ICHNEUMON-FLIES, PART 2 1 EPHIALTINAE 175 



or pale yellow except in T. variabilis; clypeus convex, its apex a 

 little impressed, its apical margin weakly concave or approximately 

 truncate; occipital carina complete, not dipped on the midline; 

 mesoscutum with moderately dense, evenly distributed hairs or in 

 some Neotropic species with sparse hairs and some bare areas; sub- 

 metapleural carina complete, partly absent, or represented only by 

 a tubercle behind middle coxa; propodeum rather short and convex, 

 with or without median longitudinal carinae; areolet sub triangular, 

 absent, or in T. variabilis subpentagonal, receiving second recurrent 

 vein before its outer corner; nervellus broken at or above the middle, 

 first tergite short, broad, its lateral and median longitudinal carinae 

 rather strong; second tergite with weak, basolateral oblique grooves; 

 third and fourth tergites with distinct tubercles, then* apical impunc- 

 tate band occupying about 0.15 their length; female subgenital plate 

 completely sclerotized or with a median basal membranous area that 

 varies from small to so large that it occupies most of the area of the 

 sternum; ovipositor compressed, straight, its lower valve with a 

 weakly wrinkled surface, its point as in figure 331, c; ovipositor 

 sheath 0.35 to 0.60 as long as front wing. 



This genus is Holarctic and Neotropic. There are four Nearctic 

 species. 



All species of the genus are gregarious parasites of spider egg 

 cocoons. It is common to open a large egg cocoon of an orb weaver 

 spider and find several Tromatobia larvae or cocoons and most or all 

 of the spider eggs destroyed. The biology, larva, and pupa of the 

 European T. oculatoria was described in detail by Nielsen (1923, 

 Entomologiske Meddelelser, vol. 14, pp. 189-194). There have been 

 no similar publications on the Nearctic species. 



Key to the Nearctic species of Tromatobia 



1. Frons entirely black; propodeum with a prominent sublateral longitudinal 



ridge; face of male black; hind tibia ferruginous with dusky subbasal and 

 and apical bands (fig. 322, a). Variabilis group (p. 176). 



1. variabilis (Holmgren) 

 Frons white next to eye, at least in part; propodeum without a distinct sub- 

 lateral longitudinal ridge; face of male white 2 



2. Carina between metapleurum and metasternum (submetapleural carina) 



present only basally, not complete to hind coxa. Notator group (p. 186) 

 The only Nearctic representative of this group has the thorax entirely 



fulvous 4. notator (Fabricius) 



Carina between metapleurum and metasternum (submetapleural carina) com- 

 plete, extending from in front of hind coxa to front of metapleurum; thorax 

 usually largely or entirely black. Oculatoria group (p. 178) 3 



3. Tergites 1-5, or 2-5 with a white preapical band; areolet absent. 



3. zonata (Davis) 

 Tergites 1 to 5 without a white band; areolet present . . 2. ovivora (Boheman) 



