Author: SMITH EDWARD LAIDLAW
Publisher: Entomological Society of America
ISSN: 1938-2901
Source: Annals of the Entomological Society of America, Vol.63, Iss.1, 1969-01, pp. : 1-27
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Abstract
The Hymenoptera have the least sexually dimorphic combined with the least specialized genitalia among the Pterygota. The only major female modifications are: (1) a shift in the articulation of gonocoxite IX to gonocoxite VIII; and (2) reduction ( and elimination in Apocrita) of (coxo) sternites V11I and IX. Subsequent changes have tended toward: (1) secondary flexion between abdominal segments I and II of Apocrita to facilitate use of long gonapophyses (ovipositor), and (secondarily) to sting; (2) withdrawal of the gonapophyses beneath the abdomen into a fold resulting from the desclerotization of the genital coxostcrnites (Symphyta), and ultimately, invagination with the terminal abdominal somites together with a mesal division of their tergites (Apocrita) ; (3) shortening and reduction of the gonostyli to (usually) 1 segment; (4) dimorphism in the 2 pairs of gonapophyses and modification of simple segmented tubes to laterally compressed, toothed blades; (5) enlargement and subdivision of the teeth on the gonapophyses in Symphyta, and development of patterns in proprioceptive sensilla on them, reflecting that; (6) penetration of the substrate by the gonapophyses (of many sawflies, at least) is through their spring-loaded rami, teeth and annuli acting as a vibratory wedge; and (7) modification of the colleterial glands into producers of gall-inciting substances (some Symphyta—Tenthredinidae), or toxic materials (Aculeata) ; the ovipositor has lost its egg-laying function in the latter and becomes the sting. Major modifications in the male have been: (1) disarticulation of gonocoxite IX from tergite IX and reattachment to sternite IX; (2) mesal fusion of parts of the 2 gonocoxites, and transverse separation of some of the compound sections; (3) mesal fusion of the olistheter components of gonapophyses IX (rhachies) ventrally to form a tube out of the appendages; and (4) development of pincers on the distal portions of Section 3 of the gonocoxites. Subsequent evolution in the male has included: (1) redivision of gonapophyses IX ventrally, restoring the separate identities of the appendages from the derived tubular structure; splitting was by a separation between the ventral rami laterally and the mesal fused rhachies rather than through redivision of the rhachies; the resultant detached, united rhachies appear as a separate sclerite in primitive Symphyta, lower Apocrita, and males of some other Holometabola; (2) the fused dorsal rami (notum) of gonapophyses IX of Tenthredinoidea have become desclerotized, allowing independent motion of the appendages; (3) the projections on Section 3 of either gonocoxite have become opposable pincers (volsellae), but degenerated or became otherwise modified in many higher Aculeata; and (4) the gonostyli of Aculeata have tended to lose their musculature, and have become closely attached to the gonocoxites.
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