or they have no sex chromosoms and sex develops during incubation of the eggs. (See Wikipedia for overwiev: CLICK)
There were done some experiments with P. vitticeps (publications online available ) showing that very high temperatures "produce" mainly male offspring (and kills a good percentage of the eggs) which are male or female by chromosoms! The good/bad thing explaining why this works is, that the genetically female males ('pseudo-males') are sterile! It seems that this lizzard once had a temperature dependent sex determination which under extreme conditions still works and dominates the sex chromosoms. Very low temperatures seem to result in more female than male offspring because males are more sensitive and just die earlyer (and at such low temperatures the death rate is very high).

If I have it correctly in mind: In one publication they raised the question about what could be in between because there seem to be reptiles which have lost chromosome determined sex determination and others which gained it late in evolution (due to examinations on closely related species). It would be amazing if the transition were sharp (switch off environment/temperature sensing pathways and 'create' a sex chromosome or vice versa). Evolution usually goes gradually if there is no 'jump' caused by a single mutation (or you read the 'evolution v.s. creation poll' ).

Grüessli
Andreas

Okay. Good info all. Back to the original question. How do I have all females? These roaches were kept significantly cooler than than most people keep them. Might this somehow be a factor? I certainly can't explain it. We just grabbed 20 random roaches out of his culture. The were all running all over the place so we just grabbed whatever we could catch.

Maybe the females ones are slower and easier to catch! You could always post up some pictures of the last segment to be sure...

I've kept B. craniifer at 67-72F and the gender ratio was still approximately 50/50. Of course they didn't breed very well.