Abstract
This paper consists of descriptions of the life cycle and nest structure of the two known species of Costa Rican bees of the genus Halictus (subgenus Seladonia), H. hespeterus and H. lutescens. All observations were made in the lowland parts of the province of Guanacaste, Costa Rica, which has a dry season froro mid-December to May. Although our observations on H. hesperus were largely carried out in the dry season and on H. lutescens entirely in the wet season, the life histories of the two species are presumably similar. Activity is largely in the dry season, with large colonies containing many workers and probably with extensive male and gyne production late in the dry season. The wet season is seemingly passed in a state of ovarian diapause in the nests, the bees making occassional feeding trips and excavating lateral burrows, however, at least in the case of H. lutescens.
The four known neotropical species of Halictus are distinguished in a taxonomic section and the distributions of the two Middle American species of the subgenus Seladonia are mapped.