No, I do not know. I have not seen the holotype of D. langsonius Fairm. . Here the original description : 63.75 KB
I have many specimens from Laos and some from Taiwan : some of them have 2 black spots on pronotum (never easy to see), and most of them not. All specimens have spine on 3rd and 4th antennomera. I do not see any difference with Gressitt holotype from Bishop Museum (D. alboantennatus). It could be a synonym, but without seeing holotype of Fairmaire species...
Laos: Demonax reticollis
Posted - 23/11/2015 : 18:54:06
