PIGMENT-DISPERSING-FACTOR AND CORAZONIN IMMUNOREACTIVITY IN THE CENTRAL NERVOUS SYSTEM OF THE STINGLESS BEE (Melipona quadrifasciata)

*Correspondding aurhor e-mail: ycintia@usp.br Introduction: The stingless bees colony comprises a queen, workers of different ages that perform different tasks and males only present before the queen’s fecundation. Among the workers, only the oldest ones — foragers — keep a direct contact with the light/ dark environmental cycle. Biological rhythms are present and are controlled by the circadian system located in the central nervous system and in the retrocerebral complex. This system is composed by a web of multiple oscillators coupled to input pathways from the sensorial system and output pathways. The output pathways consist of nervous, neurohormonal and hormonal components. Several studies suggest the participation of the Pigment Dispersing Factor (PDF), a neuropeptide, in the output pathyways of the circadian system and in the synchronization of central oscillators. Another neuropeptide, Corazonin, seems to be envolved in dowstream output pathways. Methods: The objective of this study was to identify putative circadian pacemakers of the stingless bee, Melipona quadrifasciata . The central nervous system and the retrocerebral complex of foragers were analyzed throughout immunocitochemical assays. An antibody against Drosophila melanogaster PDF and another against Apis mellifera Corazonin have been used. Analysis and an accurate recognition of the brain’s areas of M. quadrifasciata were previously made by the central nervous system mapping. Results: PDF and Corazonin immunoreactivity (-ir) were present in the central nervous system of M. quadrifasciata . PDF-ir was localized in the cells and processes of the optic lobe, in all of its three neuropils: lamina , medulla and lobula . In the brain, the localization of PDF-ir cells suggests the presence of this neuropeptide in the pars lateralis (one of the largest clusters of brain’s neurosecretory cells). These results are distinct from previous descriptions of the honeybee’s system. Corazonin-ir was found in the brain of the stingless bee in two groups of cells localized in the protocerebrum (anterior portion of the brain), that apparently also belong to pars lateralis . Corazonin was found in the glands of the retrocerebral complex - corpora cardiaca and corpora allata - as well. Its presence in these glands has been recently reported in other insect species. Conclusion: The specific immunoreactivity of both PDF and Corazonin indicates the localization of circadian pacemakers and its efferences in the central nervous system of the stingless bee. These assays are the first studies that aim to identify the components and the organization of the circadian system of the stingless bee. Support: CNPq Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil