Lasioglossum (Dialictus) plumbeum (Ashmead 1900)

Figs 14, 15, 16

Halictus plumbeus Ashmead (1900: 218, 220). Saint Vincent. Syntype males and females (NHMUK, USNM; Fig. 14). Examined.

Halictus plumbeus: Ashmead (1900: 304) checklist; Friese (1909: 37) catalogue; Cockerell (1915: 9) taxonomic note; Cockerell (1938: 280, 281) taxonomic notes.

Halictus (Chloralictus) plumbeus: Sandhouse (1924: 4) identification key; Cockerell (1937: 113) taxonomic notes.

Dialictus plumbeus: Moure and Hurd (1987: 124) catalogue; Moure (2007: 853) catalogue.

Lasioglossum plumbeum: Gibbs (2016: 6, 15) taxonomic notes.

Material examined.

SVG • Saint Vincent • St. Vincent, leg. H.H. Smith ( Halictus plumbeus syntypes 1 ♀ NHMUK, 1 ♀ USNM) • St. Vincent (Windward side), leg. H.H. Smith (2 ♀ USNM) • Charlotte Parish • Belair Mespo Peruvian Vale Rd., 13.173417 -61.151111, 71 m, 13.V.2016, leg. Miklasevskaja and Ferrari (1 ♂ WRME) • Fancy, 1 km S of Windward hwy. 13.380122 -61.170588, 55 m, 18.V.2016, leg. Miklasevskaja and Ferrari (1 ♂ WRME) • Greiggs, Charlotte Mtn., 13.222417 -61.173361, 478 m, 14.V.2016 , leg. Miklasevskaja and Ferrari (1 ♂ WRME) • St. Andrew Parish • Vermont Trail Rd., 13.201639 -61.241333, 114 m, 15.V.2016, leg. Miklasevskaja and Ferrari (1 ♀ WRME) • St. David Parish • Cumberland Way, 19.IX.1991, leg. R.E. Woodruff, near beach (1 ♀ 1 ♂ FSCA) • Wallilabou, 14.X.1991, leg. R.E. Woodruff, day catch (10 ♀ 2 ♂) • St. George Parish • Cane Hall, 22.IX.1991, leg. R.E. Woodruff, sweeping (4 ♀ 9 ♂ FSCA) • Cane Hall, Rick’s Apts., 17.IX.1991, leg. R.E. Woodruff, vacant lot (1 ♀ FSCA) • Rivulet Agr. Sta. 10-15.X.1991, leg. R.E. Woodruff, Malaise trap (3 ♀ FSCA); 27-30.IX.1991, leg. R.E. Woodruff, Malaise trap (1 ♀ 1 ♂ FSCA) • Majorca Mts., Riley Rd., 13.180694 -61.193556, 366 m, 13.V.2016 , leg. Miklasevskaja and Ferrari (1 ♀ WRME) • St. Patrick Parish • Cumberland Valley, 17, VI.1977, leg. E.E. Grissell (11 ♀ 21 ♂ FSCA) • Hermitage Forestry Cottage, 11-13.X.1991, leg. R.E. Woodruff, day catch (2 ♀ 1 ♂ FSCA) • Rutland Vale, 1 km N on Leeward Hwy., 13.218727 -61.270954, 60 m, 19.V.2016, leg. Miklasevskaja and Ferrari (1 ♀ WRME) • Grenadines • Bequia, Industry, 24.IX.1991, leg. R.E. Woodruff (1 ♂ FSCA) .

Notes.

Lasioglossum sanctivincenti is quite similar to L. plumbeum . The most striking difference is the darker blue colour of the head and mesosoma of L. plumbeum . Lasioglossum sanctivincenti has a shorter head (face length/head width ratio = 0.82 SD 0.02) than L. plumbeum (0.86 SD 0.01). Mesoscutal puncture density is subtly different between the two species. In L. sanctivincenti punctures laterad of the parapsidal line are dense, but distinctly separated. These are nearly reticulate in L. plumbeum, without clear interspaces. Immediately mesad of the parapsidal line, L. sanctivincenti has distinctly separated punctures (IS ≤ 1 PD), but these are denser in L. plumbeum (IS ≤ 0.5 PD). Ashmead’s (1900) original measurements suggest that L. santivincenti is larger (4-5.5 mm) than L. plumbeum (3.5-4.5 mm). In Sandhouse’s (1924) key, they separate at couplet 43 based on size and Cockerell (1938) also refers to the smaller size of L. plumbeum . However, this may be an artefact of H.H. Smith’s original sample as more recently collected specimens of L. plumbeum include a large size range (> 5 mm) overlapping with that of L. sanctivincenti . The size variation in L. plumbeum may be an indication of weakly defined social castes in L. plumbeum, which is a common feature of eusocial halictines (Michener 1990).