Andrena (Micrandrena) Ashmead 1899

3.1.Andrena(Micrandrena) Ashmead, 1899 Micrandrena Ashmead, 1899: 89. Type species: Micrandrena pacifica Ashmead = Andrena melanochroa Cockerell, 1898, by original designation. Andrenella Hedicke, 1933: 210. Type species: Melitta minutula Kirby, 1802, by original designation. Syn. Lanham 1949: 208. Distandrena Warncke, 1968 a: 60. Type species: Andrena longibarbis Pérez, 1895, by original designation. Syn. Pisanty et al. 2022 a: 12. Fumandrena Warncke, 1975 a: 57. Type species: Andrena fumida Pérez, 1895, by original designation. Syn. Pisanty et al. 2022 a: 12. Proxiandrena Schmid-Egger, 2005: 1030. Type species: Melitta proxima Kirby, 1802 = Andrena proxima, by original designation. Syn. Pisanty et al. 2022 a: 12. Diagnosis. As a unified group, Andrena (Micrandrena) are too morphologically diverse to diagnose with unique defining characters, especially with regard to other members of the highly diverse clade of small-sized Andrena distributed primarily in the Old World (clades 23–24 in Pisanty et al. 2022 a), which includes also Aciandrena, Aenandrena, Fuscandrena, Graecandrena, Parandrenella, and the A. janthina species group. All Micrandrena are relatively small-sized, and all Palaearctic species lack bright facial markings in both sexes. They generally also lack most of the distinct modifications which characterize many other Andrena subgenera, such as elongated mouthparts, enlarged vertex and gena, carinate pronotum, complete propodeal corbicula, sloping profile of propodeum, carinate or toothed hind femur, modified hind tibial spur, plumose scopa, raised area on pygidial plate, or strong male pygidial plate. Beyond these simple generalizations, to provide a clear diagnosis against similar subgenera and species groups, it is necessary to divide Micrandrena into several morphological groups and diagnose each one of them separately, as specified below. As reference groups, the following discussion will focus on the related subgenera Aciandrena (as presently circumscribed), Fuscandrena, Graecandrena and the Andrena janthina group, which are the main taxa most often confused with Micrandrena. For the sake of the present discussion and for utility within the fauna of the Levant and Cyprus, we divide the Palaearctic members of A. (Micrandrena) into the following groups, which to our best understanding, correspond to distinct clades in phylogenomic analysis (Pisanty et al. 2022 a; Bossert et al. in prep.): 1. Andrena longibarbis group – former subgenus Distandrena. 2. Andrena minutula group – this is the old concept of subgenus Micrandrena sensu Warncke in the Palaearctic but excluding the species around A. oedicnema Warncke and A. proxima (Kirby). This group contains the bulk of the species diversity of the subgenus. It corresponds to Schmid-Egger & Scheuchl’s minutula - and nana - groups combined (Schmid-Egger & Scheuchl 1997). We see no justification to distinguish the nana group here, as preliminary molecular data does not support its monophyly, and the minutula / nana group division is not clearly applicable outside Central Europe. 3. Andrena oedicnema group – A. oedicnema Warncke and the closely related A. cedricola Wood. 4. Other unassigned, peculiar taxa, including the well-known Andrena proxima group, here represented by a single species only. The Andrena longibarbis group can be well characterized against other Andrena subgenera by the combination of: 1. A clypeus that is completely flat or almost so, often with longitudinal striations (Fig. 13 E – I); 2. Supraclypeal plate often longitudinally striated; 3. Facial foveae extremely long and narrow, usually extending below the antennal sockets, with the lower ½ – ⅔ almost linear (Fig. 13 D); 4. Propodeal triangle entirely reticulated, essentially lacking any rugae, even basally (Fig. 13 A); 5. Scutum and terga strongly shagreened and impunctate to weakly punctured (Fig. 13 J – P); 6. Hind leg pretarsal claw usually bidentate. This species group is most similar to members of subgenus Aciandrena and the A. janthina species group, but in these reference taxa the clypeus is not always flat, the clypeus and supraclypeal area are never longitudinally striated, the foveae are shorter and more drop-shaped, the body shagreening is usually weaker and finer, and the hind leg pretarsal claw is usually unidentate. The highly diverse Andrena minutula group is more variable morphologically compared to the A. longibarbis group, but it is characterized most of all by a propodeal triangle that is finely but strongly rugose to rugose-areolate, at least on the basal half (Fig. 13 C). Many members of the A. minutula group also have strong integumental sculpturing such as deep punctures or strong shagreening (Figs 15 – 18). Both these traits set this group apart