An entomologist who specializes in the order Diptera (true flies).
1857, Henry Tibbats Stainton (editor), Review of Francis Walker, Insecta Britannica - Diptera, Volume 3, in The Entomologist's Annual, page 170,
It must be very gratifying to Mr. Walker to hear the dictum of the great Dipterist of Posen, Professor Loew, that the arrangement “adopted by Mr. Walker is one of the best, or even the best, systematic arrangement of the Diptera that has yet been proposed."