Paracolletes crassipes SMITH

Rozen, Jerome G. & Houston, Terry F., 2022, Descriptions of the Mature Larvae of Three Australian Ground-Nesting Bees (Hymenoptera: Colletidae: Diphaglossinae and Neopasiphaeinae), American Museum Novitates 2022 (3989), pp. 1-16 : 8-13

Paracolletes crassipes SMITH

Figures 14–22

DIAGNOSIS: Like most Diphaglossinae (and unlike all Neopasiphaeinae ) in having labium extending forward to front of head and bearing a projecting salivary spout with circular, apical opening (figs 15–19); epistomal ridge (figs. 15, 16) strongly expressed.

HEAD: Small compared with body (figs. 14, 21). Posterior margin of head capsule distinct on cleared and stained specimen; external impression of epistomal ridge not strong but inter- nally ridge extremely well developed as seen on cleared head capsule (figs. 15, 16); this ridge thick, long, curving slightly upward between widely separated anterior tentorial pits but remaining somewhat below level of antennae (fig. 15); median coronal ridge absent; parietal bands only moderately impressed (figs. 15); integument mesad of each band not produced as mound; antennal mounds weakly expressed (fig. 16); anterior surface of clypeus in lateral view (fig. 16) continuing slope of frons. Labrum moderate in size, bearing pair of moderately sized, widely separated, apical tubercles (fig. 15). Mandibular apex elongate, darkly pigmented, gradually tapering to narrowly rounded apex; apical dorsal edge with numerous sharp teeth; ventral apical edge smooth, without teeth. Maxillae (fig. 18) moderately large, each with tapering elongate pigmented palpus. Labium large, projecting (figs. 16, 22) with paired, pigmented palpi that are almost as large as maxillary palpi. Circular salivary opening apically positioned on large, conspicuous, projecting spout (figs. 16–19); outer surface of spout translucent, seemingly pigmented because of internal, darkly infuscate salivary duct. Labial apex and salivary opening forming complicated structure described in further detail in Discussion section, below.

BODY: As explained below, general body form of postdefecating larva impossible to generalize because of various deformities presumably imposed by cocoon constraints. In lateral view (fig.

14) body segmentation accentuated but intraseg-

mental subdivisions much reduced with posterior annulets projecting farthest and each bearing slightly elevated modified integument forming transverse band on each side of segments. When stained with ethanol solution of Chlorazol Black

E, these transverse bands on each side of body becoming much more distinctive.

MATERIAL EXAMINED: Four postdefecating larvae: ex cocoon January 2021, excavated Dec.

29–32/i/20- 20, 10 km ENE of Waroona, W.A.

32.9705° S, 116.0099° E, T. F. Houston 1578-7 .

DISCUSSION: The inclusion of this species in the Diphaglossinae is supported by the fact that its mature larva spins a cocoon ( Houston

2020c) while larvae of other colletid subfamilies

(with one exception) are not known to do so.

Moreover, the anatomical features associated with cocoon-spinning in this species are characteristic of the subfamily: namely the projecting labium with its salivary spout and circular,

ringed, apical opening (figs 16–20).

With most other cocoon-spinning bees the larval salivary opening is a transverse slit formed by projecting transverse lips (as found on divergently related bee larvae (e.g., Melitta

( Rozen and McGinley, 1974, figs. 20, 21); Dioxys

( Rozen, 1967. figs. 6–8); and Xenoglossa and

FIGURES 17–19. SEM micrograph of mouthparts of Centris ( Rozen, 1965, figs. 11, 12, 55, 56).

postdefecating larva of Paracolletes crassipes . 17.

Oral view. 18. Close-up of labium and surrounding Early on, Michener (1953) pointed out structures. 19. Ventral view. and illustrated spoutlike salivary openings on mature larvae both of Policana herbsti Friese

(now Cadeguala albopilosa (Spinola))

( Michener, 1953: figs. 37, 38) and Caupolicana gayi (Spinola) ( Michener, 1953: figs. 40, 41).

More than a quarter century later McGinley (1981) expanded the listing with Ptiloglossa fulvopilosa Cameron , P. guinnae Roberts , and P. jonesi Timberlake. He allowed that Policana herbsti belonged to this group in spite of the fact that its salivary opening was “flattened and transverse.” However, as clearly shown by illustrations of the larva of this species ( Michener,

1953: figs. 37, 38), the labium strongly projects and the salivary opening is a spout.

In cocoon spinning P. crassipes , the spout projects, but in others that are nonspinners, like Trichocolletes orientalis (figs. 12, 13) above, the external salivary opening is thought to be a simple circular hole on the labial apex that closes when its upper edge bends down reducing the aperture to a small, curved slit.

