The differences are slight in the male genitalia between hostilis and adelphella. The valva shape differs with the thickening in adelphella being more curved. The juxta are different shapes. The uncus is wider/more parallell sided in adelphella. The thickening in the duct of the aedeagus is more developed in adelphella. The part of the aedeagus with many small spines is well developed in hostilis.
Colin Plant says: "Amongst the alleged British taxa, only nigricans and eruta have the long whiskers emanating from the region of the apophyses posteriores"