Ageing in a eusocial insect: molecular and physiological characteristics of life span plasticity in the honey bee

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.

The diverse roles of insulin signaling in insect behavior

In insects and other animals, nutrition-mediated behaviors are modulated by communication between the brain and peripheral systems, a process that relies heavily on the insulin/insulin-like growth factor signaling pathway (IIS). Previous studies have focused on the mechanistic and physiological functions of insulin-like peptides (ILPs) in critical developmental and adult milestones like pupation or vitellogenesis. Less work has detailed the mechanisms connecting ILPs to adult nutrient-mediated behaviors related to survival and reproductive success. Here we briefly review the range of behaviors linked to IIS in insects, from conserved regulation of feeding behavior to evolutionarily derived polyphenisms. Where possible, we incorporate information from Drosophila melanogaster and other model species to describe molecular and neural mechanisms that connect nutritional status to behavioral expression via IIS. We identify knowledge gaps which include the diverse functional roles of peripheral ILPs, how ILPs modulate neural function and behavior across the lifespan, and the lack of detailed mechanistic research in a broad range of taxa. Addressing these gaps would enable a better understanding of the evolution of this conserved and widely deployed tool kit pathway.

The Morphological Image of Fat Body and Tergal Gland Cells in Uninseminated Apis mellifera Queen Bees

The morphological changes in fat body cells, tergal gland cells, and the surface areas of the cell nuclei were determined in queen bees of the subspecies Apis mellifera carnica. This study focused on 1-, 8-, and 20-day-old uninseminated females kept in colonies, analyzing cells from three locations in the abdomen: the sternite, and tergites III and V. The oenocytes in the sternites were large, oval/circular with a centrally located nucleus, while in tergites III and V, they were small and triangular in the 1-day-old queens. During the first week of life, these cells in tergites III and V change their shape to oval and increase their sizes. The initially light yellow and then dark yellow granularities in the oenocytes of the fat body appear along with the advancing age of the queens. The trophocytes (sternites, tergites III and V) in the 1-day-old queens were completely filled with droplets of different sizes. In the 8- and 20-day-old queens, the number and size of the droplets decreased in the trophocytes of tergites III and V. The tergal gland cells had a centrally located cell nucleus in the 1-, 8- and 20-day-old queens. The dark granularities in these cells were visible only in the 20-day-old queens. Different morphological images of the fat body at the sternite, and tergites III and V, and the difference in the size of the oenocyte cell nuclei may indicate various functions of the fat body depending on its location. Characterization of the changes in the morphology of the fat body, taking into account its segmental character, and the tergal glands requires further research in older queens, e.g., one-year-old, brooding queens.

Age-related flexibility of energetic metabolism in the honey bee Apis mellifera

The mechanisms that underpin aging are still elusive. In this study, we suggest that the ability of mitochondria to oxidize different substrates, which is known as metabolic flexibility, is involved in this process. To verify our hypothesis, we used honey bees (Apis mellifera carnica) at different ages, to assess mitochondrial oxygen consumption and enzymatic activities of key enzymes of the energetic metabolism as well as ATP5A1 content (subunit of ATP synthase) and adenylic energy charge (AEC). We also measured mRNA abundance of genes involved in mitochondrial functions and the antioxidant system. Our results demonstrated that mitochondrial respiration increased with age and favored respiration through complexes I and II of the electron transport system (ETS) while glycerol-3-phosphate (G3P) oxidation was relatively decreased. In addition, glycolytic, tricarboxylic acid cycle and ETS enzymatic activities increased, which was associated with higher ATP5A1 content and AEC. Furthermore, we detected an early decrease in the mRNA abundance of subunits of NADH ubiquinone oxidoreductase subunit B2 (NDUFB2, complex I), mitochondrial cytochrome b (CYTB, complex III) of the ETS as well as superoxide dismutase 1 and a later decrease for vitellogenin, catalase and mitochondrial cytochrome c oxidase subunit 1 (COX1, complex IV). Thus, our study suggests that the energetic metabolism is optimized with aging in honey bees, mainly through quantitative and qualitative mitochondrial changes, rather than showing signs of senescence. Moreover, aging modulated metabolic flexibility, which might reflect an underpinning mechanism that explains lifespan disparities between the different castes of worker bees.

Study of Melipona quadrifasciata brain under operant learning using proteomic and phosphoproteomic analysis

Learning to anticipate events based on the predictive relationship between an action and an outcome (operant conditioning) is a form of associative learning shared by humans and most of other living beings, including invertebrates. Several behavioral studies on the mechanisms of operant conditioning have included Melipona quadrifasciata, a honey bee that is easily manipulated due to lack of sting. In this work, brain proteomes of Melipona bees trained using operant conditioning and untrained (control) bees were compared by two-dimensional gel electrophoresis analysis within pI range of 3-10 and 4-7; in order to find proteins specifically related to this type of associative learning.One protein was detected with differential protein abundance in the brains of trained bees, when compared to not trained ones, through computational gel imaging and statistical analysis. This protein was identified by peptide mass fingerprinting and MS/MS peptide fragmentation using a MALDI-TOF/TOF mass spectrometer as one isoform of arginine kinase monomer, apparently dephosphorylated. Brain protein maps were obtained by 2-DE (Two-dimensional gel electrophoresis) from a total proteins and phosphoproteins extract of the bee Melipona quadrifasciata. One isoform of arginine kinase, probably a dephosphorylated isoform, was significantly more abundant in the brain of trained bees using operant conditioning. Arginine kinase has been reported as an important enzyme of the energy releasing process in the visual system of the bee, but it may carry out additional and unexpected functions in the bee brain for learning process.

Increased survival of honey bees consuming pollen and beebread is associated with elevated biomarkers of oxidative stress

Introduction

Significant losses of honey bee colonies have been observed worldwide in recent decades. Inadequate nutrition is considered to be one of the factors that can reduce honey bee resistance to abiotic and biotic environmental stresses. Accordingly, we assessed the impact of food composition on worker bee survival.

Methods

Bees in cages were fed six different diets, and then their survival, levels of thiobarbituric acid reactive substances and protein carbonyl groups, catalase and lysozyme activities were evaluated.

Results and Discussion

After 17 days of feeding, the lowest mortality was observed in the group of bees that received sucrose solution with the addition of willow pollen or artificial rapeseed beebread or artificial willow beebread (diets 4–6). The highest mortality was found in bees that consumed only sucrose solution (diet 1) or the sucrose solution supplemented with a mixture of amino acids (diet 2), which can be explained by the lack of vitamins and microelements in these diets. In the group of bees that received the sucrose solution with rapeseed pollen (diet 3), mortality was intermediate. To check whether the decrease in insect survival could be related to oxidative damage, we evaluated biomarkers of oxidative stress. Consumption of pollen (diets 3 and 5) and artificial beebread (diets 4 and 6) enhances protein carbonylation in worker bees. Feeding bees artificial beebread also resulted in increase in lipid peroxidation and catalase activity, which is probably due to the presence of hydrogen peroxide in the honey contained in beebread. Remarkably, the increase in biomarkers of oxidative stress was not accompanied by adverse but positive effects on insect survival. A lack of amino acids and proteins in the diet 1 did not cause oxidative stress, but led to an increase in lysozyme activity in hemolymph, a biomarker of immune system status. In conclusion, we believe that the increase in oxidative stress biomarkers we found do not indicate oxidative damage, but rather reflect the changes in redox balance due to consumption of certain dietary options.

