The female and male of a new species, Brachytydeus elongatus sp. nov., are described from leaves of common reed (Phragmites australis) in Tyumen Oblast of Russia. Brachytydeus obnoxius (Kuznetsov and Zapletina) is recorded from Russia for the first time; B. inconstans (Kazmierski) and B. ferulus (Baker) are recorded from Western Siberia for the first time. An unusual type of secondary sexual dimorphism in Brachytydeus elongatus sp. nov. is discussed.