Cool !
Je vois 
ICI que 
Phimenes flavopictum (qui semble bien correspondre à "mon" exemplaire) est synonyme de Delta arcuata ...
Et je lis 
ici que :
"The members of this genus [
Delta] are distinguished from those of related genera such as 
Phimenes Giordani Soika and Oreumenoides Giordani Soika 
by the short length of second metasomal tergum, less than 1.25 times the length of its mesosoma and male antenna hooked apically. 
Research paper: Taxonomic Notes on the Genus Delta de Saussure (Hymenoptera: Vespidae: Eumeninae) from Vietnam. Available from: 
https://www.researchgate.net/publicatio ... om_Vietnam [accessed Apr 9, 2017]."
Et 
là, encore, page 38 je trouve cette clé :
"Keys to the genera of Eumeninae
1. Propodeal valvula elongate, rectangular; submarginal carina produced; second
submarginal cell forming obtuse angle basally …………………………………. 2
- Propodeal valvula short, rounded; submarginal carina not projecting; second
submarginal cell acute basally ………………………………………………….. 3
2. 
Metanotum dentiform mesally; 
tegula equalling, not exceeding 
parategula
posteriorly; female with 
fovea anterior to mid-ocellus; metasomal petiole
abruptly swollen apically; Mesepisternum with epicnemial carina present
………………………………….……………………….….... Labus de Saussure
3. Mesepisternum with epicnemial carina present; TII 
apical lamella strongly and
broadly concave medially .................................................................................... 4
- 
Metanotum not dentiform; 
tegula exceeding 
parategula posteriorly; female
without 
fovea on 
vertex; metasomal petiole not conspicuously swollen;
Mesepisternum with epicnemial carina absent ……..………………..……
……………...……………………………………….…...…... Eumenes Latreille
4. TI with section after 
spiracles shorter than section before 
spiracles
……………………………………………………………..… Delta de Saussure
- TI with section after 
spiracles longer than section before 
spiracles ………..…. 5
5. 
Pronotal carina absent medially; male antenna hooked apically ……………
…………………………………………………..…… Phimenes Giordani Soika"
Pas certain que l'on voit les éléments sur ma photo ...