Xylocopa (Proxylocopa) olivieri Lepeletier

ROZEN, JEROME G. & ÖZBEK, HIKMET, 2003, Oocytes, Eggs, and Ovarioles of Some Long-Tongued Bees (Hymenoptera: Apoidea), American Museum Novitates 3393, pp. 1-36 : 9-10

Xylocopa (Proxylocopa) olivieri Lepeletier

The shape (fig. 8) of the egg of Xylocopa (Proxylocopa) olivieri corresponds closely to published accounts of other members of the genus ( Iwata, 1960, 1964, 1965).

MATURE OOCYTE (figs. 8–11): Length 7.2 mm; maximum diameter 1.7 mm; egg index 1.09 (nearly a giant). Shape elongate, approximately symmetrical around its moderately strongly curved long axis; anterior and posterior ends rounded; maximum diameter about three­quarters length from anterior end, surfaces tapering gradually beyond maximum diameter; micropyle not evident under stereomicroscopic examination but un­ der SEM examination clearly multipored with numerous elongate polygons surrounding it (fig. 10), not unlike the anterior end of the egg of Apis mellifera Linnaeus ( Erickson et al., 1986: 99). Chorion uniformly thin, smooth, transparent, colorless, reflective, lacking sculpturing and other ornamentation under stereoscopic examination; under SEM examination elongate polygonal pattern with raised borders distinct near anterior pole (fig. 10) but only faintly visible elsewhere (fig. 11).

MATERIAL STUDIED: One female, Turkey: Erzurum: 22 km WSW Oltu, VI­25–2001 (H. Özbek) .

REMARKS: The egg size of the subgenus Proxylocopa was of interest because Alvesdos­Santos et al. (2002) hypothesized that gigantism in bee eggs (as defined by Iwata and Sakagami, 1966) may be an adaptation permitting the eggs and early instars to survive in nests in wood. They noted that most wood­nesting xylocopines had giant eggs, as do Hylaeus ( Iwata and Sakagami, 1966) and Tetrapedia . They reasoned that such environments may be subject to loss of humidity and that large egg size might provide more water relative to surface area, thereby safeguarding from desiccation the developing embryo, which becomes a relatively large first instar. Since X. ( Proxylocopa ) is a xylocopine that has reverted to ground nesting, might its egg also have reverted to a smaller size approaching that of solitary, ground­nesting bees?

Although the egg index of this groundnesting xylocopine is 1.09, technically ‘‘large’’, it is so close to the threshold (1.10) of a ‘‘giant’’ that it only questionably supports their hypothesis. Egg indices of other species of Xylocopa provided by Iwata and Sakagami (1966) ranged from 1.38 to 2.00; the range for all Xylocopinae was 1.21–2.00. Alternative explanations, of course, can be cited, namely, gigantism is now built into the genetics of the clade as a sort of evolutionary holdover, or a bank­nesting environment may be subject to unusual drying conditions not normally encountered in horizontal terrain. Other tests of this hypothesis might be the determination of egg indices of such woodnesting taxa as Anthophora (Clisodon) , Centris (Xanthemisia) , and C. ( Heterocentris ) or almost any of the xeromelissines. Michener (1973) recorded the egg sizes of many allopines, but he used a index based on body length; those taxa might be worthy of reexamination

APIDAE : NOMADINAE: AMMOBATOIDINI

Mature oocytes/eggs of this tribe are known from Ammobatoides abdominalis (Eversmann) ( Rozen, 2001) and the two species of Holcopasites described here. They are similar to one another in that they are wide relative to their length, have hook­shaped micropylar processes and a dorsal surface that is somewhat flattened, and exhibit a linear series of pits or fracturelike lines (tentatively called eclosion lines?) arising in front of or just below the micropylar processes and extending partway along the dorsolateral edge of the oocyte on both sides (figs.12, 13). The two species of Holcopasites have rounded front ends as seen in lateral view, with micropylar processes at the most anterior position. In contrast, the anterior end of the mature oocyte/egg of A. abdominalis is drawn out into a curved, sharp point that extends well beyond the micropylar process ( Rozen, 2001: figs. 1, 2, 4, 5). The eclosion lines (?) of H. insoletus (Linsley) seem to be composed of placoid pits that become shallower posteriorly (figs. 12, 14) whereas those of H. tegularis (Hurd and Linsley) appear as fractures that skirt the polygonal edges of the dorsal surface (fig. 13, 15). However, more specimens need to be examined to confirm the consistency of this difference.