The Appropriate Supplementary Level of Tryptophan in the Diet ofApis mellifera(Hymenoptera: Apidae) Worker Bees

This study was designed to determine the appropriate levels of tryptophan (trp) in the diet of Apis mellifera worker bees. Newly emerged worker bees were enclosed in wooden cages in an incubator at 32°C with 55–60% humidity and fed a diet including 9, 10, 11, 12, 13, and 14 mg/g trp for 12 days. When the trp level was 11 mg/g, worker bees demonstrated better performance in terms of food intake, body weight, and total protein accumulation. However, 12 mg/g dietary trp promoted trp deposition in the worker bees, stimulated hypopharyngeal gland development, enhanced the survival rate and expedited the formation of 5-HT (5-hydroxytryptamine). The worker bees fed with 13 and 14 mg/g trp had higher malondialdehyde (MDA) levels, which suggested that a higher level of trp may be disadvantageous in maintaining worker-bee antioxidant ability, because MDA was the end product of lipid peroxidation. We also found that dietary trp regulated the mRNA expression of 5-HTRs and tryptophan hydroxylase (TPH) in a dose-dependent manner, which was related to phototaxis, aggression, and other factors. In conclusion, dietary trp exerts regulatory roles in the growth, development and some physiological and biochemical properties of worker bees. Therefore, 11–12 mg/g tryptophan is optimal for A. mellifera adult worker bees.