I'm not a lot interested in fruit flies, as such, but they (Drosophila) have been a great deal helpful to science in general and especially in the genetics corner.
It seems that female fruit flies are fussy. After the first time they have intercourse, they don't want to do it again.
Someone has discovered (or thinks he has) how.
Now this is how you find out the the details of the complicated and devious mind of the female fruit fly.
You feed them. With yeast that contains lots of heavy nitrogen. That isotope labels all of the female proteins.
Then you look at them after they've fucked. Anything that didn't have the heavy nitrogen was given by males. The researchers discovered some sixty-three proteins from fruit fly semen, which may suggest that the male fruit fly lacks confidence in his wife's fidelity, and is over-doing it a bit.
(Sorry to anyone who's offended by the fffour-letter word - the alliteration was just too good to resist).