Brain melatonin content and polyethism in adult workers of Apis mellifera and Apis cerana (Hym., Apidae)

Abstract: Radioimmunoassay showed that melatonin, N ‐acetyl‐5‐methoxytryptamine, was synthesized in the brain of workers of Apis mellifera ligustica Spinola, and related to the polyethism of the workers. Statistically significant differences were found in melatonin levels between workers at different ages and between workers performing different tasks. The level in foragers was higher than that in young nurses. The highest melatonin level was found in 21‐day‐old adult workers (213.15 pg per worker head) and the lowest level in 1‐day‐old adult workers (6.08 pg per worker head); and the highest level in pollen‐collecting workers (404.13 pg per worker head) and the lowest in nurse workers (13.10 pg per worker head). Apis cerana cerana Fabricius showed a similar pattern, but the nectar foragers had the highest melatonin levels. The melatonin level also showed a daily rhythm. In 30‐day‐old adult workers there were two peaks, at 7:00 and 19:00 hours, and three troughs at 15:00, 21:00 and 1:00 hours respectively.