Agapostemon Guérin-Méneville, 1844

Portman, Zachary M., Arduser, Mike, Powley, Mary E. & Cariveau, Daniel P., 2024, Taxonomy of Agapostemon angelicus and the A. texanus species complex (Hymenoptera, Halictidae) in the United States, European Journal of Taxonomy 958, pp. 203-241 : 206-207

Genus Agapostemon Guérin-Méneville, 1844

Keys to “doubly punctate” species of Agapostemon of the United States

Females can be recognized from other US Agapostemon species by the doubly-punctate scutum, which contains intermixed punctures of two distinct sizes. Males lack the doubly-punctate scutum, but can be recognized by the following combination of characters: hind femur only moderately enlarged with a ventral tooth present, S4 with swelling that reaches the posterior edge of the segment laterally, and a longer F1 that is ⅔ to ¾ the length of F2 (as opposed to half or less the length of F2). Both sexes of the “doubly punctate” species key out to A. texanus in Mitchell (1960) and both sexes key out to either A. angelicus or A. texanus in Roberts (1972) and Portman et al. (2022).

Key to females

Note that A. angelicus and A. subtilior are quite variable species, and though the characters listed here are mostly consistent, sometimes they vary. In the key, the word “generally” is used to indicate characters that work in about 90% of specimens.

1. Genal striations in hypostomal area exceptionally coarse and deep, with valleys between the ventral ridges so deep and irregular that it is difficult to see the bottom, with 5–7 large straight striae heading towards and ending along the longitudinal part of the hypostomal carina ( Fig. 1C–D )................................................................................................. A. texanus Cresson, 1872

– Genal striations fine ( Fig. 1A ) to moderately coarse ( Fig. 1B ); genal striations generally curving away from or parallel to the longitudinal part of the hypostoma and towards the lateral part of the hypostomal carina ( Fig. 1A–B ) ......................................................................................................... 2

2. Clypeus flatter, distinctly flat all the way to the apical margin, with the apical margin present as a very narrow vertical overhang (just above the apical fimbriae), forming a weak but distinct complete carina ( Fig. 2A–B ); dorsal propodeal sculpturing moderately coarse ( Fig. 3A ); pleural reticulations more strongly carinate, even posteriorly ( Fig. 3C ); metasoma with denser punctures ( Fig. 4A ), punctures on T1 generally contiguous (separated by less than one puncture width), even on lateral areas basal to premarginal line ( Fig. 4D red arrow)............................. A. angelicus Cockerell, 1924

– Clypeus more convex, apical margin without a very narrow vertical portion, instead more evenly curving onto the base of the apical fimbriae ( Fig. 2C–D ); dorsal propodeum with sculpturing generally weaker, ranging from delicate to somewhat coarse ( Fig. 3B ), and if coarser, then typically strongly anastomizing; pleural reticulations more weakly carinate, especially posteriorly ( Fig. 3D ); metasoma with sparser punctures ( Fig. 4B ), punctures on T1 generally with distinct interspaces, with punctures in some areas separated by greater than one puncture width, especially laterally, just basal of the premarginal line ( Fig. 4E red arrow)................................... A. subtilior Cockerell, 1898

Key to males

Note that we rely on color of the hind tibia because it is easy and convenient, but given the color variation seen in males, it would not be surprising to find males that break the color rules, and structure should always be given precedence.

1. Hind tibia with extensive dark mark ONLY on posterior face ( Fig. 5A–B ; anterior face with no dark mark, though there may be a dark spot at the apex as in Fig. 5A ); hind femur and tibia relatively less inflated ( Fig. 5A ); hind basitarsus relatively narrow ( Fig. 5K ); genitalia with basal stylus thickened and a relatively small medial plate that is broader than long ( Fig. 6A )............................................... .............................................................................................................. A. angelicus Cockerell, 1924