Evaluating the chronic effect of two varroacides using multiple biomarkers and an integrated biological response index

There is mounting evidence that acaricides are among the most prevalent medicinal compounds in honey bee hive matrices worldwide. According to OCDE guideline No. 245 chronic lethal concentration of tau-fluvalinate (at concentrations ranging from 77.5 to 523.18 ppm), coumaphos (59.8 ppm) and dimethoate (0.7 ppm) were determined. The activity of the biomarkers acetylcholinesterase (AChE), carboxylesterase (CbE), glutathione S-transferase (GST), catalase (CAT) and malondialdehyde (MDA) was analysed and as they are implicated in neurotoxicity, biotransformation and antioxidant defences, these values were combined into an integrated biomarker response (IBR). There was enhanced AChE, CAT and GST activity in honey bees exposed to tau-fluvalinate, while dimethoate inhibited AChE activity. Both dimethoate and coumaphos inhibited CbE activity but they enhanced CAT activity and MDA formation. Our results highlight how these biomarkers may serve to reveal honey bee exposure to commonly used acaricides.

Do the different life history strategies of ants and honeybees determine fat body morphology?

The separation of two sister groups such as ants and bees in the Cretaceous involved the development of distinctive characteristics to occupy separate ecological niches. From the point of view of biology and ecology, it is important to see how different life history strategies affect the physiology of these insects. The fat body is the most metabolically important tissue in the organism of each insect. Therefore, we conducted a comparative analysis of the morphological image of the subcuticular fat body in different localisation/segments in Formica (Seviformica) cinerea and Apis mellifera mellifera foragers, because of the similarity of their functions in colonies. We observed that the fat bodies of ants and bees were composed of the same cell types: trophocytes and oenocytes. However, in each of the segments, the fat body cells in ants were bigger and there were fewer of them in comparison with bees. The dorsal part of the fat body of ants had a bilayer structure, where the outer layer was formed by binucleated oenocytes. Binucleated oenocytes were also found in the inner layer near the heart and tracheole. In bees, the fat body was unilayered and the trophocytes and oenocytes were present side by side. The similarities and, in particular, the differences in the structure of the fat body are the adaptation of these sister groups to life in a diverse environment.

Worker bees (Apis mellifera) deprived of pollen in the first week of adulthood exhibit signs of premature aging

Pollinator populations, including bees, are in rapid decline in many parts of the world, raising concerns over the future of ecosystems and food production. Among the factors involved in these declines, poor nutrition deserves attention. The diet consumed by adult worker honeybees (Apis mellifera) is crucial for their behavioral maturation, i.e., the progressive division of labor they perform, such as nurse bees initially and later in life as foragers. Poor pollen nutrition is known to reduce the workers' lifespan, but the underlying physiological and genetic mechanisms are not fully understood. Here we investigate how the lack of pollen in the diet of workers during their first week of adult life can affect age-related phenotypes. During the first seven days of adult life, newly emerged workers were fed either a pollen-deprived (PD) diet mimicking that of an older bee, or a control pollen-rich (PR) diet, as typically consumed by young bees. The PD-fed bees showed alterations in their fat body transcriptome, such as a switch from a protein-lipid based metabolism to a carbohydrate-based metabolism, and a reduced expression of genes involved with immune response. The absence of pollen in the diet also led to an accumulation of oxidative stress markers in fat body tissue and alterations in the cuticular hydrocarbon profiles, which became similar to those of chronologically older bees. Together, our data indicate that the absence of pollen during first week of adulthood triggers the premature onset of an aging-related worker phenotype.

Exoskeleton ageing and its relation to longevity and fecundity in female Australian leaf insects (

Senescence is a decline in reproduction and survival rate with advancing age resulting from deterioration of somatic tissues and systems throughout the body. Age-related somatic changes (somatic ageing) have been studied extensively in vertebrates but are less well known in other animals, including insects. Since adult insects have very limited ability to repair their exoskeleton, somatic ageing could involve deterioration and discolouration of the cuticle. We investigated age-related changes in wing pigmentation and abdominal cuticle necrosis in females of the Australian leaf insect Phyllium monteithi. Adult females varied markedly in the extent and pattern of pigmentation on their bodies, and we found that pigment spots on the forewings increased in size with age in most individuals. As females aged, most individuals also exhibited increasing levels of abdominal cuticle necrosis, resulting in the loss of abdominal cuticle along the margin of the abdomen. Neither the extent of pigmentation nor cuticle loss were clearly associated with reduced fecundity or longevity in the protected laboratory environment, but it remains unknown whether these age-related changes have functional implications in the wild. Our results show that the P. monteithi exoskeleton undergoes complex changes with age, with potential implications for functional traits and fitness.

Context-dependent influence of threat on honey bee social network dynamics and brain gene expression

Adverse social experience affects social structure by modifying the behavior of individuals, but the relationship between an individual's behavioral state and its response to adversity is poorly understood. We leveraged naturally occurring division of labor in honey bees and studied the biological embedding of environmental threat using laboratory assays and automated behavioral tracking of whole colonies. Guard bees showed low intrinsic levels of sociability compared with foragers and nurse bees, but large increases in sociability following exposure to a threat. Threat experience also modified the expression of caregiving-related genes in a brain region called the mushroom bodies. These results demonstrate that the biological embedding of environmental experience depends on an individual's societal role and, in turn, affects its future sociability.

Middle-Aged Worker Bees Express Higher Innate Immunity than Young Worker Bees in the Abdomen without the Digestive Tract of Worker Bees Reared in an Incubator

Honey bees (Apis mellifera) can be reared in an incubator to study the mechanisms of aging and longevity; however, whether breeding in an incubator and using the abdomen without the digestive tract influences the expression of immune genes is unclear. In this study, we assayed the immune genes including abaecin, hymenoptaecin, defensin-2, glucose dehydrogenase, phenoloxidase, and lysozyme from the whole body of young and middle-aged worker bees reared in field hives, the whole body of young and middle-aged worker bees reared in a 34 °C incubator, and the abdomen without the digestive tract of young and middle-aged worker bees reared in a 34 °C incubator. The results showed that three groups of middle-aged worker bees have higher immunity than young worker bees. Furthermore, the similarity of immune genes expression in three groups indicated that the abdomen without the digestive tract of honey bees reared in an incubator can be used to study the relationship between immunity and aging and longevity to avoid the interference of pathogens and parasites from field hives.

The Biology of Aging in Insects: From Drosophila to Other Insects and Back

An enormous amount of work has been done on aging in Drosophila melanogaster, a classical genetic and molecular model system, but also in numerous other insects. However, these two extensive bodies of work remain poorly integrated to date. Studies in Drosophila often explore genetic, developmental, physiological, and nutrition-related aspects of aging in the lab, while studies in other insects often explore ecological, social, and somatic aspects of aging in both lab and natural populations. Alongside exciting genomic and molecular research advances in aging in Drosophila, many new studies have also been published on aging in various other insects, including studies on aging in natural populations of diverse species. However, no broad synthesis of these largely separate bodies of work has been attempted. In this review, we endeavor to synthesize these two semi-independent literatures to facilitate collaboration and foster the exchange of ideas and research tools. While lab studies of Drosophila have illuminated many fundamental aspects of senescence, the stunning diversity of aging patterns among insects, especially in the context of their rich ecology, remains vastlyunderstudied. Coupled with field studies and novel, more easily applicable molecular methods, this represents a major opportunity for deepening our understanding of the biology of aging in insects and beyond.