Each of the four preserved specimens of P. crassipes (fig. 20) was anatomically strongly curved, contrasting with the uniformly elongate linear posture of preserved postdefecating larvae of the other subfamilies (e.g., figs. 1, 9). The variously bent, physogastric shapes of larval P. crassipes (figs. 20, 21) presumably FIGURE 20. Microphotograph of the four preserved postdefecating larvae of Paracolletes crassipes showresulted from their being physically con- ing body distortion attributed to being confined by fined by their cocoons. On cleared, stained their cocoons when first preserved, contrasting with specimens, the strongly expressed internal shape of postdefecating larvae of Leioproctus wanni epistomal ridge (figs. 15, 16) immediately (fig. 1) and of predefecating larva of Trichocolletes orientalis (fig. 9). separates this species from those of known Neopasiphaeinae . The labial apex of larval P. crassipes consists of a number of elements that require description because they differ from those of noncocoon spinners of other colletid subfamilies. In P. crassipes (figs. 17, 19) the paired labial palpi are tapering and elongate, nearly as long as the maxillary palpi. Centered between them is the protruding, slender, tapering, unpigmented, and therefore nearly transparent salivary tubercle housing a long inner, parallel-sided, more or less darkly infuscate duct of the salivary gland, features not revealed in figures 17–19 because they are opaque SEM micrographs. The nearly transparent salivary outer tubercle and inner duct of the salivary gland join apically forming a conspicuous circular hole, i.e., the opening of the salivary spout (fig. 19) where they provide a ringed circular apex. Although the SEM micrograph (figs. 17–19) gives the impression of two openings, one above the other, a careful reexamination of the apex on an untreated specimen clearly reveals only a single aperture, thus indicating that the lower, apparent opening on the micrographs is an accidental artifact. This same round, ringed opening to the salivary gland was observed in the case of Trichocolletes orientalis and perhaps Leioproctus wanni suggesting a similar internal structuring but without the projecting shape. In addition to the pronounced labial tubercles and protruding salivary opening of P. crassipes , a highly magnified view of the apex of the labium (figs. 18, 19) also reveals more, though smaller projections. These are seemingly tipped with sensilla, perhaps raising interesting but unanswered questions about their function and/or consistency of the food material.

PRESUMED FUNCTION Of NEST ARCHITECTURE Of Paracolletes crassipes SMITH

One of us ( Houston, 2020c) provided significant detailed information on the in-ground nest structure of P. crassipes that explains not only how the particular architecture functions for this species, but also how it serves other taxa as well. As he pointed out, the descending main burrow of the nest is not lined with a coating that provides a water repellent surface, nor do the laterals leading to cells have such a complete lining. However, with certain taxa, before each lateral reaches a cell, it curves upward and then bends downward to connect to the cell. Significantly, the surface of the bending lateral is lined and airtight as is the lining of the cell wall to which it connects. If heavy rains occur during the active nesting period, water flowing along the ground surface that reaches a nest entrance will flow into the main descending nest burrow and possibly into laterals leading to cells. However, when reaching the lined upward bend at the far end of a lateral, flowing rainwater will be blocked from entering the cell by the trapped chambered air in the upward bend and connecting cell. The amount of air thus trapped in a cell during a rain is likely sufficient to sustain the preemerged bee until the passageway to the cells is no longer flooded.

It is here proposed that air trapped in the upswing of a lined lateral where it connects to a cell may be a mechanism that allows the inhabitant of the cell to survive during periods of severe precipitation during the nesting season. Although Roberts (1971: fig. 3) correctly and fully diagramed the cell and its coated inverted U-shaped connection to the lateral tunnel in the nest of Ptiloglossa guinnae Roberts , neither he nor anybody else has explained the mode of action of the system, namely, the air enclosed in the cell and its airtight, lined, inverted U-shaped connection to the lateral is blocked from escaping, barred by the water- and airtight lining of the cell and its connecting upward loop to the lateral. Examples of the possible use of this mechanism revealed from J.G.R.’s research are listed in table 2. Based on research by Sarzetti et al. (2013, 2014) it is likely that this mechanism has been extensively employed by the Diphaglossinae .

Although the listings in table 2 contain only a few examples, the examples seem to include mostly large-bodied taxa with large burrow diameters. This may suggest that small-bodied taxa using small burrow diameters may be at less risk, perhaps because burrow entrances smaller in diameter do not accommodate as much runoff water compared with the length of tunnel surface available to absorb the runoff before it reaches the cell entrance. Furthermore, with bees nesting in unconsolidated porous ground, falling water will tend to be absorbed by the soft earth rather than forced to channel over the surface and thereby pour into encountered nest entrances. In addition, nest entrances on vertical surfaces are shielded from surface water runoff and even entrances on sloping surfaces are somewhat protected, especially if the entrance burrow is horizontal as it extends into the ground.

Table 2 lists published descriptions of bee nests that display tunnels leading to cell entrances that routinely rise and then turn downward before connecting to cell entrances. They therefore possibly protect the cell from flooding, a prediction that can be confirmed if the bend in the tunnel proves to be airtight.

Figures

FIGURES 14–16. Diagrams of postdefecating larva of Paracolletes crassipes Smith. 14. Full body, lateral view. 15, 16. Head, frontal and approximate lateral views.

FIGURES 21, 22. Microphotograph of head and body, lateral views, of a live postdefecating larva of Paracolletes crassipes, revealing texture and color as well as shape of integument.