The brain plasticity of the adult worker of the stingless bee Melipona quadrifasciata anthidioides depends on interactions with conspecifics

Stingless bees are important pollinators of cultivated and wild plants in tropical regions. These eusocial insects are extremely dependent on the interactions with conspecifics within the colony. It is known that these interactions can influence individual’s development, feeding, learning tasks and memory. In the present work the brain plasticity of the adult workers of the stingless bee Melipona quadrifasciata anthidioides (Apidae, Meliponinae) was studied in individuals allowed to age inside and outside the nest (i.e. in natural and in laboratory conditions, respectively). In the laboratory adults were kept individually in incubators (28°C, 24h scotophase) and were fed on honey syrup and pollen. The volumes of the antennal lobes (ALs) and mushroom bodies (MBs) of these two groups were compared.  Brains were dissected from workers with different ages (1-, 4-, 8- and 28-day-old), fixed in formaldehyde 4% in PBS and processed for sectioning. Serial sections were stained with hematoxylin and eosin and the ALs and MBs areas were measured and their volumes were determined by Cavalieri method. The volumes of ALs and MBs of bees aged in the nest increased with ageing (linear regression p<0.01 and p<0.0001 respectively). The bees aged in the laboratory had significantly smaller MBs in comparison to individuals from the field (t-test p <0.05) and died before the 28^th day, while ALs volume did not differ. Our results showed that the social interactions can interfere with the neuronal plasticity of adult worker stingless bees and we are currently investigating how it can interfere with their walking activity.