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

The brain atlas of a subsocial bee reflects that of eusocial Hymenoptera

The evolutionary transition from solitary life to group-living in a society with cooperative brood care, reproductive division of labor and morphological castes is associated with increased cognitive demands for task-specialization. Associated with these demands, the brains of eusocial Hymenoptera divide transcriptomic signatures associated with foraging and reproduction to different populations of cells and also show diverse astrocyte and Kenyon cell types compared with solitary non-hymenopteran insects. The neural architecture of subsocial bees, which represent evolutionary antecedent states to eusocial Hymenoptera, could then show how widely this eusocial brain is conserved across aculeate Hymenoptera. Using single-nucleus transcriptomics, we have created an atlas of neuron and glial cell types from the brain of a subsocial insect, the small carpenter bee (Ceratina calcarata). The proportion of C. calcarata neurons related to the metabolism of classes of neurotransmitters is similar to that of other insects, whereas astrocyte and Kenyon cell types show highly similar gene expression patterns to those of eusocial Hymenoptera. In the winter, the transcriptomic signature across the brain reflected diapause. When the bee was active in the summer, however, genes upregulated in neurons reflected foraging, while the gene expression signature of glia associated with reproductive functions. Like eusocial Hymenoptera, we conclude that neural components for foraging and reproduction in C. calcarata are compartmentalized to different parts of its brain. Cellular examination of the brains of other solitary and subsocial insects can show the extent of neurobiological conservation across levels of social complexity.

The complex neurochemistry of the cockroach antennal heart

The innervation of the antennal heart of the cockroach Periplaneta americana was studied with immunocytochemical techniques on both the light and electron microscopic levels. The antennal heart is innervated by two efferent systems, both using one biogenic amine in combination with neuropeptides. In one, we found co-localization of serotonin with proctolin and allatostatin. These fibers most likely originate from paired neurons located in the suboesophageal ganglion. In the second system, we found octopamine co-localized with the short neuropeptide F. The source of this second system is dorsal unpaired median (DUM) neurons, also located in the suboesophageal ganglion. The possible effects of these neuromediators on different targets are discussed.

When the society dictates food search - Neural signalling underlying appetitive motivation in honey bees

In honey bees, appetitive motivation is primarily driven by the needs of the colony rather than individual needs. The regulation of appetitive behavior is achieved through the coordinated action of neuropeptides, hormones and biogenic amines, which integrate multiple signals to ensure appropriate appetitive responses. Dopamine signalling underpins a food-related wanting system that is sensitive to aversive experiences. The short neuropeptide F (sNPF) enhances appetitive responsiveness, food intake and behavioral and neural responsiveness to food-related odorants. Additionally, it facilitates appetitive learning and memory. On the contrary, tachykinin-related peptides (TRPs) inhibit appetitive responses. Physiological changes during the transition to the foraging state lead to distinct patterns of insulin and adipokinetic hormone (AKH) signaling, different from those seen in solitary insects, indicating that social life had significant consequences on the systems controlling appetitive motivation. Overall, studying the neural bases of appetitive behavior in bees reveals unique aspects that arise from their social lifestyle.

Complicated gene network for regulating feeding behavior: novel efficient target for pest management

Feeding behavior is a fundamental activity for insects, which is essential for their growth, development and reproduction. The regulation of their feeding behavior is a complicated process influenced by a variety of factors, including external stimuli and internal physiological signals. The current review introduces the signaling pathways in brain, gut and fat body involved in insect feeding behavior, and provides a series of target genes for developing RNA pesticides. Additionally, this review summaries the current challenges for the identification and application of functional genes involved in feeding behavior, and finally proposes the future research direction. © 2024 Society of Chemical Industry.

Pesticides and pollinator brain: How do neonicotinoids affect the central nervous system of bees?

