The flies can also be conditioned by electric-shock treatment to exhibit aversion to either form of the molecule, and the researchers say that shows they can clearly distinguish between them.
Critical of the idea? Co-authors Luca Turin of MIT addresses some of it in the comments on the Nature News piece by Philip Ball.
Citation: Franco, M. I., Turin, L., Mershin, A.&Skoulakis, E. M. C. Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1012293108 (2011)