Regulation of membrane phospholipids during the adult life of worker honey bee

Two female castes that are genetically identical are found in honey bees: workers and queens. Adult female honey bees differ in their morphology and behaviors, but the most intriguing difference between the castes is the difference in their longevity. Queens live for years while workers live generally for weeks. The mechanisms that mediate this extraordinary difference in lifespan remain mostly unknown. Both castes share similar developmental stages and are fed liquid food (i.e. a jelly) during development. However, after emergence, workers begin to feed on pollen while queens are fed the same larval food for their entire life. Pollen has a high content of polyunsaturated fatty acids (PUFA) while royal jelly has negligible amounts. The difference in food during adult life leads to drastic changes in membrane phospholipids of female honey bees, and those changes have been proposed as mechanisms that could explain the difference in lifespan. To provide further details on those mechanisms, we characterized the membrane phospholipids of adult workers at seven different ages covering all life-history stages. Our results suggest that the majority of changes in worker membranes occur in the first four days of adult life. Shortly after emergence, workers increase their level of total phospholipids by producing phospholipids that contained saturated (SFA) and monounsaturated fatty acids (MUFA). From the second day, workers start replacing fatty acid chains from those pre-synthesized molecules with PUFA acquired from pollen. After four days, worker membranes are set and appear to be maintained for the rest of adult life, suggesting that damaged PUFA are replaced effectively. Plasmalogen phospholipids increase continuously throughout worker adult life, suggesting that plasmalogen might help to reduce lipid peroxidation in worker membranes. We postulate that the diet-induced increase in PUFA in worker membranes makes them far more prone to lipid-based oxidative damage compared to queens.

Chemical Stimulants and Stressors Impact the Outcome of Virus Infection and Immune Gene Expression in Honey Bees (Apis mellifera)

Western honey bees (Apis mellifera) are ecologically, agriculturally, and economically important plant pollinators. High average annual losses of honey bee colonies in the US have been partially attributed to agrochemical exposure and virus infections. To examine the potential negative synergistic impacts of agrochemical exposure and virus infection, as well as the potential promise of phytochemicals to ameliorate the impact of pathogenic infections on honey bees, we infected bees with a panel of viruses (i.e., Flock House virus, deformed wing virus, or Sindbis virus) and exposed to one of three chemical compounds. Specifically, honey bees were fed sucrose syrup containing: (1) thyme oil, a phytochemical and putative immune stimulant, (2) fumagillin, a beekeeper applied fungicide, or (3) clothianidin, a grower-applied insecticide. We determined that virus abundance was lower in honey bees fed 0.16 ppb thyme oil augmented sucrose syrup, compared to bees fed sucrose syrup alone. Parallel analysis of honey bee gene expression revealed that honey bees fed thyme oil augmented sucrose syrup had higher expression of key RNAi genes (argonaute-2 and dicer-like), antimicrobial peptide expressing genes (abaecin and hymenoptaecin), and vitellogenin, a putative honey bee health and age indicator, compared to bees fed only sucrose syrup. Virus abundance was higher in bees fed fumagillin (25 ppm or 75 ppm) or 1 ppb clothianidin containing sucrose syrup relative to levels in bees fed only sucrose syrup. Whereas, honey bees fed 10 ppb clothianidin had lower virus levels, likely because consuming a near lethal dose of insecticide made them poor hosts for virus infection. The negative impact of fumagillin and clothianidin on honey bee health was indicated by the lower expression of argonaute-2, dicer-like, abaecin, and hymenoptaecin, and vitellogenin. Together, these results indicate that chemical stimulants and stressors impact the outcome of virus infection and immune gene expression in honey bees.

An Expanded Survey of the Moth PBP/GOBP Clade in Bombyx mori: New Insight into Expression and Functional Roles

We studied the expression profile and ontogeny (from the egg stage through the larval stages and pupal stages, to the elderly adult age) of four OBPs from the silkworm moth Bombyx mori. We first showed that male responsiveness to female sex pheromone in the silkworm moth B. mori does not depend on age variation; whereas the expression of BmorPBP1, BmorPBP2, BmorGOBP1, and BmorGOBP2 varies with age. The expression profile analysis revealed that the studied OBPs are expressed in non-olfactory tissues at different developmental stages. In addition, we tested the effect of insecticide exposure on the expression of the four OBPs studied. Exposure to a toxic macrolide insecticide endectocide molecule (abamectin) led to the modulated expression of all four genes in different tissues. The higher expression of OBPs was detected in metabolic tissues, such as the thorax, gut, and fat body. All these data strongly suggest some alternative functions for these proteins other than olfaction. Finally, we carried out ligand docking studies and reported that PBP1 and GOBP2 have the capacity of binding vitamin K1 and multiple different vitamins.

Reproductive Potential Impacts Body Maintenance Parameters and Global DNA Methylation in Honeybee Workers (Apis mellifera L.)

Simple Summary

The queens and sterile workers arise from genetically identical eggs but as imagoes, they differ in their life span, DNA methylation, and their functions. In the absence of the queen, the larvae develop into rebels, i.e., workers with increased reproductive potential. We assumed that since rebels are similar to the queen in many anatomical and behavioral features, they live longer and have lower levels of global DNA methylation, even when infected, e.g., by Nosema spp. Rebels always lived longer in comparison in normal workers and unexpectedly extended longevity of normal workers when they were together, similarly as the presence of a queen did. Rebels became infected more easily but tolerated the infection better. They also had lower level of global DNA methylation than normal workers. These features expand possibilities of the use of honeybees as a model for studies on senescence, nosemosis, eusocial evolution, and epigenetics.

Abstract

The widely accepted hypothesis in life history evolution about the trade-off between fecundity and longevity is not confirmed by long-living and highly fecund queens in eusocial insects. The fact that the queens and facultatively sterile workers usually arise from genetically identical eggs but differ in DNA methylation makes them a good model for studies on senescence, eusocial evolution, and epigenetics. Therefore, honeybees seem to be especially useful here because of long living rebel-workers (RW) with high reproductive potential recently described. Longevity, ovariole number, nosema tolerance, and global DNA methylation have been assayed in normal workers (NW) versus RW in hives and cages. RW always lived longer than NW and unexpectedly extended longevity of NW when they were together, similarly as the presence of a queen did. RW lived longer despite the fact that they had higher Nosema spore load; surprisingly they became infected more easily but tolerated the infection better. Global DNA methylation increased with age, being lower in RW than in NW. Therefore, RW are queen-like considering global DNA methylation and the link between fecundity, longevity, and body maintenance. Presented features of RW expands possibilities of the use of honeybees as a model for studies on senescence, nosemosis, eusocial evolution, and epigenetics.

The molecular interplay of the establishment of an infection - gene expression of Diaphorina citri gut and Candidatus Liberibacter asiaticus

BACKGROUND

Candidatus Liberibacter asiaticus (CLas) is one the causative agents of greening disease in citrus, an unccurable, devastating disease of citrus worldwide. CLas is vectored by Diaphorina citri, and the understanding of the molecular interplay between vector and pathogen will provide additional basis for the development and implementation of successful management strategies. We focused in the molecular interplay occurring in the gut of the vector, a major barrier for CLas invasion and colonization.

RESULTS

We investigated the differential expression of vector and CLas genes by analyzing a de novo reference metatranscriptome of the gut of adult psyllids fed of CLas-infected and healthy citrus plants for 1-2, 3-4 and 5-6 days. CLas regulates the immune response of the vector affecting the production of reactive species of oxygen and nitrogen, and the production of antimicrobial peptides. Moreover, CLas overexpressed peroxiredoxin, probably in a protective manner. The major transcript involved in immune expression was related to melanization, a CLIP-domain serine protease we believe participates in the wounding of epithelial cells damaged during infection, which is supported by the down-regulation of pangolin. We also detected that CLas modulates the gut peristalsis of psyllids through the down-regulation of titin, reducing the elimination of CLas with faeces. The up-regulation of the neuromodulator arylalkylamine N-acetyltransferase implies CLas also interferes with the double brain-gut communication circuitry of the vector. CLas colonizes the gut by expressing two Type IVb pilin flp genes and several chaperones that can also function as adhesins. We hypothesized biofilm formation occurs by the expression of the cold shock protein of CLas.

CONCLUSIONS

The thorough detailed analysis of the transcritome of Ca. L. asiaticus and of D. citri at different time points of their interaction in the gut tissues of the host led to the identification of several host genes targeted for regulation by L. asiaticus, but also bacterial genes coding for potential effector proteins. The identified targets and effector proteins are potential targets for the development of new management strategies directed to interfere with the successful utilization of the psyllid vector by this pathogen.

