Queen turnover, nest usurpation and colony mortality in wild nests of the stingless bees Tetragonula carbonaria and Tetragonula hockingsi (Hymenoptera: Apidae)

Social bees of the tribe Meliponini (stingless bees) are used as managed pollinators of crops throughout the world's tropical and subtropical regions. On Australia's East Coast, two native species—Tetragonula carbonaria and Tetragonula hockingsi—are the most widely propagated in hives, but knowledge of their biology and ecology in natural nests remains poorly documented. Here we monitor a wild population of Tetragonula in remnant forest in south-east Queensland over a 5-year period to assess three aspects of their life history: (i) rates of colony mortality, (ii) rates of queen turnover and (iii) incidences of nest usurpation. The latter occurs when one colony usurps the nest cavity of another, installing its own queen and enslaving the existing workers and brood. The range of T. hockingsi has increased in recent decades due to hive trade and southward range expansion. Our study area was located in the southern region of overlap with T. carbonaria. A total of 58 wild colonies were identified within the study site (1.5 nests per hectare), three-quarters of which were T. carbonaria. Colony mortality averaged 8.3% per year, such that 40% of colonies had died by the end of the 5-year study interval. Sequencing of mitochondrial-COI and microsatellite genotyping of workers at four time points was used to infer that queen turnover (i.e., queens replaced by daughter queens) typically occurs every 20–30 months. Eight cases were detected consistent with interspecific nest usurpation, in all of which T. hockingsi replaced T. carbonaria. However, T. hockingsi colonies also had lower annual survivorship than those of T. carbonaria, resulting in a stable proportion of each species in the study area over time. Overall, results show that although nest occupancy by Tetragonula colonies is typically several years, colony death and nest usurpation are common in wild populations, and community composition is shaped by interspecific differences in both usurpation success and annual mortality.