– Hind tibia never with dark mark only on posterior face, can have dark marks on both anterior and posterior face ( Fig. 5E–F and Fig. 5G–H and Fig. 5I–J ), no dark marks on either side ( Fig. 5C–D ), or a dark mark only anteriorly (similar to Fig. 5E ); hind femur and tibia relatively larger ( Fig. 5E, I ); hind basitarsus not as narrow ( Fig. 5L–M ); genitalia with basal stylus slender and tapering, and medial plate relatively large and roughly as long as broad ( Fig. 6B–C ) ........................................... 2

2. Hind tibia with posterior face with large black mark ( Fig. 5J ), taking up most of the tibia and generally more or less narrowly attenuated in the basal half; genitalia with basal stylus shorter and more evenly curved ( Fig. 6C–D ); hind tarsus with second tarsomere shorter and more completely fused to basitarsus, with transition between them less obvious ( Fig. 5M ). A. texanus Cresson, 1872

– Hind tibia posterior face with dark mark smaller, not taking up most of tibia ( Fig. 5F, H ) or sometimes absent ( Fig. 5D ), and if the dark mark is larger, it is limited to the apical half of the tibia and generally abruptly cut off rather than narrowly attenuated ( Fig. 5H ); genitalia with basal stylus longer and straighter basally, more abruptly upturned towards apex ( Fig. 6B, E ); hind tarsus with second tarsomere longer and less completely fused to basitarsus, with transition between them quite obvious ( Fig. 5L ) .................................................................................... A. subtilior Cockerell, 1898

Figures

Fig. 1. Genal striae of females. A. Agapostemon angelicus Cockerell, 1924. B. A. subtilior Cockerell, 1898. C. A. texanusCresson, 1872 s. s. D. Zoomed-in view ofA. texanuss. s. striae, image of paralectotype (MCZENT548), provided by Zoe Flores and Crystal Maier of the MCZ. Scale bars: 1 mm.

Fig. 2. Comparison of Agapostemon angelicus Cockerell, 1924 and A. subtilior Cockerell, 1898, female head and clypeus. A. A. angelicus, face. B. A. angelicus, apex of clypeus. C. A. subtilior, face. D. A. subtilior, apex of clypeus. Scale bars: A, C = 1 mm; B, D = 500 µm.

Fig. 3. Thorax of Agapostemon angelicus Cockerell, 1924 and A. subtilior Cockerell, 1898, females. A. A. angelicus, propodeum. B. A. subtilior, propodeum. C. A. angelicus, side. D. A. subtilior, side. Scale bars: 1 mm.

Fig. 4. Female metasoma comparison. A. Agapostemon angelicus Cockerell, 1924. B. A. subtilior Cockerell, 1898. C. A. texanus Cresson, 1872 s. s. D. A. angelicus, T1 and T2, with red arrow pointing to lateral areas basal to premarginal line with denser punctures. E. A. subtilior, T1 and T2, with red arrow pointing to area of sparser punctures. F. A. texanus s. s., T1 and T2, with red arrow pointing to area of denser punctures. Scale bars: 1 mm.

Fig. 5. Male hind legs. A. Agapostemon angelicus Cockerell, 1924, anterior view. B. A. angelicus, posterior view. C. A. subtilior Cockerell, 1898, lightest color, anterior view. D. A. subtilior, lightest color, posterior view. E. A. subtilior, anterior view. F. A. subtilior, posterior view. G. A. subtilior, dark, anterior view. H. A. subtilior, dark, posterior view. I. A. texanus Cresson, 1872, anterior view. J. A. texanus, posterior view. K. A. angelicus, basitarsus. L. A. subtilior, basitarsus. M. A. texanus, basitarsus. Scale bars: A–J = 1 mm; K–M = 500 µm.

Fig. 6. Apical view of male genitalia. A. Agapostemon angelicus Cockerell, 1924. B. A. subtilior Cockerell, 1898. C. A. texanus Cresson, 1872 s. s. D. A. texanus s. s., zoomed in with black arrow pointing to more evenly curved lower stylus. E. A. subtilior zoomed in with black arrow pointing to more laterally extending lower stylus. Scale bars: 500 µm.