ATTENTION : This key treat only of Genera having at least one species which the length of forewing is ≥ 6.0 mmHowever I added the species having a length of forewing slightly lower than 6.0 mm
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Biblio. - 
Diller 1969 : Beitrag zur Taxonomie der Gattung Syrphoctonus ...
in "Acta Entomologica Musei Nationalis Pragae - 38 p.545/552"
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Diller 1982 : Untersuchungen über Arten der Gattungen Diplazon Viereck, 1914, und Sussaba Cameron P., 1909 ...
in "Entomofauna - 3(6) p.65/79"
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Fitton & Rotheray 1982 : A key to the European genera of Diplazontine ...
in "Systematic Entomology - 7(3) p.311/320"
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Klopfstein 2014 : Revision of the Western Palaearctic Diplazontinae ... "Zootaxa - 3801"
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Townes 1969/1971 : The Genera of Ichneumonidae - Part 1 & 4                                  
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See also my diverse Messages titled :
"Adaptation for the ♂ & ♀ (of France and Italy) of the subFamilies's Key ..." 
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The Genera are 
sensu Townes -----
Tergites's Drawings of 
Diplazon & 
Enizemum from 
Townes -----------------------------------------keywords :
Hymenoptera Ichneumonidae Bioblapsis polita Campocraspedon caudatus  Promethes nigriventris Sussaba punctiventris Diplazon pectatorius laetatorius Syrphoctonus tricinctorius Enizemum schwarzi ornatum nigricorne Syrphophilus tricinctorius Homotropus crassicornis dimidiatus strigator frontorius