Lasioglossum (Dialictus) cressonii (Robertson)

Gibbs, Jason, 2011, Revision of the metallic Lasioglossum (Dialictus) of eastern North America (Hymenoptera: Halictidae: Halictini), Zootaxa 3073, pp. 1-216 : 79-80

Lasioglossum (Dialictus) cressonii (Robertson)

Halictus Cressonii Robertson, 1890: 317 . Ƥ 3.

Lectotype. Ƥ USA, Massachusetts [ANSP: 4253] designated herein. Examined. Dialictus delectatus Mitchell, 1960: 435 . 3.

Holotype. 3 USA, Maryland, Plummer’s Is., 13.ix.1958 (K.V. Krombein); [ NMNH: 66072). Examined. Halictus (Chloralictus) cressoni Viereck, 1916: 707 (emend.).

Taxonomy. Robertson, 1902b: Chloralictus Cressonii , p. 249 (key); Michener, 1951: Lasioglossum (Chloralictus) cressonii , p. 1113 (catalogue); Mitchell, 1960: Dialictus cressonii Ƥ3, p.390 (redescription, key); Krombein, 1967: Lasioglossum (Dialictus) cressonii , p. 463, L. (D.) delectatum , p. 463 (catalogue); Hurd, 1979: Dialictus cressonii , p. 1965, D. delectatus , p. 1965 (catalogue); Moure & Hurd, 1987: Dialictus cressonii , p. 97, D. delectatus , p. 99 (catalogue); Gibbs, 2010b: Lasioglossum (Dialictus) cressonii Ƥ3, p. 101 (redescription, key, synonymy).

Diagnosis. Female L. cressonii are recognisable by the following diagnostic combination: head and mesosoma golden green; hypostomal carinae parallel, unreflexed; mesoscutal punctures very coarse, moderately dense between parapsidal lines (i=1=1.5d) ( Fig. 4 B); mesepisternum very coarsely rugose; propodeal carinae strong, lateral carina reaching dorsal surface ( Fig. 2 A); and metapostnotum with posterior margin sharply angled. They are easily distinguished from L. bruneri and L. reticulatum , which have divergent hypostomal carinae. Female L. albipenne have relatively sparse mesoscutal punctures (i=1–3d) and noticeably pale wings. Female L. nymphaearum have hypostomal carinae reflexed distally and metapostnotum with posterior carina uninterrupted.

Male L. cressonii are similar to females but may be further recognised by clypeal hairs not obscuring surface, flagellomeres elongate (length/width ratio = 1.69–1.83), and mesoscutum with anterior margin punctate. They are most similar to male L. bruneri and L. reticulatum which both have anterior margin of mesoscutum rugose and clypeal hairs denser.

Range. Nova Scotia west to British Columbia, Washington, south to Georgia and Colorado. USA: CO, CT, GA, IA, ID, IL, IN, KY, MA, MD, ME, MI, MN, MO, NC, NH, NJ, NY, PA, UT, VA, VT, WI, WV. CANADA: AB, BC, ON, NB, NS, PE, PQ.

DNA Barcode. Available. Multiple haplotypes.

Comments. Common.

Lasioglossum cressonii is known to nest in rotten wood ( Mitchell 1960).

DNA barcodes of L. cressonii show levels of genetic divergence suggestive of multiple species (J. Gibbs unpublished data). Morphological examination has not corroborated the existence of additional species. Additional study is required before any new species in this possible complex can be described.

The specimen indicated above is designated herein as the lectotype to ensure stability in the application of the name. A specimen of L. achilleae also occurs in the syntype series, which could potentially lead to confusion.

Figures

FIGURE 2. Propodeum and metapostnotum variation in female Lasioglossum (Dialictus). (A) L. cressonii, (B) L. nigroviride, (C) L. lineatulum, (D) L. coreopsis, (E) L. connexum, (F) L. (D.) sp.

FIGURE 4. Mesoscutum of female Lasioglossum (Dialictus) showing sculpture and punctation variation. (A) L. reticulatum, (B) L. cressonii, (C), L. nymphaearum, (D). L. (D.) sp., (E) L. heterognathum, (F) L. coreopsis, (G) L. pilosum, (H) L. nigroviride, (I) L. lineatulum.