Neonicotinoids represent over a quarter of the global pesticide market. Research on their environmental impact has revealed their adverse effect on the cognitive functions of pollinators, in particular of bees. Cognitive impairments, mostly revealed by behavioural studies, are the phenotypic expression of an alteration in the underlying neural circuits, a matter deserving greater attention. Here, we reviewed studies on the impact of field-relevant doses of neonicotinoids on the neurophysiology and neurodevelopment of bees. In particular, we focus on their olfactory system as much knowledge has been gained on the different brain areas that participate in odour processing. Recent studies have revealed the detrimental effects of neonicotinoids at multiple levels of the olfactory system, including modulation of odorant-induced activity in olfactory sensory neurons, diminished neural responses in the antennal lobe (the first olfactory processing centre) and abnormal development of the neural connectivity within the mushroom bodies (central neuropils involved in multisensory integration, learning and memory storage, among others). Given the importance of olfactory perception for multiple aspects of bee biology, the reported disruption of the olfactory circuit, which can occur even upon exposure to sublethal doses of neonicotinoids, has severe consequences at both individual and colony levels. Moreover, the effects reported for a multimodal structure such as the mushroom bodies indicate that neonicotinoids' impact translates to other sensory domains. Assessing the impact of field-relevant doses of pesticides on bee neurophysiology is crucial for understanding how neonicotinoids influence their behaviour in ecological contexts and for defining effective and sustainable agricultural practices.

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.

CalciSeg: A versatile approach for unsupervised segmentation of calcium imaging data

Recent advances in calcium imaging, including the development of fast and sensitive genetically encoded indicators, high-resolution camera chips for wide-field imaging, and resonant scanning mirrors in laser scanning microscopy, have notably improved the temporal and spatial resolution of functional imaging analysis. Nonetheless, the variability of imaging approaches and brain structures challenges the development of versatile and reliable segmentation methods. Standard techniques, such as manual selection of regions of interest or machine learning solutions, often fall short due to either user bias, non-transferability among systems, or computational demand. To overcome these issues, we developed CalciSeg, a data-driven and reproducible approach for unsupervised functional calcium imaging data segmentation. CalciSeg addresses the challenges associated with brain structure variability and user bias by offering a computationally efficient solution for automatic image segmentation based on two parameters: regions' size limits and number of refinement iterations. We evaluated CalciSeg efficacy on datasets of varied complexity, different insect species (locusts, bees, and cockroaches), and imaging systems (wide-field, confocal, and multiphoton), showing the robustness and generality of our approach. Finally, the user-friendly nature and open-source availability of CalciSeg facilitate the integration of this algorithm into existing analysis pipelines.

Short neuropeptide F in integrated insect physiology

The short neuropeptide F (sNPF) family of peptides is a multifunctional group of neurohormones involved in the regulation of various physiological processes in insects. They have been found in a broad spectrum of species, but the number of isoforms in the precursor molecule varies from one to four. The receptor for sNPF (sNPFR), which belongs to the G protein-coupled receptor family, has been characterized in various insect orders and was shown to be an ortholog of the mammalian prolactin-releasing peptide receptor (PrPR). The sNPF signaling pathway interacts with other neurohormones such as insulin-like peptides, SIFamide, and pigment-dispersing factors (PDFs) to regulate various processes. The main physiological function of sNPF seems to be involved in the regulation of feeding, but the observed effects are species-specific. sNPF is also connected with the regulation of foraging behavior and the olfactory system. The influence of sNPF on feeding and thus energy metabolism may also indirectly affect other vital processes, such as reproduction and development. In addition, these neurohormones are involved in the regulation of locomotor activity and circadian rhythm in insects. This review summarizes the current state of knowledge about the sNPF system in insects.

Effect of short neuropeptide F signaling on larval feeding in Mythimna separata

Mythimna separata is a notorious phytophagous pest which poses serious threats to cereal crops owing to the gluttony of the larvae. Because short neuropeptide F (sNPF) and its receptor sNPFR are involved in a diversity of physiological functions, especially in functions related to feeding in insects, it is a molecular target for pest control. Herein, an sNPF and 2 sNPFRs were identified and cloned from M. separata. Bioinformatics analysis revealed that the sNPF and its receptors had a highly conserved RLRFamide C-terminus and 7 transmembrane domains, respectively. The sNPF and its receptor genes were distributed across larval periods and tissues, but 2 receptors had distinct expression patterns. The starvation-induced assay elucidated that sNPF and sNPFR expression levels were downregulated under food deprivation and recovered with subsequent re-feeding. RNA interference knockdown of sNPF, sNPFR1, and sNPFR2 by injection of double-stranded RNA into larvae not only suppressed food consumption and increased body size and weight, but also led to decrease of glycogen and total lipid contents, and increase of trehalose compared with double-stranded green fluorescent protein injection. Furthermore, molecular docking was performed on the interaction mode between sNPFR protein and its ligand sNPF based on the 3-dimensional models constructed by AlphaFold; the results indicated that both receptors were presumably activated by the mature peptide sNPF-2. These results revealed that sNPF signaling played a considerably vital role in the feeding regulation of M. separata and represents a potential control target for this pest.