from the related subgenera Aciandrena, Fuscandrena and Graecandrena as well as the A. janthina species group. In these reference groups, the propodeal triangle is more reticulated, with the rugosity absent or weaker and more confined to the basal margin; the integumental sculpturing is generally weaker, with punctures and shagreening usually appearing shallower; and in some species the males have yellow facial markings and / or reduced gonostyli, but these are more difficult to generalize. There are exceptions to most of the above criteria, and caution should be exercised when excluding similar subgenera. Most of the remaining taxa of A. (Micrandrena) in the treatment below can also be diagnosed against other subgenera based on the same criteria mentioned above. Hence, most of the characters of the Andrena minutula group apply also to the A. oedicnema group and to A. proxima; A. extenuata Wood also possesses a similar strongly rugose propodeal triangle. The A. oedicnema group is further characterized by mirror-smooth, mostly impunctate terga (Fig. 14 P), and A. proxima possesses an almost unique, star-shaped wrinkling of the surface of the propodeal corbicula (Fig. 14 M). The three remaining species are more challenging to diagnose, as their propodeal triangles are more weakly or narrowly rugose, as in Graecandrena (Fig. 13 B), however all possess unusual characteristics which are rare among the related subgenera: A. dividicincta Pisanty has very strong tergal hairbands which are strictly limited to the tergal sides (Fig. 14 O); A. pandosa Warncke has broad facial foveae (Fig. 14 K), a protuberant, medially flattened clypeus in which the apicolateral corners are distinctly elevated, and a strongly notched labral process (Fig. 14 B); and A. yelkouan Warncke has an entirely flat clypeus (Fig. 14 A) as well as strongly contrasting dull scutum versus shiny scutellum (Fig. 14 G). It is important to note that several species of the A. minutula group occur in two generations which are morphologically distinct. This includes A. alfkenella Perkins, A. alfkenelloides Warncke, A. chananaea Pisanty & Wood sp. nov., A. minutula, and A. minutuloides Perkins. As a general rule, the second generations possess a smoother cuticle and brighter pubescence (particularly the male facial pubescence), which are most likely adaptations for the warmer ambient temperature and stronger solar radiation associated with late season (Ostwald et al. 2025). Bionomics. Most of the bionomic data on Micrandrena species has been gathered from studying Central European taxa, especially the work of Westrich (1989). Recently, Wood (2023 a, b) has conducted pollen analyses on several west Mediterranean species, thus broadening the spectrum of studied taxa. Far less is known about most of the Levantine taxa included in this study, as well as those from the Nearctic and East Palaearctic realms. Altogether, detailed pollen preference data is publicly available for ca. 40 species of Micrandrena, showing distinct trends among different species groups within the subgenus. All members of the Andrena longibarbis species group appear to exhibit a high affinity for Brassicaceae, and all six species with analysed pollen loads are strict Brassicaceae specialists (Westrich 1989; Dermane et al. 2021; Wood 2023 a, b); we assume that similar specialization exists in all other members of this group. By contrast, the Andrena minutula group, the most diverse group within the subgenus, exhibits a high proportion (ca. 70 %) of pollen generalists, with Brassicaceae and Apiaceae as the most common host plants (Westrich 1989; Scheuchl & Willner 2016; Wood 2023 a, b). As expected, voltinism tends to correlate with pollen host breadth within this group, i. e. pollen generalist species have a greater tendency to fly in two generations per year, greatly extending their foraging season (Westrich 1989; Scheuchl & Willner 2016). Other species of Micrandrena outside these two groups exhibit diverse pollen preferences, including specialists of Apiaceae, Asteraceae, Cistaceae, Resedaceae and Salicaceae, as well as generalists (Westrich 1989; Larkin et al. 2008; Scheuchl & Willner 2016; Wood & Roberts 2018; Pisanty et al. 2022 b; Wood 2023 a, b; unpublished data). In terms of biogeography, the highly diverse Andrena minutula group is common in temperate and Mediterranean biomes throughout the Palaearctic, with numerous species confined to higher elevations. The Andrena oedicnema group is associated with similar habitats, with a much more limited distribution. On the other hand, the A. longibarbis group is strongly associated with dry habitats in the Western Palaearctic, and is most diverse around the southern Mediterranean Basin and the Iberian Peninsula.

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