Dialictus

Gibbs, Jason, 2010, Revision of the metallic species of Lasioglossum (Dialictus) in Canada (Hymenoptera, Halictidae, Halictini) 2591, Zootaxa 2591 (1), pp. 1-382 : 11-12

Diagnosis of Dialictus

Dialictus are small (approximately 3.4–8.1 mm), andreniform bees with dull metallic reflections at least on the head and mesosoma in most species, a strongly arched basal or posterior portion of the basal vein, and weakened distal veins of the fore wing, especially 1rs-m, 2rs-m, 2m-cu and the distal abscissa of M ( Fig. 2 ). Dialictus are recognisable as halictids by the lacinia that extends high up the anterior surface of the labiomaxillary tube ( Michener 2007). Several characters typical of the subfamily Halictinae are evident in Dialictus including: distinct episternal groove extending below the level of the scrobe, and, in females of nest-building species, a strong apical process of the labrum with a distinct dorsal keel ( Fig. 3A ) and a specialized longitudinal median area dividing the prepygidial fimbria. The weakened distal veins of the forewing are diagnostic of the subtribe Gastrohalictina (Pesenko 1999) (= Lasioglossum s.l.). The weakened or absent vein 1rs-m distinguishes Dialictus from Lasioglossum s.s., all the North American species of which (except L. (L.) pavonotum (Cockerell)) lack metallic reflections. Species of Halictus (Seladonia) are of similar size and colouration as Dialictus but have strong distal veins on the forewing and distinct apical fasciae on the metasomal terga.

The subgenus Evylaeus (= “carinate” Evylaeus ; see Michener 2007) cannot be clearly distinguished from Dialictus . Evylaeus has weakened venation similar to Dialictus . Members of both subgenera commonly have small gonostyli and a distinct retrorse lobe. Evylaeus typically lack metallic colouration (but see Ebmer 1969; Pesenko 2007; Gibbs & Packer in prep.) and have a strong lateral carina of the propodeum usually meeting a strong transversely oriented carina which at least partially separates the dorsal and posterior surfaces of the propodeum. The propodeum of Dialictus with black integument generally does not have a lateral carina that reaches the dorsal margin and if so usually doesn’t have the dorsal and posterior surfaces delimited by a transversely oriented carina. In some cases, such as L. (D.) pectorale (Smith) , black Dialictus species have stronger propodeal carinae than do carinate Evylaeus . The inner metatibial spur of Dialictus females is pectinate with at least 2 or 3 large teeth. In contrast, the inner metatibial spur of Evylaeus females is usually serrate or if pectinate then the teeth are short.

Two possibly synonymous subgenera, Hemihalictus and Sudila , each with priority over Dialictus can be distinguished as follows. The subgenus Hemihalictus is black in colour, lacks vein 1rs-m (only a few species of Dialictus lack this vein) and the female has a serrate inner metatibial spur whereas in Dialictus females the spur is pectinate. The Asian subgenus Sudila is larger (10–11 mm) and has a distinct tubercle on the lower mesepisternum that is absent in Dialictus .

Figures

FIGURE 2. Forewings of female Lasioglossum subgenus Dialictus. (A) Typical forewing with three submarginal cells. Pterostigma (pt), basal vein (b), arrows indicate weakened veins. (B) Forewing with two submarginal cells. Arrows indicate weakened veins.

FIGURE 3. Labrum of female Dialictus; (A) nest-building species, (B) parasitic species. Arrows indicate apical process.