(Fig. 1 A)
Diagnosis. This species belongs to the Aprionus flavidus (Winnertz) group of species, whose members are characterized by the gonostylus subdivided in two lobe-like portions, the ventrobasal portion is thick and convex, the dorsoapical portion is more narrow and elongate. Between both portions are 1–2 spines of varying size and shape (Jaschhof & Jaschhof 2009). In A. forshagei, the gonostylus has 1 straight, blunt-ended spine (↓) situated between two lobe-like portions subequal in size; the dorsoapical portion bears 1 slightly bent apical spine and 2–3 subapical bristles. The tegmen is long, narrow and tapered apically; the apex is covered with tiny spikes (↓); tegmen fingers, arranged in 1–2 pairs, are small and inconspicuous. The subanal plate is largely membranous and can be perceived only because its posterior margin and anterolateral edges are slightly sclerotized (darkened).
Aprionus delectabilis Mamaev (Jaschhof & Jaschhof 2009: fig. 78) and A. hybridus Jaschhof (Jaschhof & Jaschhof 2009: fig. 81) have genital structures similar to A. forshagei, but the gonostylus, tegmen and subanal plate are distinct in each of these three species.
Other male characters. Body size 1.1 mm. Head. Eye bridge 2–3 ommatidia long. Postocular bristles 6, in 1 sparse row. Neck of fourth flagellomere shorter than node; node with 1 complete and 3 incomplete crenulate whorls of sensory hairs, about 4 thick hair-shaped translucent sensilla distally. Maxillary palpus 3 -segmented; first segment with hair-shaped translucent sensilla; apical segment longest. Wing. Apical portion of R 1 twice as long as Rs. Legs. Claws thin, evenly slightly curved, without teeth. Terminalia (Fig. 1 A). Ninth tergite subrectangular, with concave, reinforced anterior margin. Gonocoxa rounded posteriorly; dorsal gonocoxal bridge extending far anteriorly.
Etymology. This species is named after Mattias Forshage, Stockholm.
Holotype. Male (CEC 76), Sweden, Östergötland, Ödeshög, Omberg, Storpissan Nature Reserve, old-growth Norway spruce forest, 18 June– 20 July 2009, Malaise trap, M. & C. Jaschhof (in NHRS).