Conanthalictus bakeri, Crawford

Rozen, Jerome G. & ÖZbek, Hikme T., 2008, Immatures of Rophitine Bees, with Notes on their Nesting Biology (Hymenoptera: Apoidea: Halictidae), American Museum Novitates 3609 (1), pp. 1-36 : 24-27

bakeri Crawford

Figures 64–69

DIAGNOSIS: The rounded body tubercles of this species easily separate it from the more pointed tubercles of Conanthalictus conanthi .

The larval mandibles of the two species of Conanthalictus treated here differ from those of all other rophitines in that the mandibles are interpreted as having a conspicuous subapical tooth in addition to smaller teeth extending along the apical dorsal edge both proximal and distal to the subapical tooth. We have re-examined specimens of both and think that this interpretation is still appropriate since the subapical tooth is substantially larger than all other teeth along the dorsal edge in the two species. Interestingly, when the mandible of the predefecating larva of C. bakeri was re-examined with a compound microscope, it, like that of C. conanthi , appeared to have no teeth along the ventral apical edge. Yet, the SEM micrograph (fig. 68) of the predefecating larva clearly has two teeth along this edge.

In the following, comparisons with Conanthalictus conanthi refer to the description presented by Rozen (1993).

HEAD (figs. 66, 67): Integument of head capsule with scattered small sensilla that are not obviously setiform. Integument unpigmented except for mandibular apices.

Head size (figs. 64, 65) moderately small compared with body size; head capsule much wider than length measured from top of vertex to lower clypeal margin in frontal view. Unlike that described for Conanthalictus conanthi , tentorium complete, including dorsal arms. As in C. conanthi , anterior tentorial pit close to anterior mandibular articulation; posterior tentorial pits in normal position; postoccipital ridge weak, evident only near posterior tentorial pit, vanishing dorsally (perhaps more quickly in postdefecating larva than in predefecating larva); median longitudinal thickening of head capsule absent; hypostomal ridge moderately developed; pleurostomal ridge well developed; epistomal ridge laterad of anterior tentorial pit extremely short because of closeness of pit to anterior mandibular articulation; ridge between pits either absent (postdefecating larva) or present but fading well before median line (predefecating larva). Parietal bands evident both as integumental scars and as subcutaneous white imaginal discs on uncleared specimens, unlike those of C. conanthi . As in C. conanthi , antennal prominence large, globose, occupy- ing much of anterolateral area of parietal, though not strongly projecting; antennal disc and papilla moderately large; papilla projecting slightly, bearing 3–4 sensilla. Vertex evenly rounded as seen from side, without projections. Labrum not projecting as far as clypeus in lateral view (fig. 67), very short in frontal view (figs. 66, 68); labrum and epipharynx apparently without spicules.

Mandible similar to that of Conanthalictus conanthi ( Rozen, 1993: figs. 38, 39) with conspicuous, sharply pointed subapical tooth and with series of sharp teeth along dorsal apical edge (see ‘‘Remarks’’ for further explanation of mandibular apex); ventral apical edge with one or two minute teeth; cusp not developed; apical concavity scarcely developed, a flattened area near mandibular apex; outer mandibular surface with one or two, small, inconspicuous tubercles, each bearing single short sensillum. Labiomaxillary region greatly recessed, as in C. conanthi . Maxilla with dorsal surface spiculate; cardo, stipes, and articulating arm of stipital sclerite not evident; maxillary palpus recognizable only by several sensilla at maxillary apex. Labium (unlike that described for C. conanthi 7) weakly divided into prementum and postmentum,

7 Examination of the postdefecating larva of Conanthalictus bakeri raises the possibility that the prementum/ postmentum boundary of C. conanthi was confused with the posterior boundary of the postmentum ( Rozen, 1993: fig. 35). Reexamination of the head of C. conanthi in the collection of the AMNH confirms that there is a ventral line approximately in line with an imaginary line drawn from the vertex through the posterior tentorial pit, as illustrated (loc. cit.). However, in C. bakeri , the posterior margin of the postmentum is clearly behind this imaginary line; another transverse ventral line anterior to it is considered to demark the prementum/postmentum boundary. In other rophitines, the posterior margin of the postmentum falls behind this imaginary line. At the same time, if the labial length depicted in (loc. cit.) is actually only the length of the prementum, then it is disproportionately long compared with that shown in fig. 67 for C. bakeri .

moderately long; labial palpus not evident except for several sensilla. Salivary lips absent; opening of salivary duct a transverse slit, narrow on postdefecating specimen but wide on predefecating specimen. Hypopharynx nonspiculate, not longitudinally grooved; hypopharyngeal groove absent (alternatively the wide salivary opening may possibly be the median remnant of the hypopharyngeal groove, with the salivary duct opening into it).

