8o 4 M. W. R. de V. GRAHAM 



Biology. The list of hosts in North America given by Peck (1963) includes 



species of Diprion and Neodiprion (Hym., Diprionidae) ; Pristiphora erichsonii 



(Htg.) (Tenthredinidae) ; and Mesoleius tenthredinis Morley (Ichneumonidae). 

 Imagines June-July. 



DIBRACHYS Forster 



Dibrachys Forster, 1856 : 65. Type-species : Pteromalus boucheanus Ratzburg, by designation 



of Thomson, 1878 : 47. 

 Pteromalus sgen. Dibrachys Forster ; Thomson, 1878 : 147, 160-162. 

 Dibrachys Forster ; Ashmead, 1904 : 320, 322. 



Dibrachys Forster ; Schmiedeknecht, 1909 : 329, 330, 358, [ex parte]. 

 Dibrachys Forster ; Kurdjumov, 1913 : 11-12. 

 Coelopisthoidea Gahan, 1913 : 179. Type-species : C. cladiae Gahan, by original designation. 



Dibrachys Forster 

 Dibrachys Forster 

 Dibrachys Forster 

 Dibrachys Forster 



Gahan, 1938 : 211-213. 

 Nikol'skaya, 1952 : 218-219. 

 Peck, 1963 : 674-683. 

 Boucek, 1965^ : 28-30. 



The genus was erected by Forster (1856 : 65) without included species. The 

 type-species is Pteromalus boucheanus Ratzeburg (1844a : 196), according to Gahan 

 & Fagan (1923 : 43) who stated that it was designated as such by Thomson 

 (1878 : 47). Thomson's statement occurs in a Swedish footnote referring to the 

 genus Colotrechnus, and may be translated as follows : " Note. Dibrachys Foerster 

 would agree best with this genus [i.e., with Colotrechnus] but Reinhard has sent me 

 Pteromalus Boucheanus as type for that genus " [Dibrachys] . Farther on in the 

 same volume (loc. cit. : 161-2) Thomson included two species in Dibrachys, viz. 

 boucheanus (Ratzeburg) and acutus Thomson. It seems clear that Thomson 

 accepted Reinhard's selection of boucheanus as the type-species. 



Reinhard's interpretation of Dibrachys has been accepted by all authors subsequent 

 to Thomson, and there would be no point in attempting to alter it. It is interesting 

 to note, however, that Thomson, with his remarkable insight, was evidently right 

 in his surmise that Forster's concept of Dibrachys really referred to the genus now 

 known as Colotrechnus Thomson, because Dr. Novitzky wrote to me some years ago 

 " Forster created Dibrachys for an undescribed species, remains of which in the 

 Vienna Museum are clearly a species of Colotrechnus ". 



The type-species of Dibrachys (boucheanus Ratzeburg) has hitherto been only 

 subjectively defined ; the type material appears to have been destroyed in 1945 

 together with most of Ratzeburg's collection, hence no lectotype can be selected. 

 However, Thomson (1878 : 161) cited Pteromalus cavus Walker (1835 : 477) as a 

 probable synonym of boucheanus, and his view has gained general acceptance (for 

 an extensive list of references to cavus and boucheanus see Peck, 1963). As cavus 

 Walker is the earlier name, and the species is represented by several original 

 specimens in Walker's collection, it can be objectively defined by selecting a lecto- 

 type, and one is designated in the present paper. Failing the discovery of original 

 material of boucheanus, the lectotype of cavus might conveniently be made neotype 



