Experience-expectant plasticity in the mushroom bodies of the honeybee

Worker honeybees (Apis mellifera) were reared in social isolation in comple te darkness to assess the effects of experience on growth of the neuropil o f the mushroom bodies (MBs) during adult Life. Comparison of the volume of the MBs of 1-day-old and 7-day-old bees showed that a significant increase Ln volume in the MB neuropil occurred during the first week of Life in bees reared under these highly deprived conditions. All regions of the MB neuro pil experienced a significant increase in volume with the exception of the basal ring. Measurement of titers of juvenile hormone (JH) in a subset of b ees indicated that, as in previous studies, these rearing conditions induce d in some bees the endocrine state of high JH associated with foraging, but there was no correlation between JH titer and volume of MB neuropil. Treat ment of another subset of dark-reared bees with the JH analog, methoprene, also had no effect of the growth of the MB neuropil. These results demonstr ate that there is a phase of MB neuropil growth early in the adult Life of bees that occurs independent of light or any form of social interaction. To gether with previous findings showing that an increase in MB neuropil volum e begins around the time that orientation flights occur and then continues throughout the phase of Life devoted to foraging, these results suggest tha t growth of the MB neuropil in adult bees may have both experience-expectan t and experience-dependent components.