Thyreus redactulus? Cockerell

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 : 6-8

Thyreus redactulus? Cockerell figures 4–8

MATERIAL: South India, Coimbatore, 30.iii. 1950, P. S. Nathan. Genitalia dissected and permanently set in slide mount associated with the specimen. Deposited in the Division of Entomology , University of Kansas Natural History Museum. The specimen is almost assuredly an individual of T. redactulus . Nonetheless, I have been slightly hesitant with the identification, as noted by the interogative mark after the epithet, given the distortion of genitalic structures .

COMMENTS: The gynandromorph is on the left side, male; on the right side, female. The left antenna is that of the normal male (i.e., with 13 antennal articles), the right that of the normal female (i.e., with 12 antennal articles). Structural differences between the two sides of the head, mesosoma, and first through fifth metasomal segments are otherwise unremarkable (e.g., figs. 4–6 ). The legs show a mixture of male and female characters, and on the male side the modifications of the metafemora and metatibiae characteristic of species of the takaonis group are not developed. The condition of the apical segments of the metasoma and of the genitalia is more complex.

The metasoma is modified by the apparent loss of the eighth segment on the male side and on the female side by a retrogressive, intersegmental transfer of characters that results in the appearance of a supernumerary exposed segment and in a corresponding decrease in the number of concealed terga, which reduce to one. The principal effect of these modifications is the bringing together in one segment (the seventh) of the male and female halves of the genitalia, the genitalia of the normal male being located between the eighth tergum and the eighth sternum, invaginated within the seventh segment, and those of the female within the sixth segment between the hemitergites of the seventh and eighth segments (which are displaced laterad and modified to form part of the sting mechanism). There are, therefore, seven exposed terga and six exposed sterna.

The sixth segment has the appearance of a normal intermediate metasomal segment. On the right, the special characters of the normal female sixth tergum, in particular the pygidial process, are entirely suppressed.

The tergum of the seventh segment is irregularly developed and, particularly laterally, only weakly sclerotized. The left half tends to the form shown in a normal male, the right half to that shown by the preceding tergum in a normal female, the normal condition, that of a small, wholly invaginated and laterally located hemitergite, being entirely lost. The tergum is fimbriate apically, but a pygidial plate is not developed. The apparent sternum of the same segment is a broad, weakly sclerotized plate, closely adapted on the left to the anteroventral surface of the gonobase and on the right underlying the female genitalia basally. On the female side, neither this sternum (which, with that of the eighth segment, is not present as a separate sclerite in the normal female) nor that of the preceding (sixth) segment shows any tendency toward the highly distinctive form of the sixth sternum in a normal female.

The eighth segment, on the male side, is either entirely lost or, at least, not represented by a separate sclerite; on the female side, the hemitergite approaches the normal form, particularly in the apodeme, but is only weakly sclerotized.

The genitalia ( figs. 7–8 ) are, on the left side, substantially normal male; on the right, abnormal female with male tendencies. The hemitergite of the eighth segment, the second valvifer, the gonoplac, and the rami of the valvulae are relatively little altered and immediately recognizable, the most noticeable modifications lying in the contraction and strengthening of the costal process of the second valvifer and in the expansion of the gonoplac. The second valvula forms an imperfect and twice geniculate stylet ending in a distinct, pointed bulb, which does not, however, represent the bulb of a normal sting but a contraction of the apical part of the stylet. The bulb bears a single, strong seta. The strong, erect, laminar basal process ( fig. 8 ), suggestive of the highly developed sternal apodemes found in Thyreus (cf. fig. 1 ), does apparently represent the right side of the bulb of a normal sting. The equally strongly sclerotized structure ( fig. 8 ), articulated at the base of the sting laterally, is clearly the right half of the furcula. Its presence in addition to the apodeme-like process of the sting, and its free articulation with the base of the bulb, render suspect earlier identifications of the furcula as the ‘‘apodeme of the stylet’’ (and, accordingly, such terminology).

Figures

Figs. 4–6. Thyreus redactulus? Cockerell, gynandromorph. 4. Lateral aspect. 5. Facial aspect. 6. Dorsal aspect.

Fig. 7. Photomicrograph of dissected genitalia of Thyreus redactulus? Cockerell gynandromorph.

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.

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