Transferrin-mediated iron sequestration suggests a novel therapeutic strategy for controlling Nosema disease in the honey bee, Apis mellifera.

Nosemosis C, a Nosema disease caused by microsporidia parasite Nosema ceranae, is a significant disease burden of the European honey bee Apis mellifera which is one of the most economically important insect pollinators. Nevertheless, there is no effective treatment currently available for Nosema disease and the disease mechanisms underlying the pathological effects of N. ceranae infection in honey bees are poorly understood. Iron is an essential nutrient for growth and survival of hosts and pathogens alike. The iron tug-of-war between host and pathogen is a central battlefield at the host-pathogen interface which determines the outcome of an infection, however, has not been explored in honey bees. To fill the gap, we conducted a study to investigate the impact of N. ceranae infection on iron homeostasis in honey bees. The expression of transferrin, an iron binding and transporting protein that is one of the key players of iron homeostasis, in response to N. ceranae infection was analysed. Furthermore, the functional roles of transferrin in iron homeostasis and honey bee host immunity were characterized using an RNA interference (RNAi)-based method. The results showed that N. ceranae infection causes iron deficiency and upregulation of the A. mellifera transferrin (AmTsf) mRNA in honey bees, implying that higher expression of AmTsf allows N. ceranae to scavenge more iron from the host for its proliferation and survival. The suppressed expression levels of AmTsf via RNAi could lead to reduced N. ceranae transcription activity, alleviated iron loss, enhanced immunity, and improved survival of the infected bees. The intriguing multifunctionality of transferrin illustrated in this study is a significant contribution to the existing body of literature concerning iron homeostasis in insects. The uncovered functional role of transferrin on iron homeostasis, pathogen growth and honey bee's ability to mount immune responses may hold the key for the development of novel strategies to treat or prevent diseases in honey bees.

Impacts of seasonality and parasitism on honey bee population dynamics.

The honeybee plays an extremely important role in ecosystem stability and diversity and in the production of bee pollinated crops. Honey bees and other pollinators are under threat from the combined effects of nutritional stress, parasitism, pesticides, and climate change that impact the timing, duration, and variability of seasonal events. To understand how parasitism and seasonality influence honey bee colonies separately and interactively, we developed a non-autonomous nonlinear honeybee-parasite interaction differential equation model that incorporates seasonality into the egg-laying rate of the queen. Our theoretical results show that parasitism negatively impacts the honey bee population either by decreasing colony size or destabilizing population dynamics through supercritical or subcritical Hopf-bifurcations depending on conditions. Our bifurcation analysis and simulations suggest that seasonality alone may have positive or negative impacts on the survival of honey bee colonies. More specifically, our study indicates that (1) the timing of the maximum egg-laying rate seems to determine when seasonality has positive or negative impacts; and (2) when the period of seasonality is large it can lead to the colony collapsing. Our study further suggests that the synergistic influences of parasitism and seasonality can lead to complicated dynamics that may positively and negatively impact the honey bee colony's survival. Our work partially uncovers the intrinsic effects of climate change and parasites, which potentially provide essential insights into how best to maintain or improve a honey bee colony's health.

Inferring pesticide toxicity to honey bees from a field-based feeding study using a colony model and Bayesian inference.

Honey bees are crucial pollinators for agricultural crops but are threatened by a multitude of stressors including exposure to pesticides. Linking our understanding of how pesticides affect individual bees to colony-level responses is challenging because colonies show emergent properties based on complex internal processes and interactions among individual bees. Agent-based models that simulate honey bee colony dynamics may be a tool for scaling between individual and colony effects of a pesticide. The U.S. Environmental Protection Agency (USEPA) and U.S. Department of Agriculture (USDA) are developing the VarroaPop + Pesticide model, which simulates the dynamics of honey bee colonies and how they respond to multiple stressors, including weather, Varroa mites, and pesticides. To evaluate this model, we used Approximate Bayesian Computation to fit field data from an empirical study where honey bee colonies were fed the insecticide clothianidin. This allowed us to reproduce colony feeding study data by simulating colony demography and mortality from ingestion of contaminated food. We found that VarroaPop + Pesticide was able to fit general trends in colony population size and structure and reproduce colony declines from increasing clothianidin exposure. The model underestimated adverse effects at low exposure (36 µg/kg), however, and overestimated recovery at the highest exposure level (140 µg/kg), for the adult and pupa endpoints, suggesting that mechanisms besides oral toxicity-induced mortality may have played a role in colony declines. The VarroaPop + Pesticide model estimates an adult oral LD50 of 18.9 ng/bee (95% CI 10.1-32.6) based on the simulated feeding study data, which falls just above the 95% confidence intervals of values observed in laboratory toxicology studies on individual bees. Overall, our results demonstrate a novel method for analyzing colony-level data on pesticide effects on bees and making inferences on pesticide toxicity to individual bees.

