ICHNEUMON-FLIES, PART 2\ EPHIALTINAE 209 



14. Genus Perithous 



Figure 292, a 



Perithous Holmgren, 1859, Ofvers. Svenska Vetensk.-Akad. Forh., vol. 16, p. 123. 

 Type: Ephialtes albicinctus Gravenhorst; designated by Viereck, 1914. 



Front wing 6 to 13 mm. long; body long and slender; face, frontal 

 orbits, and clypeus white or partly white; clypeus usually convex 

 basally, its apical 0.6 ± flat or a little concave, its apical margin with a 

 deep median notch; occipital carina complete, without a median dip 

 above; hairs on mesoscutum moderately dense, evenly distributed; 

 submetapleural carina complete; propodeum rather short and strongly 

 convex, without median longitudinal carinae, its petiolar area large, 

 often completely bounded by a carina; areolet roughly an equilateral 

 triangle, receiving second recurrent vein basad of its apical corner; 

 nervellus broken at or above the middle; tarsal claws of female without 

 a basal tooth (with a large basal tooth in all other Nearctic Pimplini); 

 first tergite moderately long, its basolateral angle prominent, its 

 lateral longitudinal carina very strong, its median longitudinal carinae 

 distinct only at base; second tergite with short, transverse, basolateral 

 grooves and more distinct apicolateral oblique grooves; third and 

 fourth tergites with moderately developed tubercles, their apical im- 

 punctate margin indistinct, occupying about 0.1 their length; female 

 subgenital plate sclerotized laterally and apically, the rest mem- 

 branous; ovipositor compressed, weakly upcurved, its apex as in 

 figures 331,e,f, or in an Old World subgenus the apex sinuate and with 

 a different arrangement of teeth; ovipositor sheath 0.9 to 1.8 as long 

 as front wing. 



This genus occurs mostly in the Palaearctic and Oriental regions. 

 There are only two species in our fauna, one of which was introduced 

 from Europe and the other a naturally Holarctic species represented 

 in North America by two subspecies. The species parasitize the 

 nests of aculeate Hymenoptera in canes and twigs. Our two species 

 have a bright distinctive coloration, the abdomen being narrowly 

 banded with white and the thorax largely ferruginous. Among the 

 Nearctic Ephialtinae, only Tromatobia zonata has a similar coloration. 



Key to the Nearctic Species of Perithous 



MALES 



1. Second tergite about 1.5 as long as wide (but this proportion unusually vari- 

 able) ; hind tibia and tarsus usually with strongly contrasting fuscous and 

 white markings; mesoscutum varying from ferruginous with only the lateral 



edges black to entirely black 1. mediator (Fabricius) 



Second tergite about 1.1 as long as wide; hind tibia and tarsus with weakly 

 contrasting brown and stramineous markings; mesoscutum ferruginous with 

 only the lateral edges black 2. divinator (Rossi) 



