Why do stingless bees (Melipona subnitida) leave their nest with resin loads?
Stingless bees (Apidae, Meliponini) collect plant resins and deliver them to their nest for use as construction material. In some species, however, workers can be observed leaving their colonies with resin loads on their corbiculae. The present study investigated the role of these "resin bees" in the Brazilian stingless bee Melipona subnitida. In 7 nests, we observed a total of 424 workers departing the nest under undisturbed colony conditions. One tenth (11.3%) of these outgoing bees carried resin on their corbiculae. The average weight of the loads was 5.2 mg, approximately, 10% of the bees' body weight. The round-trip duration of resin bees (1.3 min) was significantly shorter than that of nectar foragers (12.3 min). When the colonies were experimentally disturbed, the majority of the agitated bees that left the colony in response carried resin loads (90.5%). Our results suggest that resin bees in M. subnitida are nest defenders. Under undisturbed colony conditions, these bees may perform surveillance flights close to the nest, watching out for potential intruders and even mummify them with resin. Additionally, the deterrent effect of plant resins on many bee predators may reduce the workers' risk during these flights.
KeywordsGuard bee Nest defence Propolis Plant resin
We are grateful to Gustavo Medeiros da Silva for the permission to use his colonies of M. subnitida for this study, and Dr. Shinya Hayashi for statistical support. We also thank Nico Blüthgen and two anonymous referees for their valuable suggestions and comments on our manuscript. This study was partially supported by a long-term training program of Tamagawa University and a JSPS (Japan Society for the Promotion of Science) Kakenhi Grant No. 17K08154 to KH.
KH contributed to the study conception and design. CM-S and MH performed material preparation. KH performed data collection and analysis. KH and MH wrote the manuscript. All authors read and approved the final manuscript.
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