The active ingredients of a mitotoxic fungicide negatively affect pollen consumption and worker survival in laboratory-reared honey bees (Apis mellifera).

Recent observations of many sublethal effects of pesticides on pollinators have raised questions about whether standard short-term laboratory tests of pesticide effects on survival are sufficient for pollinator protection. The fungicide Pristine® and its active ingredients (25.2% boscalid, 12.8% pyraclostrobin) have been reported to have low acute toxicity to caged honey bee workers, but many sublethal effects at field-relevant doses have been reported and Pristine® was recently found to increase worker pollen consumption, reduce worker longevity and colony populations at field relevant concentrations (Fisher et al. 2021). To directly compare these whole-colony field results to more standard laboratory toxicology tests, the effects of Pristine®, at a range of field-relevant concentrations, were assessed on the survival and pollen consumption of honey bee workers 0-14 days of age. Also, to separate the effects of the inert and two active ingredients, bees were fed pollen containing boscalid, pyraclostrobin, or pyraclostrobin plus boscalid, at concentrations matching those in the Pristine® treatments. Pyraclostrobin significantly reduced pollen consumption across the duration of the experiment, and dose-dependently reduced pollen consumption on days 12-14. Pristine® and boscalid significantly reduced pollen feeding rate on days 12-14. Boscalid reduced survival in a dose-dependent manner. Consumption of Pristine® or pyraclostrobin plus boscalid did not affect survival, providing evidence against strong negative effects of the inert ingredients in Pristine® and against negative synergistic effects of boscalid and pyraclostrobin. The stronger toxic effects of Pristine® observed in field colonies compared to this laboratory test, and the opposite responses of pollen consumption in the laboratory and field to Pristine®, show that standard laboratory toxicology tests can fail to predict responses of pollinators to pesticides and to provide protection.

Field cross-fostering and in vitro rearing demonstrate negative effects of both larval and adult exposure to a widely used fungicide in honey bees (Apis mellifera).

Pollinators and other insects are experiencing an ongoing worldwide decline. While various environmental stressors have been implicated, including pesticide exposure, the causes of these declines are complex and highly debated. Fungicides may constitute a particularly prevalent threat to pollinator health due to their application on many crops during bloom, and because pollinators such as bees may consume fungicide-tainted pollen or nectar. In a previous study, consumption of pollen containing the fungicide Pristine® at field-relevant concentrations by honey bee colonies increased pollen foraging, caused earlier foraging, lowered worker survival, and reduced colony population size. Because most pollen is consumed by young adults, we hypothesized that Pristine® (25.2% boscalid, 12.8% pyraclostrobin) in pollen exerts its negative effects on honey bee colonies primarily on the adult stage. To rigorously test this hypothesis, we used a cross-fostering experimental design, with bees reared in colonies provided Pristine® incorporated into pollen patties at a supra-field concentration (230 mg/kg), only in the larvae, only in the adult, or both stages. In contrast to our predictions, exposure to Pristine® in either the larval or adult stage reduced survival relative to control bees not exposed to Pristine®, and exposure to the fungicide at both larval and adult stages further reduced survival. Adult exposure caused precocious foraging, while larval exposure increased the tendency to forage for pollen. These results demonstrate that pollen containing Pristine® can induce significant negative effects on both larvae and adults in a hive, though the magnitude of such effects may be smaller at field-realistic doses. To further test the potential negative effects of direct consumption of Pristine® on larvae, we reared them in vitro on food containing Pristine® at a range of concentrations. Consumption of Pristine® reduced survival rates of larvae at all concentrations tested. Larval and adult weights were only reduced at a supra-field concentration. We conclude that consumption of pollen containing Pristine® by field honey bee colonies likely exerts impacts on colony population size and foraging behavior by affecting both larvae and adults.

Can supplementary pollen feeding reduce varroa mite and virus levels and improve honey bee colony survival?

