Division of labor in the honey bee (Apis mellifera): The role of tyramine β-hydroxylase

The biogenic amine octopamine (OA) is involved in the regulation of honey bee behavioral development; brain levels are higher in foragers than bees working in the hive, especially in the antennal lobes, and treatment causes precocious foraging. We measured brain mRNA and protein activity of tyramine β-hydroxylase (Tβh), an enzyme vital for OA synthesis, in order to begin testing the hypothesis that this enzyme is responsible for the rising levels of OA during honey bee behavioral development. Brain OA levels were greater in forager bees than in bees engaged in brood care, as in previous studies, but Tβh activity was not correlated with bee behavior. Tβh mRNA levels, however, did closely track OA levels during behavioral development, and Tβh mRNA was localized to previously identified octopaminergic neurons in the bee brain. Our results show that the transcription of this neurotransmitter synthetic enzyme is associated with regulation of social behavior in honey bees, but other factors may be involved.