Neuroregulation of foraging behavior mediated by the olfactory co-receptor Orco in termites

Olfaction is critical for survival because it allows animals to look for food and detect pheromonal cues. Neuropeptides modulate olfaction and behaviors in insects. While how the neuroregulation of olfactory recognition affects foraging behavior in termites is still unclear. Here, we analyzed the change after silencing the olfactory co-receptor gene (Orco) and the neuropeptide Y gene (NPY), and then investigated the impact of olfactory recognition on foraging behavior in Odontotermes formosanus under different predation pressures. The knockdown of Orco resulted in the reduced Orco protein expression in antennae and the decreased EAG response to trail pheromones. In addition, NPY silencing led to the damaged ability of olfactory response through downregulating Orco expression. Both dsOrco- and dsNPY-injected worker termites showed significantly reduced walking activity and foraging success. Additionally, we found that 0.1 pg/cm trail pheromone and nestmate soldiers could provide social buffering to relieve the adverse effect of predator ants on foraging behavior in worker termites with the normal ability of olfactory recognition. Our orthogonal experiments further verified that Orco/NPY genes are essential in manipulating termite olfactory recognition during foraging under different predation pressures, suggesting that the neuroregulation of olfactory recognition plays a crucial role in regulating termite foraging behavior.

Neuropeptide regulations on behavioral plasticity in social insects

Social insects demonstrate remarkable behavioral flexibility in response to complex external and social environments. One of the most striking examples of this adaptability is the context-dependent division of labor among workers of bees and ants. Neuropeptides, the brain's most diverse group of messenger molecules, play an essential role in modulating this phenotypic plasticity related to labor division in social insects. Integrated omics research and mass spectrometry imaging technology have greatly accelerated the identification and spatiotemporal analysis of neuropeptides. Moreover, key roles of several neuropeptides in age- and caste-dependent behavioral plasticity have been uncovered. This review summarizes recent advances in the characterization, expression, distribution, and functions of neuropeptides in controlling behavioral plasticity in social insects, particularly bees and ants. The article concludes with a discussion of future directions and challenges in understanding the regulation of social behavior by neuropeptides.

Efficient visual learning by bumble bees in virtual-reality conditions: Size does not matter

Recent developments allowed establishing virtual-reality (VR) setups to study multiple aspects of visual learning in honey bees under controlled experimental conditions. Here, we adopted a VR environment to investigate the visual learning in the buff-tailed bumble bee Bombus terrestris. Based on responses to appetitive and aversive reinforcements used for conditioning, we show that bumble bees had the proper appetitive motivation to engage in the VR experiments and that they learned efficiently elemental color discriminations. In doing so, they reduced the latency to make a choice, increased the proportion of direct paths toward the virtual stimuli and walked faster toward them. Performance in a short-term retention test showed that bumble bees chose and fixated longer on the correct stimulus in the absence of reinforcement. Body size and weight, although variable across individuals, did not affect cognitive performances and had a mild impact on motor performances. Overall, we show that bumble bees are suitable experimental subjects for experiments on visual learning under VR conditions, which opens important perspectives for invasive studies on the neural and molecular bases of such learning given the robustness of these insects and the accessibility of their brain.

Granger Causality Analysis of Transient Calcium Dynamics in the Honey Bee Antennal Lobe Network

Odorant processing presents multiple parallels across animal species, and insects became relevant models for the study of olfactory coding because of the tractability of the underlying neural circuits. Within the insect brain, odorants are received by olfactory sensory neurons and processed by the antennal lobe network. Such a network comprises multiple nodes, named glomeruli, that receive sensory information and are interconnected by local interneurons participating in shaping the neural representation of an odorant. The study of functional connectivity between the nodes of a sensory network in vivo is a challenging task that requires simultaneous recording from multiple nodes at high temporal resolutions. Here, we followed the calcium dynamics of antennal lobe glomeruli and applied Granger causality analysis to assess the functional connectivity among network nodes in the presence and absence of an odorous stimulus. This approach revealed the existence of causal connectivity links between antennal lobe glomeruli in the absence of olfactory stimulation, while at odor arrival, the connectivity network's density increased and became stimulus-specific. Thus, such an analytical approach may provide a new tool for the investigation of neural network plasticity in vivo.

