My bonus dad was a tsetse fly sexer in Northern Rhodesia. Not sure how you sex tsetse flies, because kittens are bad enough.
When I worked in rescue, we learned the ‘dots’ version that is that : was a male and i was a girl. But it is still pretty hard. I had a student whose ‘male’ rescue cat had kittens on the carpet while we were having a lesson (they did not know how old ‘he’ was when he was rescued because he was very small, so were waiting 6 weeks to sterilise)
This is a nice downloadable version also from the same site (credited in image and PDF)