Abstract
The present study consists of the life history and behavior of a primitively social halictine bee Lasioglossum umbripenne. The work was conducted 15 km north of Quepos (200 meters altitude) on the southern Pacific coast of Costa Rica. The bees are active only during the dry season, January through April. The colonies contain well established worker and reproductive castes, the queen being easily differentiated from the others by her larger size. Cells destined to produce queens differ from those that produce workers and males in the size and shape of the food mass and in cell dimensions. The nests are burrows in the ground, normally with only one queen.
In founding the nest, the queen digs a burrow 8 to 15 cm deep and constructs from one to six cells, one each night, which she provisions the follow ing morning. Provisioning requires five pollen collecting trips. An egg is laid upon the mass, now in the form of a small sphere, and the cell is then dosed. The queen keeps the entrance of the nest well sealed with soil at all times except in the morning when she is working or feeding. After preparing and provisioning all the cells, she ceases her activities and waits until the progeny reach maturity. The development from egg to adult requires 22 days and the progeny emerge mostly as workers. From this time on, the nest is continually active and the workers deepen the nest and provision other cells while the queen provides each with an egg. Many workers can also lay eggs; in fact, almost 50 per cent of the population showed ovarian development. Occasionally fertilized workers are also found. The flight range of these bees is a cirde of about 100 meters around their nests.
From January through April the nests become progressively deeper and more complicated, with additional branching and looping. The bee population and the number of cells likewise increase from month to month.
The queen generally lives one year, the workers about a month, and the males less then two weeks. During the months of activity of the colony the queen is never replaced. She lays an egg a day (rarely two). Males are produced throughout the existence of the colony, but an appreciable number was never observed except at the end of April. This peak in the male popula tion is correlated with the production of new queens and marks the end of the colony's existence. The new queens soon mate with the males and then leave the nesting area. Meanwhile all the workers and males die and the nests are abandoned. Not until the beginning of the dry season will the new fertilized queens reappear to begin another cycle.