Seasonality, alarm pheromone and serotonin: insights on the neurobiology of honeybee defence from winter bees

Honey Robbing: Causes, Impacts and Preventive Measures

Honey robbing, which typically occurs during times of food scarcity, is a perilous foraging strategy for bee colonies and presents a formidable challenge in the realm of beekeeping. This article provides a comprehensive and multifaceted exploration of honey robbing, including the morphology, behavioral traits, timing, and scope of this phenomenon. This exploration elucidates the specific manifestations of honey robbing, offering readers a deeper understanding of its various facets. Next, this article investigates the root causes of honey robbing by examining both abiotic and biotic factors. The resulting harms are outlined, and corresponding preventive and control measures are suggested. Finally, the article succinctly summarizes the current obstacles in research related to honey robbing and outlines promising avenues for future exploration. The objective of this study was to elucidate the occurrence mechanism of honey robbing, ultimately aiming to contribute to the sustainable growth of the beekeeping industry.

Analysis of fast calcium dynamics of honey bee olfactory coding

Odour processing exhibits multiple parallels between vertebrate and invertebrate olfactory systems. Insects, in particular, have emerged as relevant models for olfactory studies because of the tractability of their olfactory circuits. Here, we used fast calcium imaging to track the activity of projection neurons in the honey bee antennal lobe (AL) during olfactory stimulation at high temporal resolution. We observed a heterogeneity of response profiles and an abundance of inhibitory activities, resulting in various response latencies and stimulus-specific post-odour neural signatures. Recorded calcium signals were fed to a mushroom body (MB) model constructed implementing the fundamental features of connectivity between olfactory projection neurons, Kenyon cells (KC), and MB output neurons (MBON). The model accounts for the increase of odorant discrimination in the MB compared to the AL and reveals the recruitment of two distinct KC populations that represent odorants and their aftersmell as two separate but temporally coherent neural objects. Finally, we showed that the learning-induced modulation of KC-to-MBON synapses can explain both the variations in associative learning scores across different conditioning protocols used in bees and the bees' response latency. Thus, it provides a simple explanation of how the time contingency between the stimulus and the reward can be encoded without the need for time tracking. This study broadens our understanding of olfactory coding and learning in honey bees. It demonstrates that a model based on simple MB connectivity rules and fed with real physiological data can explain fundamental aspects of odour processing and associative learning.

Defense in Social Insects: Diversity, Division of Labor, and Evolution

All social insects defend their colony from predators, parasites, and pathogens. In Oster and Wilson's classic work, they posed one of the key paradoxes about defense in social insects: Given the universal necessity of defense, why then is there so much diversity in mechanisms? Ecological factors undoubtedly are important: Predation and usurpation have imposed strong selection on eusocial insects, and active defense by colonies is a ubiquitous feature of all social insects. The description of diverse insect groups with castes of sterile workers whose main duty is defense has broadened the purview of social evolution in insects, in particular with respect to caste and behavior. Defense is one of the central axes along which we can begin to organize and understand sociality in insects. With the establishment of social insect models such as the honey bee, new discoveries are emerging regarding the endocrine, neural, and gene regulatory mechanisms underlying defense in social insects. The mechanisms underlying morphological and behavioral defense traits may be shared across diverse groups, providing opportunities for identifying both conserved and novel mechanisms at work. Emerging themes highlight the context dependency of and interaction between factors that regulate defense in social insects.

Detection of Serotonin, Melatonin, and Their Metabolites in Honey

Melatonin and serotonin, products of tryptophan metabolism, are endogenous neurotransmitters and hormones. We have identified and quantified these metabolites in natural honey from Australia, USA, and Poland using a Xevo G2 XS qTof LC-MS. To help ensure correct product identification, some samples were prepurified by RP-HPLC based on the retention times of standards, prior to LC-MS. The concentrations of the metabolites of interest depended on the source of the honey. For Australian honey, levels for melatonin and 2-hydroxymelatonin were 0.91 and 0.68 ng/g, respectively. Melatonin was detected in one brand of US commercial honey at 0.48 ng/g, while a second brand contained serotonin at 88.2 ng/g. In Polish natural honey, 20.6 ng/g of serotonin and 40.8 ng/g of N-acetylserotonin (NAS) were detected, while in Polish commercial honey 25.9 ng/g of serotonin and 7.30 ng/g of NAS were present. We suggest that addictive and health-related properties of honey may be in part dependent on the presence of serotonin, melatonin, and their metabolites, and that these compounds may play a role in the colony activities of bees.

Seasonality, alarm pheromone and serotonin: insights on the neurobiology of honeybee defence from winter bees

Honeybees maintain their colony throughout the cold winters, a strategy that enables them to make the most of early spring flowers. During this period, their activity is mostly limited to thermoregulation, while foraging and brood rearing are stopped. Less is known about seasonal changes to the essential task of defending the colony against intruders, which is regulated by the sting alarm pheromone. We studied the stinging responsiveness of winter bees exposed to this scent or a control (solvent). Surprisingly, winter bees, while maintaining their responsiveness in control conditions, did not increase stinging frequency in response to the alarm pheromone. This was not owing to the bees not perceiving the pheromone, as shown by calcium imaging of the antennal lobes. As the alarm pheromone is thought to act through an increase in brain serotonin levels, ultimately causing heightened defensiveness, we checked if serotonin treatments would affect the stinging behaviour of winter bees. Indeed, treated winter bees became more inclined to sting. Thus, we postulate that loss of responsiveness to the sting alarm pheromone is based on a partial or total disruption of the mechanism converting alarm pheromone perception into high serotonin levels in winter bees.