Varroa destructor is an ectoparasitic mite of immature and adult honey bees that can transmit several single-stranded RNA viruses to its host. Varroa reproduce in brood cells, and mite populations increase as colonies produce brood in spring and summer. Mite numbers also can sharply rise, particularly in the fall, by the migration of varroa into hives on foragers. Colonies with high levels of varroa and viruses often die over the winter. Feeding colonies pollen might keep virus levels low and improve survival because of the positive effects of pollen on immunity and colony growth. We compared varroa and virus levels and overwinter survival in colonies with (fed) and without (unfed) supplemental pollen. We also measured the frequency of capturing foragers with mites (FWM) at colony entrances to determine its relationship to varroa and virus levels. Colonies fed supplemental pollen were larger than unfed colonies and survived longer. Varroa populations and levels of Deformed wing virus (DWV) rose throughout the season, and were similar between fed and unfed colonies. The growth of varroa populations was correlated with FWM in fed and unfed colonies, and significantly affected DWV levels. Increasing frequencies of FWM and the effects on varroa populations might reduce the positive influence of supplemental pollen on immune function. However, pollen feeding can stimulate colony growth and this can improve colony survival.

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 honey bee biology such as caste, immunity, lifespan, growth and behavioral development. Deformed wing virus (DWV) is a major pathogenic factor which threatens honey bee populations, and its replication is regulated by the nutrition status and immune response of honey bees. The alimentary canal of the honey bee is home to a diverse microbial community that provides essential nutrients and serves to bolster immune responses. However, to what extent gut bacteria affect honey bee 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 or (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 jellyprotein 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 honey bees at 7 days post-antibiotic treatment. Additionally, honey bee head mass and survival rate were measured. We observed that antibiotics decreased the expression of tor and rel, and increased DWV titer and its replication activity. Expression of ilp1, mrjp1-5 and vg, and honey bee head mass were also reduced compared with bees on a pollen diet. Antibiotics also caused a significant drop in survivorship, which could be rescued by addition of pollen to the diet. Of importance, pollen could partially rescue the loss of vg and mrjp2 while also increasing the head mass of antibiotic-treated bees. Our results illuminate the roles of bacteria in honey bee nutrition, metabolism and immunity, which confer the ability to inhibit virus replication, extend honey bee lifespan and improve overall health.

Transcriptional response of honey bee (Apis mellifera) to differential nutritional status and Nosema infection.

BACKGROUND: Bees are confronting several environmental challenges, including the intermingled effects of malnutrition and disease. Intuitively, pollen is the healthiest nutritional choice, however, commercial substitutes, such as Bee-Pro and MegaBee, are widely used. Herein we examined how feeding natural and artificial diets shapes transcription in the abdomen of the honey bee, and how transcription shifts in combination with Nosema parasitism. RESULTS: Gene ontology enrichment revealed that, compared with poor diet (carbohydrates [C]), bees fed pollen (P > C), Bee-Pro (B > C), and MegaBee (M > C) showed a broad upregulation of metabolic processes, especially lipids; however, pollen feeding promoted more functions, and superior proteolysis. The superiority of the pollen diet was also evident through the remarkable overexpression of vitellogenin in bees fed pollen instead of MegaBee or Bee-Pro. Upregulation of bioprocesses under carbohydrates feeding compared to pollen (C > P) provided a clear poor nutritional status, uncovering stark expression changes that were slight or absent relatively to Bee-Pro (C > B) or MegaBee (C > M). Poor diet feeding (C > P) induced starvation response genes and hippo signaling pathway, while it repressed growth through different mechanisms. Carbohydrate feeding (C > P) also elicited 'adult behavior', and developmental processes suggesting transition to foraging. Finally, it altered the 'circadian rhythm', reflecting the role of this mechanism in the adaptation to nutritional stress in mammals. Nosema-infected bees fed pollen compared to carbohydrates (PN > CN) upheld certain bioprocesses of uninfected bees (P > C). Poor nutritional status was more apparent against pollen (CN > PN) than Bee-Pro (CN > BN) or MegaBee (CN > MN). Nosema accentuated the effects of malnutrition since more starvation-response genes and stress response mechanisms were upregulated in CN > PN compared to C > P. The bioprocess 'Macromolecular complex assembly' was also enriched in CN > PN, and involved genes associated with human HIV and/or influenza, thus providing potential candidates for bee-Nosema interactions. Finally, the enzyme Duox emerged as essential for guts defense in bees, similarly to Drosophila. CONCLUSIONS: These results provide evidence of the superior nutritional status of bees fed pollen instead of artificial substitutes in terms of overall health, even in the presence of a pathogen.

