Perdita (Xeromacrotera)

Portman, Zachary M., Griswold, Terry & Pitts, James P., 2016, Association of the female of Perdita (Xeromacrotera) cephalotes (Cresson), and a replacement name for Perdita bohartorum Parker (Hymenoptera: Andrenidae), Zootaxa 4097 (4), pp. 567-574 : 569

Subgenus Xeromacrotera Timberlake, 1954

Type species. Perdita cephalotes ( Cresson, 1878) , ♂, by original designation and monotypy.

Updated subgeneric diagnosis. Xeromacrotera is defined by the following combination of characters: maxillary palpi six-segmented (generally appearing five-segmented due to a minute fifth joint), female with tarsal claws simple, frons shiny with dense deep punctures, and with simple, wavy scopal hairs. Male with bidentate hind tarsal claws and metasoma wider than mesosoma. Xeromacrotera can be separated from the closely-related subgenus Cockerellia , which has the maxillary palpi clearly six-segmented with a normal fifth joint. Xeromacrotera shares many characters with species of Allomacrotera and Procockerellia, which have the maxillary palpi three- or five-segmented. Perdita cephalotes can be distinguished from Allomacrotera and Procockerellia in the male sex by the combination of the bidentate tarsal claws and the broad metasoma, and the female can be distinguished by the shining and heavily punctate face, as well as the wavy rather than corkscrewshaped scopal hairs.

Remarks. Number of palpi. Examination of the 22 specimens of P. cephalotes revealed that both sexes have six maxillary palpi ( Fig. 1 D). Measurements reveal that the maxillary palpi are reduced compared to related Perdita , largely due to the minute size of the fifth joint. The average total length of the maxillary palpi is 0.33 mm (n=12) with the average length of each joint approximately: 100 µm: 50 µm: 50 µm: 50 µm: 15 µm: 60 µm. Length and ratio of the maxillary palpi show no difference between the sexes. In many specimens, the maxillary palpi appear to be five-jointed due to the minuteness of the fifth joint. The fifth joint is particularly difficult to observe in the male, whose yellowish mouthparts lack contrast. Using the typical level of magnification used for specimen identification, most specimens of P. cephalotes would appear five-jointed.

Sex association. Likely due to the unique coloration of the male and the confusion regarding the number of maxillary palpi, the female of P. cephalotes has been described separately under two different names in different subgenera. Collections from the deserts of California, Nevada, and Utah have revealed P. cephalotes to be a relatively common species and allowed confident association of the sexes based on shared collection frequency and the shared characters of the maxillary palpi. When more than one specimen of P. cephalotes has been collected, males and females have been found together at 32 out of 55 unique collection events (at the same date and location). These associated collections have taken place throughout the range of P. cephalotes . The males are strongly associated with the females with only five instances of male P. cephalotes collected without the female. In addition to collection frequency, both sexes share the unique morphological character of shortened maxillary palpi with a minute fifth joint.

With the association of the female, it is now possible to better understand the relationship of Xeromacrotera to other subgenera. The female shares scopal hair morphology with the subgenera Cockerellia and Pentaperdita and it resembles Procockerellia and Allomacrotera in general appearance. However, P. cephalotes is not a match with any of those subgenera; in particular, the six-jointed maxillary palpi separate it from the subgenera Procockerellia, Allomacrotera and Pentaperdita, while the bidentate hind tarsal claws in the male and the presence of a lateral emargination on the fifth sternum of the female separate it from the subgenus Cockerellia ( Danforth 1996) . Due to its unique mix of characters, Xeromacrotera is here retained as a distinct subgenus with the combination of distinguishing characters as outlined above. More work is needed to understand the relationships between these subgenera, though Xeromacrotera may be sister to Procockerellia or Cockerellia .

Figures

FIGURE 1. Perdita cephalotes (Cresson). (A) Small-headed male face. Scale bar = 250 Μm. (B) Large-headed male face. Scale bar = 250 Μm. (C) Female face. Scale bar = 250 Μm. (D) Male maxillary palpi, showing minute fifth palp. Maxillary palpi are similar in both sexes. Scale bar = 100 Μm. (E) Male side view. Scale bar = 1 mm. (F) Female metasoma. Scale bar = 250 Μm. (G) Female lateral view. Scale bar = 1 mm.