BODY: Integument with fine scattered nonsetiform sensilla; many areas with fine, widely and evenly spaced spicules; dorsal body tubercles faintly wrinkled apically. Body form (figs. 64, 65) moderately robust; intersegmental lines moderately weakly incised on predefecating form; on postdefecating form ventral intersegmental lines modified as explained under ‘‘Remarks’’, below; as in Conanthalictus conanthi , paired prothoracic dorsal tubercles absent; mesothorax, metathorax, abdominal segments 1–8 with paired dorsal tubercles (figs. 64, 65), which are conical rather than transverse; venter of abdominal segment 9 scarcely produced ventrally; abdominal segment 10 oriented apically on 9, with dorsal surface shorter than ventral surface, so that anus directed somewhat dorsally; venter of 10 of postdefecating larva with faint transverse line. Spiracles very small, without sclerites, not on tubercles; peritreme present, narrow; atrium projecting slightly beyond wall, with rim, globose; atrial wall smooth; primary tracheal opening with collar; subatrium normal in length, consisting of about 10 chambers. Male with distinct median, transverse, integumental scar ventrally near posterior margin of segment 9; female sexual characters unknown.

MATERIAL STUDIED: 1 postdefecating larva, USA: Arizona: Pima Co.: Organ Pipe Cactus National Monument, August 15, 1995 (J.G. Rozen and S. Budick); 1 probably early last larval instar, same, except April 1, 1995 (J.G. and B.L. Rozen) .

REMARKS: JGR discovered a nest of Conanthalictus bakeri (adult collected and identified) on March 25, 1995, at Organ Pipe Cactus National Monument, Pima County, Arizona, and excavated it the next day. Two immature larvae from it were reared for several days after excavation but were preserved on April 1, 1995, because they were not faring well. At least one of these appeared to be an early-stage last larval instar; it is described here, its identity certain. Later the same year, JGR again visited the National Monument and retrieved a single mature Conanthalictus larva from a nest marked in the spring. No adult voucher specimen was associated with the nest. Although the larva appears to be that of C. bakeri , adults of C. deserticola Timberlake were also common in the spring. Thus, the postdefecating larva described here is possibly C. deserticola . The differences between these two larvae are discussed under ‘‘Remarks’’, below.

Michener’s statement (2000) that Conanthalictus has a fused prementum and postmentum was based on only C. conanthi as reported by Rozen (1993). The prementum is weakly separated from the postmentum in C. bakeri .

Although the postdefecating and predefecating larvae described here are nearly identical, they do differ beyond what one usually sees between these two life phases. The peculiar, accordion-like ridges nearly paralleling the ventral intersegmental lines on many of the abdominal segments of the postdefecating form (fig. 64) are without precedent among bee larvae and probably resulted from a postmortem change, the specimen having expanded in the preservative. Presumably the intersegmental lines would be concealed in life, a coarctation that perhaps serves as a defense mechanism to protect a diapausing individual from attack or dehydration. It seems unlikely that an active, functioning bee larva would have such ridges, and they certainly are not present on the predefecating larva (fig. 65). The ridges are integumental in nature since they persisted even after the specimen was cleared in an aqueous solution of sodium hydroxide.

The apices of the 10th abdominal segments of the postdefecating (fig. 64) and predefecating (fig. 65) larvae appear dissimilar. However, while clearing the predefecating larva in an aqueous solution of sodium hydroxide, we discovered that the anus is very large, and the soft, perhaps rectal integument surround the anus appears capable of everting during defecation. The roughened area surrounding the wide, slitlike anus on the postdefecating larva is thus interpreted to be the shriveled soft rectal integument.

The labiomaxillary regions of the two larvae also appear different, but this may be due to postmortem modifications of the more pliable integument of the feeding larva.

Two differences appear to be unrelated to larval stage. The predefecating larva has three sensilla on each antenna, and the postdefecating larva has four sensilla on each. The predefecating larva shows the internal epistomal ridge advancing part way mesad of the anterior tentorial pit, while the median section of the internal epistomal ridge is completely absent in the postdefecating larva (fig. 66), as in Conanthalictus conanthi ( Rozen, 1993: fig. 36). More larval specimens of C. bakeri and C. deserticola are needed to determine whether these differences are intraspecific or interspecific.

Figures

Fig. 64. Postdefecating larva of Conanthalictus bakeri? (specimen not certainly identified to species; see text). Fig. 65. Predefecating larva of C. bakeri (specimen certainly identified to species). Figs. 66, 67. Head of postdefecating larva of C. bakeri?, frontal and lateral views, respectively. Scale refers to figs. 64, 65.

Figs. 68, 69. SEM micrographs of predefecating larva of Conanthalictus bakeri? 68. Labrum, right side, and right mandible, frontal view, showing tubercle on outer surface and bifid apex of mandible. 69. Right antenna, with sensilla identified by rectangles.