Octopamine mobilizes lipids from honey bee (Apis mellifera) hypopharyngeal glands

Authors: Corby-Harris, Vanessa; DEETER, MEGAN - University Of Arizona; Snyder, Lucy; Meador, Charlotte; GANDER, ASHLEY - University Of Arizona; Hoffman, Amelia

Submitted to: Journal of Experimental Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2020
Publication Date: 4/16/2020
Citation: Corby-Harris, V.L., Deeter, M.E., Snyder, L.A., Meador, C.A., Gander, A.C., Hoffman, A.D. 2020. Octopamine mobilizes lipids from honey bee (Apis mellifera) hypopharyngeal glands. Journal of Experimental Biology. 223(8). https://doi.org/10.1242/jeb.216135.
DOI: https://doi.org/10.1242/jeb.216135

Interpretive Summary: The hormone octopamine is a crucial player in the invertebrate stress response. When stressed, octopamine levels rise and enable physiological and behavioral responses that help the organism to either escape from or tolerate the stressor. One important physiological response induced by octopamine is the release of energy-rich lipids from storage tissues, which fuels the stress response. Honey bees experience and respond to stress. For example, stressed bees have depleted abdominal lipids and smaller hypopharyngeal glands (HGs), organs that produce the jelly that nourishes larvae and the queen. Unhealthy nurses can compromise colony health, so finding ways to prevent this stressful response could be used to improve colony health. Octopamine might offer such an option, but in order to find whether this is true, we need a better understanding of how it works in bees. In other words, does octopamine cause physiological changes that are associated with stress and that may compromise colony health? To this end, we tested whether octopamine induced the degradation of abdominal lipid stores and the HG glands. We found that the HGs, but not the abdominal lipids, degraded in response to hormonal treatment. This suggests that stress causes small nurse HGs via the action of octopamine. The relevance of this finding is that it offers a potential way of maintaining nurse HG size, even if environmental stressors cannot realistically be eliminated.

Technical Abstract: Recent widespread honey bee (Apis mellifera) colony loss is attributed to a variety of stressors including parasites, pathogens, pesticides, and poor nutrition. In principle, stress-induced colony loss can be reversed by either removing the stressor or increasing the honey bee’s tolerance to the stressor. This latter option requires a better understanding than we currently have of how honey bees respond to stress. Here, we investigated how octopamine, a stress-induced hormone that mediates physiological and behavioral processes in invertebrates, influences the health of young nurse-aged bees. Specifically, we asked whether octopamine induces abdominal lipid and hypopharyngeal gland (HG) degradation, two physiological traits of stressed nurse bees. Nurse-aged workers were treated topically with octopamine and their abdominal lipid content, HG size, and HG autophagic gene expression were measured. Hemolymph lipid titer was measured to determine whether tissue degradation was associated with the release of nutrients from these tissues into the hemolymph. The HGs of octopamine-treated bees were smaller than control bees and had higher levels of HG autophagy gene expression. Octopamine-treated bees also had higher levels of hemolymph lipid compared to control bees. Abdominal lipids did not change in response to octopamine. Our findings support the hypothesis that the HGs are a rich source of stored energy that can be mobilized during periods of stress. These results inform our understanding of the honey bee stress response and suggest potential methods that can be developed for preserving colony brood rearing in stressful situations.