Dialictus

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 View FIGURE 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 View FIGURE 3 ) 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 .