Braconids And Ichneumons

Present data on numbers of species ranks the Ichneumonoidea as the largest superfamily of Hymenoptera. It includes the bulk of the larger Parasitica, most ichneumonoids being over 5 mm in length and a few being longer than 50 mm. A greater percentage of Ichneumonoidea than other Parasitica have the ovipositor conspicuously exposed, but, on the other hand, a very significant portion of Ichneumonoidea have ovipositors that protrude scarcely or not at all beyond the median dorsal extremeties of the apical tergites. Townes (1975) discussed the Hymenoptera (mostly Ichneumonoidea) with the longest ovipositors; he cited a species of "Iphiaulax?" (Braconidae) with an ovipositor 14 times the length of the body. ~The distinguishing characters of Ichneumonoidea are: the usual fusion of the costal and subcostal veins of the fore wing; the long antennae, which are usually more than 14-segmented; and the 2-segmented hind trochanters (the other trochanters usually also being 2-segmented). The characters are for the most part shared by the Braconidae, Aphidiidae, Hybrizontidae, Ichneumonidae, and Stephanidae, the five families here considered to comprise the Ichneumonoidea. In the case of the Stephanidae, however, there is some question about the correctness of placement in the Ichneumonoidea (see Townes, 1969, p. 3). The larval head capsule of stephanids is considerably different from those of other ichneumonoid families (personal commun., J. R. T. Short, 1976), and in stephanids the costa and subcosta are more distinctly separated than in other ichneumonoid families. Nevertheless, we believe it best to leave the Stephanidae in the Ichneumonoidea until further studies are made. ~The Aphidiidae and Hybrizontidae are sometimes treated as subfamilies of Braconidae (see van Achterberg, 1976). Some early 19th Century authors referred to the combination of the latter three groups as the "Ichneumonidum adscitorum" (?unauthentic Ichneumonidae) which they distinguished from the "Ichneumonidum genuinorum" (genuine Ichneumonidae). The distinction largely resulted from Jurine's (1807) classification of the veins and cells of hymenopterous fore wings and his provision of terms for some of the veins and cells (e.g. "nervi recurrentes"). Eady (1974) provided an excellent discussion of the way in which the Jurinean system of wing vein and cell nomenclature was modified and expanded by those who adopted Jurine's ideas. He reviewed the systems of wing vein nomenclature which are currently used for Braconidae and compared them with usages for Aphidiidae, Ichneumonidae, and other Hymenoptera. He proposed an "interim method [in order] to overcome the more frequently voiced objections to ... [the Comstock-Needham] system without adding to the confusion or obstructing progress toward uniformity." ~It was apparently by mutual agreement that Gravenhorst (1819) and Nees ab Esenbeck (1819) decided to specialize on the Ichneumonidorum genuinorum and Ichneumonidorum adscitorum, respectively. In the papers referred to, they simultaneously outlined their plans for the monographs which are here cited in the sections to which they pertain. Thunberg (1822, 1824) chose to ignore the revolutionary advances in classification made possible by the work of Jurine and reverted to lumping all of the Ichneumonoidea under the generic name Ichneumon (see introduction to Ichneumonidae). Consequently, Thunberg's work was largely ignored prior to Roman's (1912) study of his type specimens. ~The actual number of species in the Ichneumonoidea can only be estimated. The Braconidae contains about 2,000 described species in North America and about 10,000 worldwide; the Ichneumonidae about 3,000 in North America and about 15,000 worldwide. However, the total number of species is estimated to be 60,000 worldwide in the Ichnuemonidae (Townes, 1969, p. 7) and 40,000 in the Braconidae. ~Except for Hybrizontidae and Stephanidae, the families of Ichneumonoidea occur in all zoographical regions and in all terrestrial habitats. In the Ichnuemonidae the Western Palearctic fauna is best known followed by the Nearctic, whereas the reverse seems to be true for the Braconidae. As in the case of Chalcidoidea, most of our knowledge of the Ichneumonoidea has been derived from species of economic importance to agriculture. For the vast majority of species, there is little or no knowledge of biology. ~The ichneumonoids are parasitic on nearly all groups of insects as well as on spiders, and all stages of these hosts are attacked. Aphidiidae, many Braconidae, and possibly Hybrizontidae (hosts of latter unknown) attack paurometabolous insects, while no paurometabolous hosts are known for Ichneumonidae or Stephanidae. The only ichneumonoids which attack adults of holometabolous insects are certain euphorine and blacine Braconidae. Aside from the limitations which have been mentioned, large numbers of Ichneumonoidea are polyphagous and the limits of the host range seem to be related more to the host habitat than to the taxonomy of the host. ~The only families of Ichneumonoidea which are known to include hyperparasitic species are Ichneumonidae and Braconidae, but only a very few Braconidae could be regarded as hyperparasitic (i.e. a few Euphorinae which attack adult Ichneumonidae). The fact that hyperparasitism is much more prevalent in the Ichneumonidae than in the Braconidae is explained largely (but not in the case of mesochorine and eucerotine Ichneumonidae) by the fact that certain Ichneumonidae have the habit of attacking hosts which are confined within silken cocoons (e.g. sawfly prepupae, ichneumonoid prepupae, spider eggs, chrysopid eggs, etc.), while this habit has not developed among Braconidae. Further discussion of host relations is deferred to the introductions to the various taxa.