Evidence for social nesting in neotropical ceratinine bees

Small carpenter bees (Ceratinini) are a key taxon to understanding the transition from subsocial to social behaviour, as all documented groups are long-lived and tend to their young periodically throughout development, though the behaviour of multiple lineages is little known. This study provides the first evidence for social nesting in three Neotropical species of Ceratina (Ceratinula) from Panama. Social nesting was associated with nest reuse, consistent with the hypothesis of kin associations, and the proportion of nests (per species) that displayed sociality was as follows: C. buscki 5 %; C. rectangulifera 0 %; C. tricolor 6 %; and C. zeteki 23 %. Sociality is always a low-frequency phenomenon in ceratinine bee populations, and generally represents a third or less of the population. The fact that the majority of colonies remain solitary indicates that solitary nesting is adaptive in the studied species.