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I'm happy that i could find it for you. I hope that it is useful to you.

I don't think that the causes are unknown so much as noone wants to use science to deduce the cause. Remember when science required the path of hypothesis, theory, then law? today we seem to be publishing theories. I think that biochemistry could tell us the cause but noone is investigating this. missing ovaries indicates missing chemical or hormone (if this is appropriate for diptera.) I think that the world is lacking biochemists or noone is interested in this particular study. I suppose that if it isn't related to agriculture, weaponry or technology, then funding is not available?

anyway, i'm sure that a scientific answer can be found but we need more scientific people to participate. I wish i were better at math and chemistry. I wish i were a millionaire, then i could spend some time studying alot of things.