Proc. R. Soc. B doi:10.1098/rspb.2010.1390 (2010)

Female fruitflies are known to shun repeated sexual encounters when nutrients are scarce, a probable adaptation to a meagre environment in which offspring are less likely to survive. Signalling in the nutrient-sensing insulin pathway may underlie this behaviour, say Stuart Wigby, now at the University of Oxford, UK, and his colleagues.

The researchers deleted key genes in this pathway in virgin fruitflies and noted that, initially, the flies did not hesitate to mate with normal males. A day later, however, they displayed much less interest in a second round of mating than did normal flies of similar body size and fertility.