BIOLOGY OF THE STINGLESS BEE PLEBEIA-REMOTA (HOLMBERG) - OBSERVATIONSAND EVOLUTIONARY IMPLICATIONS

The genus Plebeia has a special significance for the study of social e volution of stingless bees: morphologically primitive, its species dis play a wealth of behavioural evolution, especially with respect to the oviposition process. We compare Plebeia remota with the few other mem bers of the genus studied so far. Related to its subtropical geographi cal range, brood production is seasonal (there is no brood in the colo ny in colder months), and adult workers occur as summer and winter bee s. The nest is in tree cavities, and the involucrum is absent or restr icted to the winter period. Brood cells are arranged in horizontal com bs, and new cells are built completely synchronously. Each series cons ists of up to 50 cells, their number being mainly dependent on colony size. Construction speed is remarkably constant, allowing 4-6 batches per 24 hours. Cell building and provisioning are activities of a small group of specialized workers. The oviposition cycle follows the class ical subdivisions for stingless bees. During the patrolling phase a wo rker may ''offer'' a trophic egg in a most remarkable way: while retre ating backward from the queen she bends the abdomen under thorax and h ead, and lays an egg on the comb. This egg is eaten by the queen or a worker. The provisioning, oviposition and operculation of all cells oc cur simultaneously, each cell is provisioned by 4-9 workers. Localizat ion of a cell by the queen may be facilitated by its characteristic gu ard, which ''defends'' the cell against the approaching queen. The deg ree of synchronization within a batch is very high: the duration per c ell lasts 420-950 sec, the batch of up till 50 cells needs only 557-11 60 sec. Operculation is done by a worker that was not involved in the previous steps. Males are generally produced by the queen. Several mal e producing cycles per year occur. In orphan colonies laying workers g ive rise to males, and in queenright colonies workers may occasionally reproduce as well. Division of labour follows the general pattern for stingless bees; however, cell building and provisioning are activitie s of a specialized group of workers.