HYMENOPTERA 



923 



other Hymenoptera in having the narrow cell just behind the costal 

 vein obliterated by the fusion or close approximation of the costal 

 vein and the vein behind it and usually by having some of the ab- 

 dominal sterna membranous. They differ from braconids in having 

 cells Ml and ist M2 of 

 the fore wing separ- 

 ated by a vein (Fig. 

 1 152) and the second 

 and third abdominal 

 tergites movable. 

 There are a very few 

 exceptions to one or 

 the other of these char- 

 acters. Except for the 

 frequent absence of 

 the areolet, a small cell 

 near the middle of the 

 wing (Fig. 1 152), ich- 

 neumonids have a very 



constant and distinctive venation in the fore wing. Many species 

 are wasp-like in appearance but may at once be recognized as ich- 

 neumonids by the long many-segmented antenna. 



Except perhaps for the Chalcididae this is the largest family of the 

 Hymenoptera. Probably about six thousand species occur in the 

 United States. All are parasitic and many are important enemies of 

 destructive insects. The taxonomy of the family is difficult because 

 the subfamilies and tribes are not easily characterized and must be 

 learned by experience. Five subfamilies are usually recognized, but 

 these are admittedly unnatural in some degree and any definition 

 of them is subject to exceptions. The student, however, can place 

 most of the common species by means of the key below. Some of the 

 more important tribes of ichneumon flies are discussed under the 

 different subfamilies, but space will not permit all of them to be 

 mentioned. 



Fig. 1 1 52. — Wings of an Ichneumon fly. 



Tribes of Pimplinae, Proc. U. S. Nat. Mus. 1921, vol. 60, art. 4, pages 1-7; Labe- 

 nini, Rhyssini, Xoridini, Odontomerini, and Phytodietus, Proc. U. S. Nat. Mtis. 

 1920, 57 : 405-474; Acoenitini, Proc. U. S. Nat. Mus. 1920, 57 : 502-523; Ly- 

 corini, Polysphinctini, and Theronia, Proc. U. S. Nat. Mus. 1920, 58 : 7-48; 

 Pimplini (except Theronia), Proc. U. S. Nat. Mus. 1920, 58 : 327-362; Odon- 

 tomerus, Proc. U. S. Nat. Mus. 1930, vol. 77, art. 3, 15 pages; Cremastini, Proc. 

 U. S. Nat. Mus. 1917, 53 : 503-551 and Proc. U. S. Nat. Mus. 1920, 58 : 268-288; 

 Cryptini with a very small areolet, Proc. U. S. Nat. Mus. 1929, vol. 74, art. 16, 

 58 pages; Exetastes, Proc. U. S. Nat. Mus. 1937, 84 : 243-312; Netelia, Lloydia 

 1938 (1939), I : 168-231; Trogini, Trans. Amer. Ent. Soc. 1939, 65 1307-346; 

 Ichneumoninae, Travis. Amer. Ent. Soc. 1877, 6 : 129-212; Diplazonini, Trans. 

 Amer. Ent. Soc. 1895, 22 : 17-30; Tryphoninse (except Diplazonini), Trans. Amer. 

 Ent. Soc. 1897, 24 : 193-348; Glypta and Lissonota (= " Lampronota"), Trans. 

 Amer. Ent. Soc. 1870, 3 : 151-166. The last four papers cited are out of date and 

 somewhat unreliable, but are the best available. Ashmead ('00) has given a key 

 to all the genera, but the student will find this unreliable. 



