I am a hybrid breeder (guppys X mollies)for a local pet store, I just can't figure this one out. I buy usually ribbon red tail, green cobra and blue dragon guppies, endler's for my base stock. what I am have trouble with is that all my male guppies keep dying I am not sure why, the only thing that are surviving are my male black mollies. My hybrid babes are surviving, I have over 67 fry in one tank, of my "black widow guppies" solid black with large red paddle tail.
The Mollies aren't attaching anyone (that I know of) and the water is excellent, and I am constantly replenishing my stock.

Does anyone have ideas?

go to aqadvisor.com to check your stock to see if your tank is for sure not overstock

If the water parameters are good then over crowding seems unlikely but you always would have the potential for stress due to over crowding even if the water tests good.

Of the fish that die are there any signs of illness? Do you always restock from the same supplier?

It could just be that the place you are buying from has a bad supply of fish at the moment compared to the past.

Has anything changed in the way your tank is setup? Filtering? temp? water changes? Think of anything you might of changed no matter how small when these problems first started happening.

I've recently had an aquatics LFS manager confide in me that she wishes they'd quit purchasing certain guppy types in. Apparently, they're being over-produced and inbred to the point that there is a very high mortality rate.

You might try a different type or supplier. Could be inbreeding depression making them weak.