Abstract
The adipokinetic hormone (AKH) of insects is considered an equivalent of the mammalian hormone glucagon as it induces fast mobilization of carbohydrates and lipids from the fat body upon starvation. Yet, in foraging honey bees, which lack fat body storage for carbohydrates, it was suggested that AKH may have lost its original function. Here we manipulated the energy budget of bee foragers to determine the effect of AKH on appetitive responses. As AKH participates in a cascade leading to acceptance of unpalatable substances in starved Drosophila, we also assessed its effect on foragers presented with sucrose solution spiked with salicin. Starved and partially-fed bees were topically exposed with different doses of AKH to determine if this hormone modifies food ingestion and sucrose responsiveness. We found a significant effect of the energy budget (i.e. starved vs. partially-fed) on the decision to ingest or respond to both pure sucrose solution and sucrose solution spiked with salicin, but no effect of AKH per se. These results are consistent with a loss of function of AKH in honey bee foragers, in accordance with a social life that implies storing energy resources in the hive, in amounts that exceed individual needs.
Highlights
The adipokinetic hormone (AKH) of insects is considered an equivalent of the mammalian hormone glucagon as it induces fast mobilization of carbohydrates and lipids from the fat body upon starvation
We first analyzed if AKH affected the decision of starved bees to ingest food
We studied if AKH treatment enhanced the propensity of partially fed bees to consume the unpalatable sucrose solution spiked with salicin (Fig. 4b)
Summary
The adipokinetic hormone (AKH) of insects is considered an equivalent of the mammalian hormone glucagon as it induces fast mobilization of carbohydrates and lipids from the fat body upon starvation. Insects possess peptide hormones that are essential for regulating both carbohydrates circulating in the hemolymph and stored lipids and glycogen in the fat b ody[3], an organ that has been compared to the adipose tissue and liver due to its role in energy storage, utilization, and d etoxification[4] One of these hormones, the adipokinetic hormone (AKH)[5], is secreted by the corpora cardiaca (CC) and elicits both carbohydrate and lipid mobilization from the fat body (trehalose from glycogen and diacylglycerol from triacylglycerol, respectively), acting as a functional homolog of glucagon[6,7]. When the stores of glycogen are exhausted, carbohydrates might be synthesized from other sources[15]
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