Screening of Dietary Ingredients against the Honey Bee Parasite Nosema ceranae

Nosema ceranae is a major pathogen in the beekeeping sector, responsible for nosemosis. This disease is hard to manage since its symptomatology is masked until a strong collapse of the colony population occurs. Conversely, no medicaments are available in the market to counteract nosemosis, and only a few feed additives, with claimed antifungal action, are available. New solutions are strongly required, especially based on natural methods alternative to veterinary drugs that might develop resistance or strongly pollute honey bees and the environment. This study aims at investigating the nosemosis antiparasitic potential of some plant extracts, microbial fermentation products, organic acids, food chain waste products, bacteriocins, and fungi. Honey bees were singularly infected with 5 × 104 freshly prepared N. ceranae spores, reared in cages and fed ad libitum with sugar syrup solution containing the active ingredient. N. ceranae in the gut of honey bees was estimated using qPCR. The results showed that some of the ingredients administered, such as acetic acid at high concentration, p-coumaric acid, and Saccharomyces sp. strain KIA1, were effective in the control of nosemosis. On the other hand, wine acetic acid strongly increased the N. ceranae amount. This study investigates the possibility of using compounds such as organic acids or biological agents including those at the base of the circular economy, i.e., wine waste production, in order to improve honeybee health.

Segmentation of the subcuticular fat body in Apis mellifera females with different reproductive potentials

Evolution has created different castes of females in eusocial haplodiploids. The difference between them lies in their functions and vulnerability but above all in their reproductive potentials. Honeybee queens are highly fertile. On the other hand, the workers are facultatively sterile. However, rebel workers, i.e. workers that develop in a queenless colony, reproduce more often than normal workers. As a result, the fat body of these bees, which apart from acting as the energy reserve, is also the site of numerous metabolic processes, had to specialize in different functions perfected over millions of years of eusocial evolution. Assuming that the variety of functions manifests itself in the pleomorphic structure of the fat body cells, we predicted that also different parts of the fat body, e.g. from different segments of the abdomen, contain different sets of cells. Such differences could be expected between queens, rebels and normal workers, i.e. females with dramatically different reproductive potentials. We confirmed all these expectations. Although all bees had the same types of cells, their proportion and segmental character corresponded with the caste reproductive potential and physiological characteristics shaped in the evolutionary process. The females with an increased reproductive potential were characterized by the presence of oenocytes in the third tergite and high concentrations of compounds responsible for energy reserves, like glucose, glycogen and triglycerides. Queens had very large trophocytes, especially in the third tergite. Only in workers did we observe intercellular spaces in all the segments of the fat body, as well as high protein concentrations-especially in the sternite. As expected, the rebels combined many features of the queens and normal workers, what with other findings can help understand the ways that led to the origin of different castes in females of eusocial Hymenoptera.

Disentangling the aging gene expression network of termite queens

Background

Most insects are relatively short-lived, with a maximum lifespan of a few weeks, like the aging model organism, the fruit-fly Drosophila melanogaster. By contrast, the queens of many social insects (termites, ants and some bees) can live from a few years to decades. This makes social insects promising models in aging research providing insights into how a long reproductive life can be achieved. Yet, aging studies on social insect reproductives are hampered by a lack of quantitative data on age-dependent survival and time series analyses that cover the whole lifespan of such long-lived individuals. We studied aging in queens of the drywood termite Cryptotermes secundus by determining survival probabilities over a period of 15 years and performed transcriptome analyses for queens of known age that covered their whole lifespan.

Results

The maximum lifespan of C. secundus queens was 13 years, with a median maximum longevity of 11.0 years. Time course and co-expression network analyses of gene expression patterns over time indicated a non-gradual aging pattern. It was characterized by networks of genes that became differentially expressed only late in life, namely after ten years, which associates well with the median maximum lifespan for queens. These old-age gene networks reflect processes of physiological upheaval. We detected strong signs of stress, decline, defense and repair at the transcriptional level of epigenetic control as well as at the post-transcriptional level with changes in transposable element activity and the proteostasis network. The latter depicts an upregulation of protein degradation, together with protein synthesis and protein folding, processes which are often down-regulated in old animals. The simultaneous upregulation of protein synthesis and autophagy is indicative of a stress-response mediated by the transcription factor cnc, a homolog of human nrf genes.

Conclusions

Our results show non-linear senescence with a rather sudden physiological upheaval at old-age. Most importantly, they point to a re-wiring in the proteostasis network and stress as part of the aging process of social insect queens, shortly before queens die.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07649-4.

Oxidative stress and senescence in social insects: a significant but inconsistent link?

The life-prolonging effects of antioxidants have long entered popular culture, but the scientific community still debates whether free radicals and the resulting oxidative stress negatively affect longevity. Social insects are intriguing models for analysing the relationship between oxidative stress and senescence because life histories differ vastly between long-lived reproductives and the genetically similar but short-lived workers. Here, we present the results of an experiment on the accumulation of oxidative damage to proteins, and a comparative analysis of the expression of 20 selected genes commonly involved in managing oxidative damage, across four species of social insects: a termite, two bees and an ant. Although the source of analysed tissue varied across the four species, our results suggest that oxidative stress is a significant factor in senescence and that its manifestation and antioxidant defenses differ among species, making it difficult to find general patterns. More detailed and controlled investigations on why responses to oxidative stress may differ across social species may lead to a better understanding of the relations between oxidative stress, antioxidants, social life history and senescence. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Queen loss increases worker survival in leaf-cutting ants under paraquat-induced oxidative stress

Longevity is traded off with fecundity in most solitary species, but the two traits are positively linked in social insects. In ants, the most fecund individuals (queens and kings) live longer than the non-reproductive individuals, the workers. In many species, workers may become fertile following queen loss, and recent evidence suggests that worker fecundity extends worker lifespan. We postulated that this effect is in part owing to improved resilience to oxidative stress, and tested this hypothesis in three Myrmicine ants: Temnothorax rugatulus, and the leaf-cutting ants Atta colombica and Acromyrmex echinatior. We removed the queen from colonies to induce worker reproduction and subjected workers to oxidative stress. Oxidative stress drastically reduced survival, but this effect was less pronounced in leaf-cutting ant workers from queenless nests. We also found that, irrespective of oxidative stress, outside workers died earlier than inside workers did, likely because they were older. Since At. colombica workers cannot produce fertile offspring, our results indicate that direct reproduction is not necessary to extend the lives of queenless workers. Our findings suggest that workers are less resilient to oxidative stress in the presence of the queen, and raise questions on the proximate and ultimate mechanisms underlying socially mediated variation in worker lifespan. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Antioxidation Defenses of Apis mellifera Queens and Workers Respond to Imidacloprid in Different Age-Dependent Ways: Old Queens Are Resistant, Foragers Are Not

Simple Summary

Honey bees are unique for studies on aging because queens live 40-fold longer than workers. An efficient antioxidant defense (ADS) is thought to be pivotal for longevity, but not always. How were different ADSs shaped by evolution in young and old queens and workers? Honey bees, the essential pollinators, are facing depopulation due, at least in part, to pesticides, such as imidacloprid, an oxidative stressor. Is an evolutionarily shaped ADS still useful for contemporary young and old queens/workers? Answering these questions is important for emerging oxidative-stress ecology and protecting contemporary honey bees. The ADS activity was determined in 1-day-old, 20-day-old, and 2-year-old queens and in 1-day-old and 20-day-old workers (foragers) fed without (control) or with low or high imidacloprid (in bee food). ADS was upregulated in workers with age but downregulated in queens. However, imidacloprid oxidative stress suppressed the active ADS in workers, particularly 20-day-old foragers, but not in 1-day-old queens. Unexpectedly, poor ADS activity in 2-year-old queens was highly upregulated by imidacloprid. Thus, queen and worker ADSs respond to imidacloprid in opposite ways, and old queens were still resistant, but foragers were not. This may be unfavorable for foragers dwelling in ecosystems that expose them to pesticides.

