Thyreus, STING

ENGEL, MICHAEL S., 2007, A Lateral Gynandromorph in the Bee Genus Thyreus and the Sting Mechanism in the Melectini (Hymenoptera: Apidae), American Museum Novitates 3553 (1), pp. 1-12 : 3

THYREUS STING MORPHOLOGY

Thyreus ramosus (Lepeletier de Saint Fargeau) figures 1–3 , 9

COMMENTS: Tergites VII and VIII are dissociated into lateral, sclerotized hemitergites, their medial, dorsal areas becoming membranous and elastic to accommodate the movements of the sting and associated structures during exsertion. Although completely invaginated within the genito-anal atrium, the seventh hemitergite retains its spiracular openings; in the eighth hemitergites, they are lost. The hemiterigites of the seventh metasomal (last spiracular) segment are small and weakly sclerotic. They occupy a lateral position between the lateral processes of the sixth sternum (with which they are loosely articulated, this articulation forming the pivot on which the sting mechanism rotates when the sting is exserted) and the basal extremities of the apodemes of the hemitergites of the eighth segment, with both of which they are loosely connected (cf. figs. 1 , 2 ). The hemitergites of the eighth segment are relatively large, weakly sclerotic, and broadly united with their equally large, scaphoid apodemes. Dorsally, each hemitergite becomes membranous and is applied to the outer surface of the apical half of the second valvifer; postero-ventrally, it articulates with the small, strongly sclerotic gonangulum. The second valvifer consists of a rigid, well sclerotized anterior costa, which articulates laterally with an angular projection of the gonangulum and is prolonged dorsoapically in the distinct, terminally hamate costal process (where the proctiger connects) and a broad, membranous limb from which arises, dorso-apically, adjacent to the costal process, the gonoplac. The gonoplac consists of a simple basal article (or stylifer) and a distinct, more strongly sclerotized, setigerous apical article (or orthostylus). The gonangulum and second valvifers give rise ventrally to the first and second valvulae. The rami of the valvulae are slender, elongate, and in contact throughout their length—that of the second valvula supports the ventral margin of the limb of the second valvifer. The sting (comprising the lancets of the first valvulae and the stylet of the dorsally fused second valvulae) is long and heavy and occupies the whole length of the sixth sternum. The furcula is broad, subcordate, and apically appendiculate, and its two arms are closely but freely articulated at the sides of the bulb of the stylet basally (cf. fig. 9 ).

Figures

Fig. 1. Thyreus ramosus (Lepeletier de Saint Fargeau), dorsal view of female metasoma depicting genitalia in situ. Scale bar 5 1 mm.

Figs. 2, 3. Thyreus ramosus (Lepeletier de Saint Fargeau), female, lateral view of genitalia, setae omitted; seventh hemitergite not shaded or stippled; eighth hemitergite densely shaded; gonangulum solid black; second valvifer stippled; furcula, sting, and sixth sternum (except anterior weakly sclerotized area) densely stippled. 2. Position of sclerites with sting retracted. 3. Position of sclerites with sting exserted (the sting is shown drawn away from the sting guide to make the relative positions of the furcula and the rami of the valvulae clearer). Scale bars 5 1 mm.

Figs. 8, 9. Genitalia of Thyreus species. 8. Thyreus redactulus? Cockerell, gynandromorph, dorsal view. 9. Thyreus ramosus (Lepeletier de Saint Fargeau), female, genitalia and right seventh hemitergite, oblique dorsal view (lateral halves of genitalia slightly separated). Scale bars 5 1 mm.