Solitary and group nesting in the orchid bee <Emphasis Type="Italic">Euglossa hyacinthina</Emphasis> (Hymenoptera,Apidae)

Summary Orchid bees (Euglossini) provide a potentially informative contrast for examining origins of advanced social behaviour in bees because they are the only tribe in the apine clade that do not form large colonies or have queens and workers. We investigated natural nests of Euglossa hyacinthina Dressler, an orchid bee that nests singly or in groups. By comparing the two types of nests, we examined if individuals in a group merely share the nest (are communal) or exhibit a level of social organization where there is reproductive division of labour among the females. Observations are consistent with communal nesting, indicating that all females in group nests are reproductively similar to the solitary nesting females because the provisioning of young, as well as the ovary development and mating status of females sharing nests were not different than that of solitary-nesting females. Also, multiple female nests did not produce a female-biased brood as predicted for nests with reproductive division of labour. We also investigated potential advantages of group nesting vs. individual nesting. We demonstrate that per capita offspring production is lower in nests with more than one female. However, we found that nests with single females were left unattended for longer periods of time during foraging, and that there was a high incidence of natural enemy attack in nests when females were absent. Group and solitary nesting may be advantageous under different conditions.Received 3 December 2002; revised 7 March 2003; accepted 2 April 2003.