Adipokinetic hormone (AKH), energy budget and their effect on feeding and gustatory processes of foraging honey bees

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.

The short neuropeptide F regulates appetitive but not aversive responsiveness in a social insect

“…This method is commonly used in many insect species to determine the effect of neurotransmitters, neuropeptides, and bioactive substances such as pesticides and other molecules of interest (e.g. Barron et al, 2007;Copijn et al, 1977;de Brito Sanchez et al, 2021;Hewlett et al, 2018;Killiny et al, 2014;Motta et al, 2020;Nouvian et al, 2018;Pankiw and Page, 2003;Park and Smith, 2021;Sierras and Schal, 2017). It has the advantage of preserving insects intact for behavioral analyzes, which is not the case when injections (e.g.…”

Systemic glucose levels are modulated by specific wavelengths in the solar light spectrum that shift mitochondrial metabolism

“…Upon feeding, glucose is transported from the crop to the haemolymph and if glucose levels exceed demand, is converted into trehalose by the fat body for storage. Trehalose is broken down into glucose, depleting reserves when demand increases during starvation [ 19 ]. A dynamic response of glucose also occurs during protracted periods of feeding or fasting [ 20 ].…”

“…Like mammals, insects possess peptide hormones that regulate these circulating carbohydrates, and the storage of lipid and glycogen in fat body and muscle. One example of which is a functional homolog of glucagon; adipokinetic hormone, stimulates trehalose release from glycogen, and diacylglycerol from triacylglycerol within the fat body [ 19 ]. Light modulation of glucose levels most likely represents a change in cell uptake and oxidation rate of it by mitochondria here, given the known mechanism; and supported by previous reports of increased respiration rate in healthy bumblebees following 670 nm light exposure [ 12 ].…”

Food wanting is mediated by transient activation of dopaminergic signaling in the honey bee brain

“…We reasoned that manipulating dopamine levels would change the hedonic value of sucrose solution and thus individual appetitive responsiveness. To test this hypothesis, foragers captured upon landing at a feeder were individually enclosed within syringes, which allowed them to be fed with 30 μl of 1.0 M sucrose solution via a tip inserted in the syringe hub ( 21 ). In this way, we reduced individual appetitive responsiveness to be able to observe behavioral changes due to artificial dopamine increase.…”