Stelis ater (Hall and Ascher, 2010)

Rozen, Jerome G. & Hall, H. Glenn, 2011, Nesting and Developmental Biology of the Cleptoparasitic Bee Stelis ater (Anthidiini) and Its Host, Osmia chalybea (Osmiini) (Hymenoptera: Megachilidae), American Museum Novitates 2011 (3707), pp. 1-40 : 30

STELIS ATER

EGG/MATURE OOCYTE

Figures 35 , 73, 76, 77

DIAGNOSIS: Eggs/mature oocytes have been described for Stelis elongativentris ( Rozen, 1987) and S. (Stelis) murina Pérez ( Rozen and Kamel, 2009) . Those of S. ater are remarkably similar in color and shape, all characterized by their shortness relative to maximum diameters, rounded front ends, and slightly more narrowly rounded posterior ends. Of the three species, those of S. ater are the longest.

Eggs of Stelis ater can be immediately distinguished from those of the host by shape and size. Those of Osmia chalybea are substantially longer, and their maximum diameter is posterior to midbody as seen in lateral view (figs. 70, 71) rather than at the midbody as in S. ater (fig. 72).

DESCRIPTION: Length 2.2–2.4 mm; maximum width 0.88–0.98 mm (N = 5) at approximate midbody. Shape slightly curved with ventral surface flat to slightly concave in lateral view; anterior end broadly rounded in lateral view; maximum breadth at midbody with posterior half tapering to slightly more narrowly round posterior end in lateral view (fig. 72); micropyle a disc (fig. 77) surrounded by converging ridges on normally curved surface of front of egg at anterior pole (fig. 76) not visible under stereomicroscope; apparent absence of pores not understood. Egg color translucent whitish; chorion under stereoscope clear, shiny, glassy. Under SEM examination chorion featureless except for micropylar area.

Figures

FIGURES 35–40. Immatures of Stelis ater. 35. Egg deep in provisions; eggs were encountered both in the provisions and on the front surface of the provisions, as discussed in text. 36. Early instar (arrow) deep in the provisions and feeding larva of Osmia chalybea (right) on front surface of provisions. 37. Egg of Stelis ater (arrow) and probable first instar of Osmia chalybea (left) on front surface of provisions with trachea now visible. 38. Same cell some time later with Stelis ater (arrow) now early feeding instar having not yet encountered Osmia chalybea, which has become an intermediate instar. 39. Early instar of Osmia chalybea being attacked simultaneously by two early instars of Stelis ater; one of which (arrow) is barely visible to the left of the others. Presumably one S. ater larva would later kill the other, since we never found more than one cocoon in a cell. 40. Two feeding early instars of Stelis ater (arrows) from eggs deposited deep in provisions.

FIGURES 73–77. SEM micrograph of anterior ends of eggs of Osmia chalybea and Stelis ater. 73. Anterior pole of egg of O. chalybea. 74. Micropylar area of same identified by rectangle in figure 73. 75. Close-up of micropylar disc of same. 76. Anterior pole of Stelis ater. 77. Micropylar area of same identified by rectangle in figure 76.