Abstract

We investigated how different antioxidant defenses (ADSs) were shaped by evolution in young/old Apis mellifera workers and queens to broaden the limited knowledge on whether ADSs are effective in contemporary pesticide environments and to complete bee oxidative-aging theory. We acquired 1-day-old, 20-day-old, and 2-year-old queens and 1-day-old and 20-day-old workers (foragers) fed 0, 5, or 200 ppb imidacloprid, a pesticide oxidative stressor. The activities of catalase, glutathione peroxidase, glutathione S-transferase, and superoxide dismutase and the level of total antioxidant potential were determined in hemolymph. The ADS was upregulated in workers with age but downregulated in queens. Imidacloprid suppressed the ADS in all workers, particularly in foragers with an upregulated ADS, but it did not affect the ADS in 1-day-old queens. In contrast to foragers, the downregulated ADS of 2-year-old queens was unexpectedly highly upregulated by imidacloprid, which has not been previously shown in such old queens. The principal component analysis confirmed that queen and worker ADSs responded to imidacloprid in opposite ways, and ADS of 2-year-queens was markedly different from those of others. Thus, evolutionary shaped ADSs of older queens and workers may be of the limited use for foragers dwelling in pesticide ecosystems, but not for old queens.

Social networks predict the life and death of honey bees

In complex societies, individuals' roles are reflected by interactions with other conspecifics. Honey bees (Apis mellifera) generally change tasks as they age, but developmental trajectories of individuals can vary drastically due to physiological and environmental factors. We introduce a succinct descriptor of an individual's social network that can be obtained without interfering with the colony. This 'network age' accurately predicts task allocation, survival, activity patterns, and future behavior. We analyze developmental trajectories of multiple cohorts of individuals in a natural setting and identify distinct developmental pathways and critical life changes. Our findings suggest a high stability in task allocation on an individual level. We show that our method is versatile and can extract different properties from social networks, opening up a broad range of future studies. Our approach highlights the relationship of social interactions and individual traits, and provides a scalable technique for understanding how complex social systems function.

Winter honeybee (Apis mellifera) populations show greater potential to induce immune responses than summer populations after immune stimuli

In the temperate climates of central Europe and North America, two distinct honeybee (Apis mellifera) populations are found in colonies: short-living summer bees emerge in spring and survive until summer, whereas long-living winter bees emerge in late August and overwinter. Besides the difference in their life spans, each of these populations fulfils a different role in the colonies and individual bees have distinct physiological and immunological adaptations depending on their roles. For instance, winter worker bees have higher vitellogenin levels and larger reserves of nutrients in the fat body than summer bees. The differences between the immune systems of both populations are well described at the constitutive level; however, our knowledge of its inducibility is still very limited. In this study, we focus on the response of 10-day-old honeybee workers to immune challenges triggered in vivo by injecting heat-killed bacteria, with particular focus on honeybees that emerge and live under hive conditions. Responses to bacterial injections differed between summer and winter bees. Winter bees exhibited a more intense response, including higher expression of antimicrobial genes and antimicrobial activity, as well as a significant decrease in vitellogenin gene expression and its concentration in the hemolymph. The intense immune response observed in winter honeybees may contribute to our understanding of the relationships between colony fitness and infection with pathogens, as well as its association with successful overwintering.

Honeybee lifespan: the critical role of pre-foraging stage

Assessing the various anthropogenic pressures imposed on honeybees requires characterizing the patterns and drivers of natural mortality. Using automated lifelong individual monitoring devices, we monitored worker bees in different geographical, seasonal and colony contexts creating a broad range of hive conditions. We measured their life-history traits and notably assessed whether lifespan is influenced by pre-foraging flight experience. Our results show that the age at the first flight and onset of foraging are critical factors that determine, to a large extent, lifespan. Most importantly, our results indicate that a large proportion (40%) of the bees die during pre-foraging stage, and for those surviving, the elapsed time and flight experience between the first flight and the onset of foraging is of paramount importance to maximize the number of days spent foraging. Once in the foraging stage, individuals experience a constant mortality risk of 9% and 36% per hour of foraging and per foraging day, respectively. In conclusion, the pre-foraging stage during which bees perform orientation flights is a critical driver of bee lifespan. We believe these data on the natural mortality risks in honeybee workers will help assess the impact of anthropogenic pressures on bees.

Special Significance of Non-Drosophila Insects in Aging

Aging is the leading risk factor of human chronic diseases. Understanding of aging process and mechanisms facilitates drug development and the prevention of aging-related diseases. Although many aging studies focus on fruit fly as a canonical insect system, minimal attention is paid to the potentially significant roles of other insects in aging research. As the most diverse group of animals, insects provide many aging types and important complementary systems for aging studies. Insect polyphenism represents a striking example of the natural variation in longevity and aging rate. The extreme intraspecific variations in the lifespan of social insects offer an opportunity to study how aging is differentially regulated by social factors. Insect flight, as an extremely high-intensity physical activity, is suitable for the investigation of the complex relationship between metabolic rate, oxidative stress, and aging. Moreover, as a "non-aging" state, insect diapause not only slows aging process during diapause phase but also affects adult longevity during/after diapause. In the past two decades, considerable progress has been made in understanding the molecular basis of aging regulation in insects. Herein, the recent research progress in non-Drosophila insect aging was reviewed, and its potential utilization in aging in the future was discussed.

Thiacloprid exposure perturbs the gut microbiota and reduces the survival status in honeybees

Honeybees (Apis mellifera) offer ecosystem services such as pollination, conservation of biodiversity, and provision of food. However, in recent years, the number of honeybee colonies is diminishing rapidly, which is probably linked to the wide use of neonicotinoid insecticides. Middle-aged honeybees were fed with 50% (w/v) sucrose solution containing 0, 0.2, 0.6, and 2.0 mg/L thiacloprid (a neonicotinoid insecticide) for up to 13 days, and on each day of exposure experiment, percentage survival, sucrose consumption, and bodyweight of honeybees were measured. Further, changes in honeybee gut microbial community were examined using next-generation 16S rDNA amplicon sequencing on day 1, 7, and 13 of the exposure. When compared to control-treatment, continuous exposure to high (0.6 mg/L) and very high (2.0 mg/L) concentrations of thiacloprid significantly reduced percentage survival of honeybees (p <  0.001) and led to dysbiosis of their gut microbial community on day 7 of the exposure. However, during subsequent developmental stages of middle-aged honeybees (i.e. on day 13), their gut microbiome recovered from dysbiosis that occurred previously due to thiacloprid exposure. Taken together, improper application of thiacloprid can cause loss of honeybee colonies, while the microbial gut community of honeybee is an independent variable in this process.

Longer life span is associated with elevated immune activity in a seasonally polyphenic butterfly

Seasonal polyphenism constitutes a specific type of phenotypic plasticity in which short-lived organisms produce different phenotypes in different times of the year. Seasonal generations of such species frequently differ in their overall lifespan and in the values of traits closely related to fitness. Seasonal polyphenisms provide thus excellent, albeit underused model systems for studying trade-offs between life-history traits. Here, we compare immunological parameters between the two generations of the European map butterfly (Araschnia levana), a well-known example of a seasonally polyphenic species. To reveal possible costs of immune defence, we also examine the concurrent differences in several life-history traits. Both in laboratory experiments and in the field, last instar larvae heading towards the diapause (overwintering) had higher levels of both phenoloxidase (PO) activity and lytic activity than directly developing individuals. These results suggest that individuals from the diapausing generation with much longer juvenile (pupal) period invest more in their immune system than those from the short-living directly developing generation. The revealed negative correlation between pupal mass and PO activity may be one of the reasons why, in this species, the diapausing generation has a smaller body size than the directly developing generation. Immunological parameters may thus well mediate trade-offs between body size-related traits.

