My brother and I have a Devils flower mantis and I can't tell whether it is a male or female. I think it is about L7 or L6 right now. Could you tell the genders at that stage?
You should be able to tell now. there is an idolo article pinned, In this forum. It should answer any gender questions. If you still can't tell, a picture would allow us to tell.
I was able to sex mine at their second instar. you're looking for the presence of a smaller, extra exoskeletal protrusion on the underside of the abdomen near the end that the females lack. The females have just the three large protrusions and the male has three large ones plus one small one on the segment after. Just don't get fooled into thinking the tip of the subgenital plate on the female is an additional protrusion--you'll be able to tell because the subgenital plate will cover the segments that will become parts of the ovipositor on the female and you'll see the additional segments on the male.