Changes in resource perception throughout the foraging visit contribute to task specialization in the honey bee Apis mellifera

Division of labor is central to the ecological success of social insects. Among foragers of the honey bee, specialization for collecting nectar or pollen correlates with their sensitivity to sucrose. So far, differences in gustatory perception have been mostly studied in bees returning to the hive, but not during foraging. Here, we showed that the phase of the foraging visit (i.e. beginning or end) interacts with foraging specialization (i.e. predisposition to collect pollen or nectar) to modulate sucrose and pollen sensitivity in foragers. In concordance with previous studies, pollen foragers presented higher sucrose responsiveness than nectar foragers at the end of the foraging visit. On the contrary, pollen foragers were less responsive than nectar foragers at the beginning of the visit. Consistently, free-flying foragers accepted less concentrated sucrose solution during pollen gathering than immediately after entering the hive. Pollen perception also changes throughout foraging, as pollen foragers captured at the beginning of the visit learned and retained memories better when they were conditioned with pollen + sucrose as reward than when we used sucrose alone. Altogether, our results support the idea that changes in foragers' perception throughout the foraging visit contributes to task specialization.

Descending control of nociception in insects?

Modulation of nociception allows animals to optimize chances of survival by adapting their behaviour in different contexts. In mammals, this is executed by neurons from the brain and is referred to as the descending control of nociception. Whether insects have such control, or the neural circuits allowing it, has rarely been explored. Based on behavioural, neuroscientific and molecular evidence, we argue that insects probably have descending controls for nociception. Behavioural work shows that insects can modulate nocifensive behaviour. Such modulation is at least in part controlled by the central nervous system since the information mediating such prioritization is processed by the brain. Central nervous system control of nociception is further supported by neuroanatomical and neurobiological evidence showing that the insect brain can facilitate or suppress nocifensive behaviour, and by molecular studies revealing pathways involved in the inhibition of nocifensive behaviour both peripherally and centrally. Insects lack the endogenous opioid peptides and their receptors that contribute to mammalian descending nociception controls, so we discuss likely alternative molecular mechanisms for the insect descending nociception controls. We discuss what the existence of descending control of nociception in insects may reveal about pain perception in insects and finally consider the ethical implications of these novel findings.

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

The biological bases of wanting have been characterized in mammals, but whether an equivalent wanting system exists in insects remains unknown. In this study, we focused on honey bees, which perform intensive foraging activities to satisfy colony needs, and sought to determine whether foragers leave the hive driven by specific expectations about reward and whether they recollect these expectations during their waggle dances. We monitored foraging and dance behavior and simultaneously quantified and interfered with biogenic amine signaling in the bee brain. We show that a dopamine-dependent wanting system is activated transiently in the bee brain by increased appetite and individual recollection of profitable food sources, both en route to the goal and during waggle dances. Our results show that insects share with mammals common neural mechanisms for encoding wanting of stimuli with positive hedonic value.

The short neuropeptide F (sNPF) promotes the formation of appetitive visual memories in honey bees

Motivation can critically influence learning and memory. Multiple neural mechanisms regulate motivational states, among which signalling via specific neuropeptides, such as NPY in vertebrates and NPF and its short variant sNPF in invertebrates, plays an essential role. The honey bee (Apis mellifera) is a privileged model for the study of appetitive learning and memory. Bees learn and memorize sensory cues associated with nectar reward while foraging, and their learning is affected by their feeding state. However, the neural underpinnings of their motivational states remain poorly known. Here we focused on the short neuropeptide F (sNPF) and studied if it modulates the acquisition and formation of colour memories. Artificially increasing sNPF levels in partially fed foragers with a reduced motivation to learn colours resulted in significant colour learning and memory above the levels exhibited by starved foragers. Our results thus identify sNPF as a critical component of motivational processes involved in foraging and in the cognitive processes associated with this activity in honey bees.