Long live the queen, the king and the commoner? Transcript expression differences between old and young in the termite Cryptotermes secundus

Social insects provide promising new avenues for aging research. Within a colony, individuals that share the same genetic background can differ in lifespan by up to two orders of magnitude. Reproducing queens (and in termites also kings) can live for more than 20 years, extraordinary lifespans for insects. We studied aging in a termite species, Cryptotermes secundus, which lives in less socially complex societies with a few hundred colony members. Reproductives develop from workers which are totipotent immatures. Comparing transcriptomes of young and old individuals, we found evidence for aging in reproductives that was especially associated with DNA and protein damage and the activity of transposable elements. By contrast, workers seemed to be better protected against aging. Thus our results differed from those obtained for social insects that live in more complex societies. Yet, they are in agreement with lifespan estimates for the study species. Our data are also in line with expectations from evolutionary theory. For individuals that are able to reproduce, it predicts that aging should only start after reaching maturity. As C. secundus workers are immatures with full reproductive options we expect them to invest into anti-aging processes. Our study illustrates that the degree of aging can differ between social insects and that it may be associated with caste-specific opportunities for reproduction.

Comb Irradiation Has Limited, Interactive Effects on Colony Performance or Pathogens in Bees, Varroa destructor and Wax Based on Two Honey Bee Stocks

Parasitic mites and pathogens compromise honey bee health. Development of sustainable and integrative methods of managing these problems will minimize their detrimental impact on honey bees. Here, we aimed to determine if the combination of using mite-resistant stocks along with gamma-irradiated combs influences colony health and productivity. The major finding concerned honey bee genotype confirming that Russian honey bees are more resistant to Varroa destructor than Italian honey bees. The effect of comb irradiation was inconsistent showing a significant increase in adult bee population and amount of stored pollen in 2015, but not in 2016. The increased amount of stored pollen was probably associated with larger adult population in colonies with irradiated combs in September 2015 regardless of honey bee stock. Nevertheless, the ability of bees to collect and store more pollen in the irradiated group does not appear to compensate the negative impacts of mite parasitism on honey bees especially in the Italian bees, which consistently suffered significant colony losses during both years. Results of viral analyses of wax, newly emerged bees, and Varroa and their pupal hosts showed common detections of Deformed wing virus (DWV), Varroa destructor virus (VDV-1), Chronic bee paralysis virus (CBPV), and Black queen cell virus (BQCV). Wax samples had on average ~4 viruses or pathogens detected in both irradiated and non-irradiated combs. Although pathogen levels varied by month, some interesting effects of honey bee stock and irradiation treatment were notable, indicating how traits of mite resistance and alternative treatments may have additive effects. Further, this study indicates that wax may be a transmission route of viral infection. In addition, pupae and their infesting mites from Italian colonies exhibited higher levels of DWV than those from Russian colonies suggesting potential DWV resistance by Russian honey bees. CBPV levels were also reduced in mites from Russian colonies in general and in mites, mite-infested pupae, and newly emerged bees that were collected from irradiated combs. However, BQCV levels were not reduced by comb irradiation. Overall, the contribution of irradiating comb in improving honey bee health and colony survival appears to be subtle, but may be useful as part of an integrated pest management strategy with the addition of using mite-resistant stocks.

Pollen reverses decreased lifespan, altered nutritional metabolism, and suppressed immunity in honey bees (Apis mellifera) treated with antibiotics

Nutrition is involved in regulating multiple aspects of honeybee biology such as caste, immunity, lifespan, growth and behavioral development. Deformed wing virus (DWV) is a major pathogenic factor which threatens honeybee populations, and its replication is regulated by nutrition status and immune responses of honeybees. The alimentary canal of the honeybee is home to a diverse microbial community that provides essential nutrients and serves to bolster immune responses. However, to what extent gut bacteria affect honeybee nutrition metabolism and immunity with respect to DWV has not been investigated fully. In this study, newly emerged worker bees were subjected to four diets that contained 1) pollen, 2) pollen and antibiotics, 3) neither pollen nor antibiotics, 4) antibiotics alone. The expression level of two nutrition genes target of rapamycin (tor) and insulin like peptide (ilp1), one nutritional marker gene vitellogenin (vg), five major royal jelly proteins genes (mrjp1-5), one antimicrobial peptide regulating gene relish (rel), and DWV virus titer and its replication intermediate, negative RNA strand, were determined by qRT-PCR from the honeybees after 7 days post antibiotic treatment. Additionally, honeybee head weight and survival rate were measured. We observed that antibiotics decreased the expression of tor and rel, increased DWV titer and its replication activity. Expression of ilp1, five mrjps, vg, and honeybee head weight were also reduced compared to bees on a pollen diet. Antibiotics also caused a significant drop in survivorship, which could be rescued by addition of pollen to diets. Of importance, pollen could partially rescue the loss of vg and mrjp2 while also increasing head weight of antibiotic-treated bees. Our results illuminate the roles of bacteria in honeybee nutrition, metabolism, and immunity; which confer the capability of inhibiting virus replication, extending honeybee lifespan, and improving overall health.

Measuring biological age to assess colony demographics in honeybees

Honeybee colonies are increasingly exposed to environmental stress factors, which can lead to their decline or failure. However, there are major gaps in stressor risk assessment due to the difficulty of assessing the honeybee colony state and detecting abnormal events. Since stress factors usually induce a demographic disturbance in the colony (e.g. loss of foragers, early transition from nurse to forager state), we suggest that disturbances could be revealed indirectly by measuring the age- and task-related physiological state of bees, which can be referred to as biological age (an indicator of the changes in physiological state that occur throughout an individual lifespan). We therefore estimated the biological age of bees from the relationship between age and biomarkers of task specialization (vitellogenin and the adipokinetic hormone receptor). This relationship was determined from a calibrated sample set of known-age bees and mathematically modelled for biological age prediction. Then, we determined throughout the foraging season the evolution of the biological age of bees from colonies with low (conventional apiary) or high Varroa destructor infestation rates (organic apiary). We found that the biological age of bees from the conventional apiary progressively decreased from the spring (17 days) to the fall (6 days). However, in colonies from the organic apiary, the population aged from spring (13 days) to summer (18.5 days) and then rejuvenated in the fall (13 days) after Varroa treatment. Biological age was positively correlated with the amount of brood (open and closed cells) in the apiary with low Varroa pressure, and negatively correlated with Varroa infestation level in the apiary with high Varroa pressure. Altogether, these results show that the estimation of biological age is a useful and effective method for assessing colony demographic state and likely detrimental effects of stress factors.

Honey bees overwintering in a southern climate: longitudinal effects of nutrition and queen age on colony-level molecular physiology and performance

Honey bee colony nutritional ecology relies on the acquisition and assimilation of floral resources across a landscape with changing forage conditions. Here, we examined the impact of nutrition and queen age on colony health across extended periods of reduced forage in a southern climate. We measured conventional hive metrics as well as colony-level gene expression of eight immune-related genes and three recently identified homologs of vitellogenin (vg), a storage glycolipoprotein central to colony nutritional state, immunity, oxidative stress resistance and life span regulation. Across three apiary sites, concurrent longitudinal changes in colony-level gene expression and nutritional state reflected the production of diutinus (winter) bees physiologically altered for long-term nutrient storage. Brood production by young queens was significantly greater than that of old queens, and was augmented by feeding colonies supplemental pollen. Expression analyses of recently identified vg homologs (vg-like-A, -B, and -C) revealed distinct patterns that correlated with colony performance, phenology, and immune-related gene transcript levels. Our findings provide new insights into dynamics underlying managed colony performance on a large scale. Colony-level, molecular physiological profiling is a promising approach to effectively identify factors influencing honey bee health in future landscape and nutrition studies.

