The story begins with the classification of the so-called paracolletine bees, a lineage within the family Colletidae, the plasterer bees, whose members line their nest burrows with a cellophane-like waterproof secretion. Within the subfamily Neopasiphaeinae, which is concentrated in Australia, the 2022 treatment by Engel and Gonzalez recognized several new subtribes and genera, drawing loosely on a molecular phylogeny published by Almeida and colleagues in 2019. For the Australian region, three subtribes of the tribe Neopasiphaeini were recorded: Baeocolletina, Neopasiphaeina, and Phenacolletina. Most of the genera recognized in that treatment had previously been treated as subgenera of Leioproctus, a genus so species-rich and morphologically varied that its internal classification has been contested for decades. Phenacolletina, by contrast, was proposed for a single distinctive genus, Phenacolletes.

Baeocolletina was created for the genus Baeocolletes, originally described by Charles Michener in 1965 as a subgenus of Leioproctus and generally recognized as such ever since. Baeocolletes is indeed a distinctive insect. Its members possess two submarginal cells in the fore wing, with the first recurrent vein entering the first submarginal cell basal to the first submarginal cross vein, an arrangement that separates it from most relatives, in which the first recurrent vein terminates at the second submarginal cell. Packercolletes, proposed for Leioproctus idiotropoptera, was shuffled into the same subtribe based entirely on this single feature of wing venation: the first recurrent vein of the new genus also reached the first submarginal cell at or slightly basal to the submarginal cross vein. Crucially, the authors themselves flagged this placement as tentative, and no phylogenetic analysis was offered in support of it.

That single-character justification has not aged well. The classification of neopasiphaeine bees proposed in 2022 has attracted criticism at the family-group level, most notably from Brazilian taxonomist Fernando Melo, and several of the genus-group names proposed in that work have since been synonymized within Leioproctus by other researchers. The deeper problem is one that taxonomists confront constantly: a classification built on one or two morphological characters can collapse the moment those characters are re-examined across a broader sample of species. This is precisely what happened with the diagnostic features used to place Packer’s bee.

Leioproctus idiotropoptera is, by any standard, a strange animal. When Lance Packer described it in 2006, he noted its long jugal lobe, a lobe at the rear margin of the hind wing that suggested an alliance with the subgenus Leioproctus (Colletellus), also established by Michener in 1965. But the species lacked the ciliate inner hind tibial spur that had been defined as a hallmark of Colletellus, and working through the available keys led instead to the subgenera Filiglossa or Euryglossidia, neither of which possesses an elongate jugal lobe. Compounding the confusion, the single known male bore extraordinary fore wing venation: the second recurrent vein was deeply concave, pinching the second medial cell into a narrow waist, and the two recurrent veins were separated by only a few vein widths. The female’s venation, by contrast, looked fairly typical for a Leioproctus with two submarginal cells. The species remained unplaced in the major 2013 revision of Australian Leioproctus by Gwen Maynard.

The resolution hinges on a 2018 revision of Colletellus by Remko Leijs and colleagues, which described numerous new species and, in doing so, substantially broadened the concept of the subgenus. That work demonstrated that the ciliate inner hind tibial spur, long used in combination with the long jugal lobe to define Colletellus, is not always diagnostic. Leijs and colleagues provided a revised diagnosis that also accommodated variable fore wing venation and a large, parallel-sided stigma, the thickened darkened area near the leading edge of the wing. Both of these features apply to Packer’s enigmatic species. Moreover, Leijs and colleagues highlighted a convex clypeus and supraclypeal area, the facial sclerites below and between the antennal bases, as characteristic of Colletellus; these same features were used by Engel and Gonzalez in 2022 both in their key to Australian neopasiphaeine genera and in their diagnosis of Packercolletes, where they distinguished it from Baeocolletes, whose clypeus and supraclypeal area are flattened. The very characters used to define Packercolletes as a genus turn out to be standard equipment within Colletellus.

The wing veins tell a similarly accommodating story. Although all but one of the Colletellus species recognized in 2018 have two submarginal cells, members of the subgenus show considerable variation in venation, and some species have the first recurrent vein meeting the first submarginal cross vein, mirroring the condition that once seemed so exceptional in Leioproctus idiotropoptera. Under the revised, evidence-based concept of Colletellus, Packer’s species fits comfortably, if eccentrically, within its bounds. The new note accordingly proposes that Packercolletes Engel, 2022 be treated as a junior synonym of Leioproctus (Colletellus) Michener, 1965, a formal act of nomenclatural housekeeping that eliminates a genus erected on thin evidence.

None of this means the species has lost its intrigue. Leioproctus idiotropoptera remains known from only three specimens, all collected in 1998, and the single known male displays modified fore wings and unusual structures on the fore and mid legs, a detail worth noting because the 2022 treatment misreported them as mid and hind leg modifications. Such exaggerated structures are not found in other Colletellus species, at least not to the same extent. Yet modified legs occur in other subgenera of Leioproctus, as do modified antennae, so even these flamboyant features are not unprecedented within the genus in its broad sense. Rarity, in other words, is not evidence of deep distinctiveness, a lesson that recurs throughout taxonomy whenever a single specimen becomes the sole ambassador for a lineage.

The author of the new note points to a path forward that extends beyond morphology. DNA could likely be extracted from the three existing specimens to test whether the species truly nests within Colletellus, as now proposed, or whether it warrants recognition as a distinct subgenus, for which the name Packercolletes would remain available should evidence demand it. The prospects for such a test are reasonable: many of the Colletellus species described in 2018 have COI barcode sequences deposited in the Barcode of Life Data System, and the 2019 molecular phylogeny that underpins much of the current higher classification already included sequences from other Leioproctus subgenera and other neopasiphaeines. Genomic data from the holotype and its companions could settle the question decisively, though whether museum curators would sanction destructive sampling of type material from a species unseen for nearly three decades is another matter.

There is also a nomenclatural wrinkle that illustrates how classification decisions ripple through the names organisms carry. Michener in 1965 proposed Leioproctus velutinellus as a replacement name for Andrenopsis velutinus Cockerell, 1929, which had turned out to be a junior homonym of an earlier name, Paracolletes velutinus Cockerell, 1929. Under Engel and Gonzalez’s 2022 classification, transferring the type species of Colletellus to the genus Colletellus would have restored Cockerell’s original name for it. Under the classification followed in the new note, which keeps Colletellus as a subgenus of Leioproctus, the replacement name Leioproctus velutinellus remains the correct combination. As Melo observed in 2022, there is still much to resolve in Neopasiphaeinae, and the case of Leioproctus idiotropoptera is a vivid reminder that in bee systematics, every rank, every character, and every name is only as strong as the evidence beneath it.

Subject of Research: Taxonomic placement of the Australian bee Leioproctus idiotropoptera within the subgenus Leioproctus (Colletellus)

Article Title: A note on the subgeneric placement of Leioproctus idiotropoptera Packer, 2006 ( Hymenoptera , Colletidae , Neopasiphaeinae )

Article References: A note on the subgeneric placement of Leioproctus idiotropoptera Packer, 2006 ( Hymenoptera , Colletidae , Neopasiphaeinae ). (n.d.). https://doi.org/10.3897/jhr.99.211445

Image Credits: AI Generated

DOI: 10.3897/jhr.99.211445

Keywords: taxonomy, bees, Leioproctus, Colletidae, Neopasiphaeinae, Colletellus, Packercolletes, Australia, Hymenoptera, wing venation, systematics, synonymy