Scanning electron microscopy (SEM) reveals high diversity of setae on the hind tibiae and basitarsi of Peruvian Stingless Bees (Apidae: Meliponini)

Stingless bees belong to the group of corbiculate bees, all characterized by the presence of a corbicula, a specialized structure of the hind tibia used for pollen collection. This group exhibits significant variation in foraging behavior, from flower-visiting foragers to kleptoparasites and obligate necrophagous. So far, scanning electron microscopy (SEM) studies have been mainly focused on the hind leg setae of Apis spp. and Bombus spp. Here, we performed a comparative morphological analysis of the setae and the pollen handling structures in the hind tibiae and basitarsi of seven stingless bee species: the floral pollen collector bees Melipona cf. eburnea, Partamona testacea, Scaura cf. latitarsis, Trigonisca cf. atomaria, Trigona dallatorreana, the robber bee Lestrimelitta sp. and the obligate necrophagous Trigona cf. hypogea, collected in Peruvian forests in 2020. The setae were classified into simple and branched types, subdivided into five and seven subtypes, respectively. In addition, we described three types of penicillum, five types of rastellum, three types of pollen brush, two types of setae covering the auricular area, and show the setae forming the sericeous area of Trigona spp. Finally, seven types of keirotrichia are described. We highlight that certain types of setae show a high degree of conservation across species, while others are unique and potentially indicative of adaptive specialization. Among species that have abandoned pollen foraging on flowers, we observed a simplification in the number of setal types and the absence of pollen handling structures in Lestrimelitta sp., whereas T. cf. hypogea exhibits the highest diversity of setae and retains most of these structures. Finally, based on these two species, we reflect on the link between reduced corbicula and functional corbicula. The study highlights the importance of further exploring the mechanical and sensory roles of setae and expanding this research in Meliponini. Such investigations can improve our understanding of their adaptive functions and provide valuable insights into the functional ecology, taxonomy and phylogenetic studies of these tropical pollinators.