During a laboratory biological study of a midge, Feltiella acarisuga (Vallot, 1827) (Diptera: Cecidomyiidae), acarivorous on two-spotted spider mites, some ceraphronid specimens were reared from the midge cocoons. A detailed morphological study and comparison with previously known species revealed that the ceraphronid is a new species of Aphanogmus Thomson, 1858 (Hymenoptera: Ceraphronidae). The new species is described as A. feltiellophagus Lotfalizadeh, sp. nov. and compared with closely related species. An identification key for all Aphanogmus species associated with predatory cecidomyiids is provided. As a parasitoid of the pupal stage of Feltiella acarisuga, the potential negative impact of A. feltiellophagus on the biological control of tetranychid mites is discussed.