A Classification of Nest Architecture of Bees in the Tribe Augochlorini (Hymenoptera: Halictidae; Halictinae), with Description of a Brazilian Nest of Rhinocorynura inflaticeps

Abstract

A nest of Rhinocorynura inflaticeps, a rare Brazilian halictine bee, is described for the first time. The main burrow ends in a cavity in which the brood cells are clustered. No blind burrow issues from the cavity. The cell cluster is brittle and supported by pillars. The vertical cells are not closely spaced. In general appearance the nest resembles those of Pseudaugochloropsis and Neocorynura. Known nest types of Augochlorini are reclassified using arrangement and orientation of cells and presence or absence of lateroid burrows. Compared with those of Halictini, nests of Augochlorini are generally more specialized by absence of laterals, frequent appearance of clustered cells, and frequent vertical orientation of cells. A cladistic analysis of augochlorine nest types suggests the parallel evolution of two types of cluster nests, one with thickwalled clusters of predominantly vertical cells and one with thin-walled clusters of horizontal or tilted cells, and a secondary evolution of the supposedly primitive unclustered cells of Augochlora (Oxystoglossella). Nest types suggest that Paroxystoglossa and Augochlorodes were incorrectly placed in generic groups based on adult morphology. THE NUMEROUS SPECIES of augochlorine bees are important components of the Neotropical insect fauna. These frequently brilliant-green bees' visit a wide variety of flowers and are common in forested and open habitats from the coastal lowlands to the high Andes. In contrast to the cosmopolitan Halictini, the Augochlorini occur only in the Western Hemisphere and are most abundant and diverse in the Neotropical region, where Eickwort (1969a) recognized 24 genera. Only a few species of Augochlora, Augochlorella, and Augochloropsis occur widely in the United States and Canada. Biological studies of the halictine bees have stressed social behavior (reviewed in Michener 1974) and nest architecture. Most sweat bees make nests in the soil, although some species nest in dead wood. The most primitive type of halictine soil nest (fig. 8) (Sakagami and Michener 1962) consists of a main burrow that extends into the soil from the entrance and may be branched. Each cell is at the end of a long to short lateral burrow that connects it to the main burrow or one of its branches; this lateral is narrower than the main burrow. The cell is lined with a waterproof glandular secretion and is provided with a soft provision-mass of pollen and dilute honey. One egg is laid on top of the mass of provision, and the cell is then sealed by filling the lateral with soil. The main burrow terminates as. a blind burrow beyond the last cell in the nest. In some halictine nests, cells may be arranged end-to-end in series along a lateral, forming parodalous nests, while in others, the laterals may be very short and virtually absent. Each cell opens directly onto a burrow and is sealed with a thin closure of soil after oviposition. In some nests the cells may be clustered at one point of the burrow, and the cluster may be surrounded by a cavity that more or less isolates it from the surrounding soil except for some supporting pillars (figs. 1, 3). Cells in such clusters are commonly oriented in the same direction, forming a comb (fig. 3). The cell cluster or its surrounding cavity usually directly meets the burrow, but sometimes a lateroid burrow connects it to the main or