Antennal Protein Profile in Honeybees: Caste and Task Matter More Than Age

Reproductive and task partitioning in large colonies of social insects suggest that colony members belonging to different castes or performing different tasks during their life (polyethism) may produce specific semiochemicals and be differently sensitive to the variety of pheromones involved in intraspecific chemical communication. The main peripheral olfactory organs are the antennal chemosensilla, where the early olfactory processes take place. At this stage, members of two different families of soluble chemosensory proteins [odorant-binding proteins (OBPs) and chemosensory proteins (CSPs)] show a remarkable affinity for different odorants and act as carriers while a further family, the Niemann-Pick type C2 proteins (NPC2) may have a similar function, although this has not been fully demonstrated. Sensillar lymph also contains Odorant degrading enzymes (ODEs) which are involved in inactivation through degradation of the chemical signals, once the message is conveyed. Despite their importance in chemical communication, little is known about how proteins involved in peripheral olfaction and, more generally antennal proteins, differ in honeybees of different caste, task and age. Here, we investigate for the first time, using a shotgun proteomic approach, the antennal profile of honeybees of different castes (queens and workers) and workers performing different tasks (nurses, guards, and foragers) by controlling for the potential confounding effect of age. Regarding olfactory proteins, major differences were observed between queens and workers, some of which were found to be more abundant in queens (OBP3, OBP18, and NPC2-1) and others to be more abundant in workers (OBP15, OBP21, CSP1, and CSP3); while between workers performing different tasks, OBP14 was more abundant in nurses with respect to guards and foragers. Apart from proteins involved in olfaction, we have found that the antennal proteomes are mainly characterized by castes and tasks, while age has no effect on antennal protein profile. Among the main differences, the strong decrease in vitellogenins found in guards and foragers is not associated with age.

Mitigating effects of pollen during paraquat exposure on gene expression and pathogen prevalence in Apis mellifera L

Honey bee (Apis mellifera L.) populations have been experiencing notable mortality in Europe and North America. No single cause has been identified for these dramatic losses, but rather multiple interacting factors are likely responsible (such as pesticides, malnutrition, habitat loss, and pathogens). Paraquat is one of the most widely used non-selective herbicides, especially in developing countries. This herbicide is considered slightly toxic to honey bees, despite being reported as a highly effective inducer of oxidative stress in a wide range of living systems. Here, we test the effects of paraquat on the expression of detoxification and antioxidant-related genes, as well as on the dynamics of pathogen titers. Moreover, we tested the effects of pollen as mitigating factor to paraquat exposure. Our results show significant changes in the expression of several antioxidant-related and detoxification-related genes in the presence of paraquat, as well as an increase of pathogens titers. Finally, we demonstrate a mitigating effect of pollen through the up-regulation of specific genes and improvement of survival of bees exposed to paraquat. The presence of pollen in the diet was also correlated with a reduced prevalence of Nosema and viral pathogens. We discuss the importance of honey bees' nutrition, especially the availability of pollen, on colony losses chronically reported in the USA and Europe.

Honeybee workers with higher reproductive potential live longer lives

Social insects, especially honeybees, have received much attention in comparative gerontology because of their peculiar and flexible ageing patterns that differ across genetically similar individuals. The longevity of honeybee individuals varies and depends on patterns of gene expression during development; females developing into reproductive individuals (queens) live longer than facultatively sterile workers. Here, we show that rebel workers, which develop under queenless conditions after swarming and have high reproductive potential, live approximately 4days longer in hives and approximately 3days longer in cages than individuals that develop in queenright colonies and have lower reproductive potential; this difference in longevity occurs in both free-flying and caged workers. Moreover, we show that both rebel and normal workers live longer when their ovaries contain more ovarioles. Longer-living rebel workers can benefit the colony because they can fill the generation gap that emerges between workers after queen exchange during swarming. Our findings provide novel evidence that the fecundity of workers in a social insect colony impacts their intrinsic longevity.

Insights into the biochemical defence and methylation of the solitary bee Osmia rufa L: A foundation for examining eusociality development

We examined age-related biochemical and histological changes in the fat bodies and hemolymph of Osmia rufa males and females. We analysed solitary bees during diapause, in October and in April; as well as the flying insects following diapause, in May and June. The trophocyte sizes, as well as the numbers of lipid droplets were the greatest at the beginning of diapause. Subsequently, they decreased along with age. Triglyceride and glucose concentrations systematically decreased in fat body cells but increased in the hemolymph from October to June. Concentrations/activities of (enzymatic and non-enzymatic) antioxidant and proteolytic systems, as well as phenoloxidase, aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase levels were constant during the diapause, usually lower in the males than the females. Prior to the diapause/overwintering, the concentrations/activities of all the compounds were higher in the fat bodies than in the hemolymph. Later in the spring and in the summer, they increased in the hemolymph and on the body surfaces, while decreasing in the fat bodies. The global DNA methylation levels increased with age. Higher levels were always observed in the males than in the females. The study will promote better understanding of bee evolution and will be useful for the protection and management of solitary bees, with benefits to the environment and agriculture.

Weight of evidence evaluation of a network of adverse outcome pathways linking activation of the nicotinic acetylcholine receptor in honey bees to colony death

Ongoing honey bee (Apis mellifera) colony losses are of significant international concern because of the essential role these insects play in pollinating crops. Both chemical and non-chemical stressors have been implicated as possible contributors to colony failure; however, the potential role(s) of commonly-used neonicotinoid insecticides has emerged as particularly concerning. Neonicotinoids act on the nicotinic acetylcholine receptors (nAChRs) in the central nervous system to eliminate pest insects. However, mounting evidence indicates that neonicotinoids also may adversely affect beneficial pollinators, such as the honey bee, via impairments on learning and memory, and ultimately foraging success. The specific mechanisms linking activation of the nAChR to adverse effects on learning and memory are uncertain. Additionally, clear connections between observed impacts on individual bees and colony level effects are lacking. The objective of this review was to develop adverse outcome pathways (AOPs) as a means to evaluate the biological plausibility and empirical evidence supporting (or refuting) the linkage between activation of the physiological target site, the nAChR, and colony level consequences. Potential for exposure was not a consideration in AOP development and therefore this effort should not be considered a risk assessment. Nonetheless, development of the AOPs described herein has led to the identification of research gaps which, for example, may be of high priority in understanding how perturbation of pathways involved in neurotransmission can adversely affect normal colony functions, causing colony instability and subsequent bee population failure. A putative AOP network was developed, laying the foundation for further insights as to the role of combined chemical and non-chemical stressors in impacting bee populations. Insights gained from the AOP network assembly, which more realistically represents multi-stressor impacts on honey bee colonies, are promising toward understanding common sensitive nodes in key biological pathways and identifying where mitigation strategies may be focused to reduce colony losses.

Stress response in honeybees is associated with changes in task-related physiology and energetic metabolism

In a rapidly changing environment, honeybee colonies are increasingly exposed to diverse sources of stress (e.g., new parasites, pesticides, climate warming), which represent a challenge to individual and social homeostasis. However, bee physiological responses to stress remain poorly understood. We therefore exposed bees specialised in different tasks (nurses, guards and foragers) to ancient (immune and heat stress) or historically more recent sources of stress (pesticides), and we determined changes in the expression of genes linked to behavioural maturation (vitellogenin - vg and juvenile hormone esterase - jhe) as well as in energetic metabolism (glycogen level, expression level of the receptor to the adipokinetic hormone - akhr, and endothermic performance). While acute exposure to sublethal doses of two pesticides did not affect vg and jhe expression, immune and heat challenges caused a decrease and increase in both genes, respectively, suggesting that bees had responded to ecologically relevant stressors. Since vg and jhe are expressed to a higher level in nurses than in foragers, it is reasonable to assume that an immune challenge stimulated behavioural maturation to decrease potential contamination risk and that a heat challenge promoted a nurse profile for brood thermoregulation. All behavioural castes responded in the same way. Though endothermic performances did not change upon stress exposure, the akhr level dropped in immune and heat-challenged individuals. Similarly, the abdomen glycogen level tended to decline in immune-challenged bees. Altogether, these results suggest that bee responses are stress specific and adaptive but that they tend to entail a reduction of energetic metabolism that needs to be studied on a longer timescale.

