Key to the known last instar larvae of Hexatoma of Mongolia

1. Apex of ventral lobes of spiracular disc with cluster of similar length hairs, but lacking several much longer setae (Fig. 26). Maxillary palpus as long as mandible (Fig. 21). Last instar larvae large, more than 30 mm long.................................................................................. Hexatoma (Eriocera) sachalinensis (Alexander, 1924)

- Apex of ventral lobes of spiracular disc with cluster of similar length hairs, and several much longer setae (Fig. 33, 44). Maxillary palpus almost twice as long as mandible (Fig. 1). Last instar larvae about 20 mm long.......................... 2

2. Marginal hairs on the tips of lobes dark brown, in other parts light brown. Each ventral lobe of the spiracular field covered with a wide “Y” shaped sclerite, the dorsal inner branch fused with its opposing sclerite (Fig. 44)........................................................................................ Hexatoma (Eriocera) ussuriensis Alexander, 1934

- All marginal hairs of spiracular lobes light brown. Each ventral lobe of the spiracular field covered with a wide “Y” shaped sclerite, completely separate from its opposing sclerite (Fig. 33, 57) .............................................. 3

3. “Y” shaped sclerite of each ventral spiracular lobe with widest part no wider than sclerite of lateral lobe............................................................................. Hexatoma (Eriocera) stackelbergi Alexander, 1933

- “Y” shaped sclerite of each ventral spiracular lobe with widest part over twice as wide as sclerite of lateral lobe.................................................................... Hexatoma (Hexatoma) nubeculosa (Burmeister, 1829)