Diagnostic description.

Female. Body size 6.8 (6.4–6.8) mm, ovipositor length 4.8 (4.3-5.3) mm, fore wing length 5.1 (4.6–5.1) mm (Fig. 73A); colouration black, except scape, pedicel fore and mid legs pale brown (coxae dark brown), hind legs dark brown except tarsomere 1 spex, 2–4 cream-coloured, Ovipositor sheath dark brown, wings hyaline except for indistinct brown infuscation at apex 1st marginal and 4th submarginal cell (Fig. 74G), hind wing veins spectral; head shape quadrate, width 1.3 (1.1)) × length, postocular space 0.6 (0.6) × eye length in dorsal view (Fig. 74C), raised transverse carina above toruli absent, malar space 0.1 (0.1–0.2) × height of eye (Fig. 74A); occipital carina present laterally becoming absent medially; length of scape 1.3 (1.3–1.4) × length of pedicel, 1st flagellomere 1.4 (1.0–1.3) × length of scape, 0.6 (0.6) × 2nd flagellomere; mesosoma length 1.6 (1.6–1.7) × height, mesoscutum in lateral view rounded antero-dorsally (Fig. 74D); mesoscutum length 1.0 (1.0) × width in dorsal view (Fig. 74E); medial lobe rugose; ovipositor guide oblique, positioned medially, ventral lobe acute (Fig. 74F); ovipositor sheath length 0.9 (0.9) × fore wing length (Fig. 73A); 2-Rs+M 1.2 (1.2) × 1-Rs+M, three hamuli, equidistant (Fig. 74G); metasoma clavate,T1+T2 length 3.0 (3.0–3.8) × width in dorsal view.

Males. Body size (6.2–9.7) mm, same as female (Fig. 73B).

Although Aulacus rieki is superficially similar to Aulacus bamagensis in general appearance, they can be easily separated on the shape of the head in dorsal view, quadrate (conical in A. rieki), and coloration of metasoma without orange colouration (metasomal T2–T3 orange in A. bamagensis).