Worker lifespan is an adaptive trait during colony establishment in the long-lived ant Lasius niger

Eusociality has been recognized as a strong driver of lifespan evolution. While queens show extraordinary lifespans of 20years and more, worker lifespan is short and variable. A recent comparative study found that in eusocial species with larger average colony sizes the disparities in the lifespans of the queen and the worker are also greater, which suggests that lifespan might be an evolved trait. Here, we tested whether the same pattern holds during colony establishment: as colonies grow larger, worker lifespan should decrease. We studied the mortality of lab-reared Lasius niger workers from colonies at two different developmental stages (small and intermediate-sized) in a common garden experiment. Workers were kept in artificial cohorts that differed only with respect to the stage of the colony they were born in. We found that the stage of the birth colony affected the body size and the survival probability of the workers. The workers that had emerged from early stage colonies were smaller and had lower mortality during the first 400days of their life than the workers born in colonies at a later stage. Our results suggest that early stage colonies produce small workers with an increased survival probability. These workers are gradually augmented by larger workers with a decreased survival probability that serve as a redundant workforce with easily replaceable individuals. We doubt that the observed differences in lifespan are driven by differences in body size. Rather, we suspect that physiological mechanisms are the basis for the observed differences in lifespan.

A critical look at proximate causes of social insect senescence: damage accumulation or hyperfunction?

Social insects have received attention for their extreme lifespan variation and reversal of the fecundity/longevity trade-off. However, proximate causes of senescence in general are disputed, and social insects often fail to meet the predictions of prevailing models. We present evidence for and against the long-held free radical theory of aging in social insects, and consider the application of the competing hyperfunction theory. Current results present problems for both theories, and a more complex picture of the biological processes involved emerges. The eusocial life style might allow colonies to allocate damage in ways that create seemingly senescence-free life histories. Only experimental approaches characterizing multiple senescence factors simultaneously will shed light on how social insects defy the conventions of senescence.

Early gut colonizers shape parasite susceptibility and microbiota composition in honey bee workers

Microbial symbionts living within animal guts are largely composed of resident bacterial species, forming communities that often provide benefits to the host. Gut microbiomes of adult honey bees (Apis mellifera) include core residents such as the betaproteobacterium Snodgrassella alvi, alongside transient parasites such as the protozoan Lotmaria passim To test how these species affect microbiome composition and host physiology, we administered S alvi and/or L passim inocula to newly emerged worker bees from four genetic backgrounds (GH) and reared them in normal (within hives) or stressed (protein-deficient, asocial) conditions. Microbiota acquired by normal bees were abundant but quantitatively differed across treatments, indicating treatment-associated dysbiosis. Pretreatment with S. alvi made normal bees more susceptible to L. passim and altered developmental and detoxification gene expression. Stressed bees were more susceptible to L. passim and were depauperate in core microbiota, yet supplementation with S. alvi did not alter this susceptibility. Microbiomes were generally more variable by GH in stressed bees, which also showed opposing and comparatively reduced modulation of gene expression responses to treatments compared with normal bees. These data provide experimental support for a link between altered gut microbiota and increased parasite and pathogen prevalence, as observed from honey bee colony collapse disorder.

Linking Measures of Colony and Individual Honey Bee Health to Survival among Apiaries Exposed to Varying Agricultural Land Use

We previously characterized and quantified the influence of land use on survival and productivity of colonies positioned in six apiaries and found that colonies in apiaries surrounded by more land in uncultivated forage experienced greater annual survival, and generally more honey production. Here, detailed metrics of honey bee health were assessed over three years in colonies positioned in the same six apiaries. The colonies were located in North Dakota during the summer months and were transported to California for almond pollination every winter. Our aim was to identify relationships among measures of colony and individual bee health that impacted and predicted overwintering survival of colonies. We tested the hypothesis that colonies in apiaries surrounded by more favorable land use conditions would experience improved health. We modeled colony and individual bee health indices at a critical time point (autumn, prior to overwintering) and related them to eventual spring survival for California almond pollination. Colony measures that predicted overwintering apiary survival included the amount of pollen collected, brood production, and Varroa destructor mite levels. At the individual bee level, expression of vitellogenin, defensin1, and lysozyme2 were important markers of overwinter survival. This study is a novel first step toward identifying pertinent physiological responses in honey bees that result from their positioning near varying landscape features in intensive agricultural environments.

Elephants born in the high stress season have faster reproductive ageing

Senescent declines in reproduction and survival are found across the tree of life, but little is known of the factors causing individual variation in reproductive ageing rates. One contributor may be variation in early developmental conditions, but only a few studies quantify the effects of early environment on reproductive ageing and none concern comparably long-lived species to humans. We determine the effects of ‘stressful’ birth conditions on lifetime reproduction in a large semi-captive population of Asian elephants (Elephas maximus). We categorise birth month into stressful vs. not-stressful periods based on longitudinal measures of glucocorticoid metabolites in reproductive-aged females, which peak during heavy workload and the start of the monsoon in June-August. Females born in these months exhibit faster reproductive senescence in adulthood and have significantly reduced lifetime reproductive success than their counterparts born at other times of year. Improving developmental conditions could therefore delay reproductive ageing in species as long-lived as humans.

Mating Reverses Actuarial Aging in Female Queensland Fruit Flies

Animals that have a long pre-reproductive adult stage often employ mechanisms that minimize aging over this period in order to preserve reproductive lifespan. In a remarkable exception, one tephritid fruit fly exhibits substantial pre-reproductive aging but then mitigates this aging during a diet-dependent transition to the reproductive stage, after which life expectancy matches that of newly emerged flies. Here, we ascertain the role of nutrients, sexual maturation and mating in mitigation of previous aging in female Queensland fruit flies. Flies were provided one of three diets: ‘sugar’, ‘essential’, or ‘yeast-sugar’. Essential diet contained sugar and micronutrients found in yeast but lacked maturation-enabling protein. At days 20 and 30, a subset of flies on the sugar diet were switched to essential or yeast-sugar diet, and some yeast-sugar fed flies were mated 10 days later. Complete mitigation of actuarial aging was only observed in flies that were switched to a yeast-sugar diet and mated, indicating that mating is key. Identifying the physiological processes associated with mating promise novel insights into repair mechanisms for aging.

Behavioral Reversion and Dark-Light Choice Behavior in Workers of the Red Wood Ant Formica polyctena

Social insect workers usually start adult life from intranidal tasks and then switch to extranidal activities, but this process may be reversed: foragers may switch again to intranidal brood care. The transition forager - reverted nurse is known as the behavioral reversion. Ant foragers are known to avoid illuminated zones less strongly than intranidal workers, but illumination responses of reverted nurses were so far never investigated. We compared dark-light choice behavior of three classes of workers of the red wood ant Formica polyctena: nurses, foragers and reverted nurses. Sets of ten ants belonging to the same class were tested in "double nests" made of two interconnected test tubes, one kept in darkness and the other exposed to light. The number of ants present in the illuminated zone of each nest (ni) was recorded on 10 sample points at 30 min intervals. The values of ni were lower in nurses than in foragers and reverted nurses and decreased as a function of time in all three groups. Nurses differed from foragers with respect to the dynamics of dark-light choice behavior, but reverted nurses did not differ in that respect either from nurses, or from foragers. Reverted nurses and foragers did not differ significantly from each other with respect to the overall level of avoidance of illuminated zone, nor with respect to the dynamics of dark-light choice behavior. This implies that behavioral reversion is not accompanied by the return of illumination responses of workers of F. polyctena to the state characteristic for nurses.