Biastes brevicornis (Panzer)

ROZEN, JEROME G. & ÖZBEK, HIKMET, 2003, Oocytes, Eggs, and Ovarioles of Some Long-Tongued Bees (Hymenoptera: Apoidea), American Museum Novitates 3393, pp. 1-36 : 12-13

Biastes brevicornis (Panzer)

The distinctive external shape of the egg of this species is the result of variation in the thickness of the chorion; the shape of the ovum, described below, is unremarkable.

MATURE OOCYTE (figs. 16–20): Length 0.47–0.50 mm; maximum width lateral view 0.19–0.25 mm, maximum width dorsal view 0.19–0.23 mm (see Remarks below); egg index 0.18 (dwarf). The following is based on mature oocytes with the chorion fully deposited, as discussed under Remarks: Shape bilaterally symmetrical; dorsal surface nearly flat to faintly concave behind transverse, thin, lamellate tubercle near anterior end (figs. 16–20); front end slightly swollen because of thick chorion, with micropylar pro­ cess arising anteriorly from swelling; posterior end broadly rounded in lateral view, broader than bulge at anterior end; maximum width as seen from side about midbody, as seen from above closer to front end than midbody; micropylar process elongate, bent dorsally so as to be hook­shaped, with numerous pores (fig. 20). Ovum (fig. 19) somewhat more than twice as long as maximum diameter, approximately symmetrical around its slightly curved long axis with its dorsal surface faintly incurved; maximum diameter near midpoint; ovum tapering anteriorly to rounded front end and posteriorly to more narrowly round rear end. Under stereoscopic examination in ethanol (fig. 16), chorion highly reflective, smooth (except for dorsal tubercle and micropylar process), colorless, and clear; that of dorsal surface glassy, very thick toward rear, becoming somewhat thinner anteriorly; after critical­point drying, chorion on dorsal surface appearing slightly yellowish, indistinctly pebbled on surface, sides and ventral surfaces smooth, highly reflective; under SEM examination (fig. 19), chorion dorsal surface with faint polygonal pattern over most of area; side and ventral surfaces with faint polygonal pattern (fig. 18).

MATERIAL STUDIED: One female, Turkey: Erzurum, Atatürk University Campus , VI­ 29–2001 (J.G. Rozen) .

REMARKS: In recent papers the term ‘‘mature oocyte’’ has referred to Iwata’s (1955) category A and B oocytes ( Alexander and Rozen, 1987) or to oocytes that have wellformed, thick chorions (e.g., Rozen, 2001). Most cleptoparasitic bees seem to have an unusually thick chorion, and this is especially true of the eggs of Biastes brevicornis (although it may generally be true for Nomadinae, as it is for Dioxys cincta , above). The mature oocytes recorded for this species are those with a detectable chorion and an evident micropylar process. However, we note a gradation in the development of the dorsal tubercle, the thickness of the dorsal chorionic surface, and the anterior chorionic bulge, with the later mature (lower in the ovarioles) oocytes having the chorion thicker in these areas, accounting for the variation in the dimensions. Earlier mature oocytes have small­ er tubercles, even though the chorion else­ where is evident and the ovum has reached its full size. Thus, there are degrees of maturity among those oocytes classified as mature oocytes. It follows that the amount of time required to deposit a thick chorion may be far greater than that for a thin­walled, nonparasitic bee egg. Of the 32 mature oocytes (table 1), that is, those with an evident chorion, 13 had a fully or nearly fully developed dorsal tubercle.

Egg placement of Biastes brevicornis in the host nest has not been observed. However, from the shape of the mature oocyte, it seems likely to be similar to egg placements of tribal relatives Neopasites cressoni (Torchio et al., 1967) and Rhopalolemma rotundiceps ( Rozen et al., 1997) ; that is, the long axis of the egg parallel to the brood cell wall, the dorsal surface of the egg exposed to the cell lumen, and the remainder of the egg hidden in a groove in the cell wall.

APIDAE : NOMADINAE: AMMOBATINI

The mature oocytes of the Ammobatini show considerable morphological variation. All possess a more or less well­defined opercular area at the anterior end. This area may be flat, curved, or even slightly concave, and it may be variously ornamented with tubercles and patterns. depending on the taxon. The operculum may be surrounded by a flange (figs. 26, 41), which in most taxa is a single extended sheet of the chorion that, in a deposited egg, overrides the cell wall where the egg is inserted ( Rozen, 1986b: fig. 6). In the mature oocyte, however, the flange hangs close to the body of the oocyte. The flange is broad in the case of Sphecodopsis (Pseudodichroa) or more limited as in the case of Pasites maculatus Jurine (fig. 44), Parammobatodes rozeni Schwarz (fig. 37), and ‘‘ Parammobatodes ’’ orientana (Warnke) (fig. 41). In Oreopasites favreauae Rozen (fig. 25), O. barbarae Rozen (fig. 32), and O. linsleyi Rozen (fig. 35), the flange is incomplete, represented only along the anterior edge and sides of the operculum but not in the rear. The flange is totally missing in O. vanduzeei Cockerell (fig. 30) (as it may be in Ammobates carinatus Morawitz ), but is replaced with a thick opercular rim. All taxa examined except for the two species of Sphe­ codopsis (Pseudodichroa) exhibit dorsal transverse folds of the chorion toward the posterior end, a feature apparently unique to this group of cleptoparasitic bees. These folds allow the egg to be bent back on itself at the time of deposition. Oocytes of Pas. maculatus (fig. 47), Par. rozeni (fig. 38), and ‘‘ Par.’’ orientana (fig. 43) possess micropyles consisting of a single pore; micropyles of other tribal members are multipored. The mature oocytes of Pas. maculatus and the ‘‘ Par.’’ orientana can obviously be distinguished on the basis of their different sizes, but they are quite similar in shape and structure. Opercular tubercles of Pas. maculatus (fig. 45) are larger than those of ‘‘ Par.’’ orientana (which in fig. 42 are scarcely discernible), although the extent of expression of these tubercles appears to be subject to variation in size from one oocyte to the next in some taxa. The polygonal opercular pattern of the latter (fig. 42) seems to contrast with the unpatterned opercular surface of Pas. maculatus (fig. 45) under SEM examination. The huge, strongly tuberculate, amber operculum of A. carinatus (fig. 21) distinguishes this species from all others treated here, as does the flat ebony­colored operculum of Par. rozeni (figs. 36, 37).