HYMENOPTERA 919 



parasitoid for the economy of the parasitic Hymenoptera (see Wheeler 

 (23), page 26), for although the host is kept alive and usually de- 

 veloping while it is being consumed the parasite eventually devours its 

 prey completely as does a true predator. With the infinite variation 

 in types of parasitism and the frequent intergradation with other modes 

 of life it seems useless to try to restrict the term "parasite " too closely. 



Adult ichneumonoids feed upon the honey-dew secreted by 

 Homoptera and at flowers such as Umbelliferae whose nectar can be 

 reached by the insect's usually short mouth parts. For water, of 

 which they need a good supply, they lap up dew or rain drops from 

 leaves. The females frequently feed upon the host juices that exude 

 from punctures made by the ovipositor. Some species will attack a 

 larva or a pupa just for this purpose, puncturing it again and again to 

 lap up the juices, but never depositing an egg. Since only the larva 

 is parasitic, adult ichneumonoids show none of the degenerative 

 specializations for a parasitic habit that would otherwise be expected. 



Polyembryony, or the development of several larvse from a single 

 egg, is known to occur among the ichneumonoids only in the braconid 

 genus Macrocentrus. Parthenogenesis is possible in most species. 

 Unmated females usually produce only males. In a few cases females 

 are produced. In these species the male is usually either extremely 

 rare or entirely unknown. 



Family STEPHANID^ 

 The Stephanids 



The stephanids are among the strangest of the Hymenoptera. 

 The spherical head is on a long neck and has a crown of teeth. The 

 very slender antennse arise just above the mouth. The hind femur 

 is enlarged and has a series of teeth beneath. These insects are rare 

 outside of the tropics and even there are not common. Their life 

 history is unknown although they are supposed to be parasitic on the 

 larvae of wood-boring beetles or in the nests of solitary bees or wasps. 



Family BRACONID^* 



The Braconids 



The Braconidas have a close superficial resemblance to the Ich- 

 neumonidas. They differ from this family in always lacking vein M2 

 so that cells Mi and ist M2 are confluent (Fig. 11 48) and, except in 

 the subfamilies Aphidiinae and Paxylommatinas, in having the second 



*Ashmead ('00) has given a key to the genera of Braconidae, but unfortunately 

 this is difficult to use and contains many errors. Some recent revisions of North 

 American species and genera are as follows: Aphidiinee, Bull. Md. Agr. Exp. Sta. 

 191 1, 152 : 147-200; Opiinee, Proc. U. S. Nat. Mus. 1915, 49 : 63-95; Bracon, 

 Proc. U. S. Nal. Mus. 1917, 52 : 305-343; Apanteles, Proc. U. S. Nat. Mus. 

 1920, 58 : 483-576; Neoneurinse and Microgasterinae, Proc. U. S. Nat. Mus. 

 1922, 61 : 1-76; Meteorus, Proc. U. S. Nat. Mus. 1923, 63 : 1-44; Microbracon, 

 Proc. U. S. Nat. Mus. 1925, vol. 67, art. 8, 85 pages; Braconinae, Proc. U. S. 

 Nat. Mus. 1927, vol. 69, art. 16, 73 pages; Macrocentrus, Proc. U. S. Nat. Mus. 

 1932, vol. 80, art. 23, 55 pages; and Euphorinae, Misc. Pub. U. S. Dept. Agr. 

 1936, no. 241, 36 pages. 