Nosema ceranae parasitism impacts olfactory learning and memory and neurochemistry in honey bees (Apis mellifera).

Nosema sp. is an internal parasite of the honey bee, Apis mellifera, and one of the leading contributors to colony losses worldwide. This parasite is found in the honey bee midgut and has profound consequences for the host's physiology. Nosema sp. impairs foraging performance in honey bees, yet, it is unclear whether this parasite affects the bee's neurobiology. In this study, we examined whether Nosema sp. affects odor learning and memory and whether the brains of parasitized bees show differences in amino acids and biogenic amines. We took newly emerged bees and fed them with Nosema ceranae At approximate nurse and forager ages, we employed an odor-associative conditioning assay using the proboscis extension reflex and two bioanalytical techniques to measure changes in brain chemistry. We found that nurse-aged bees infected with N. ceranae significantly outperformed controls in odor learning and memory, suggestive of precocious foraging, but by forager age, infected bees showed deficits in learning and memory. We also detected significant differences in amino acid concentrations, some of which were age specific, as well as altered serotonin, octopamine, dopamine and l-dopa concentrations in the brains of parasitized bees. These findings suggest that N. ceranae infection affects honey bee neurobiology and may compromise behavioral tasks. These results yield new insight into the host-parasite dynamic of honey bees and N. ceranae, as well as the neurochemistry of odor learning and memory under normal and parasitic conditions.

Smoke Conditions Affect the Release of the Venom Droplet Accompanying Sting Extension in Honey Bees (Hymenoptera: Apidae).

Honey bees (Apis mellifera) (Hymenoptera: Apidae) are social insects that have evolved a coordinated defensive response to ensure colony survival. Their nests may contain valuable resources such as pollen and nectar that are attractive to a range of insect and mammalian intruders and need protecting. With sufficient provocation, honey bees will mobilize and sting intruders, who are likely to incur additional stings. To inspect and manage their colonies, beekeepers apply smoke to decrease the likelihood of being stung. The use of smoke is a ubiquitous beekeeping practice, but the reasons behind its efficacy remain unknown. In this study, we examined the effects of smoke on honey bee defensive behavior by assessing individual sting extension responses under smoke conditions. We applied a brief voltage to the bee, ranging from a mild to a strong perturbation, and assessed four components of the sting extension reflex using two types of smoke. We found that smoke did not influence the probability of sting extension, but it did affect whether a venom droplet was released with the stinger. The venom droplet was more likely to be released at higher voltage levels, but this effect was significantly reduced under smoke conditions. Based on these results, we propose that the venom droplet coincides with greater agitation in individual bees; and smoke reduces the probability of its release. We speculate that the venom droplet serves to amplify the sting alarm pheromone, and smoke, in its ability to reduce droplet formation, may indicate that less alarm pheromone is released.

Sensitivity analyses for simulating pesticide impacts on honey bee colonies.

We employ Monte Carlo simulation and sensitivity analysis techniques to describe the population dynamics of pesticide exposure to a honey bee colony using the VarroaPop+Pesticide model. Simulations are performed of hive population trajectories with and without pesticide exposure to determine the effects of weather, queen strength, foraging activity, colony resources, and Varroa populations on colony growth and survival. The daily resolution of the model allows us to conditionally identify sensitivity metrics. Simulations indicate queen strength and forager lifespan are consistent, critical inputs for colony dynamics in both the control and exposed conditions. Adult contact toxicity, application rate and nectar load become critical parameters for colony dynamics within exposed simulations. Daily sensitivity analysis also reveals that the relative importance of these parameters fluctuates throughout the simulation period according to the status of other inputs.

Israeli acute paralysis virus: epidemiology, pathogenesis and implications for honey bee health.

Israeli acute paralysis virus (IAPV) is a widespread RNA virus of honey bees that has been linked with colony losses. Here we describe the transmission, prevalence, and genetic traits of this virus, along with host transcriptional responses to infections. Further, we present RNAi-based strategies for limiting an important mechanism used by IAPV to subvert host defenses. Our study shows that IAPV is established as a persistent infection in honey bee populations, likely enabled by both horizontal and vertical transmission pathways. The phenotypic differences in pathology among different strains of IAPV found globally may be due to high levels of standing genetic variation. Microarray profiles of host responses to IAPV infection revealed that mitochondrial function is the most significantly affected biological process, suggesting that viral infection causes significant disturbance in energy-related host processes. The expression of genes involved in immune pathways in adult bees indicates that IAPV infection triggers active immune responses. The evidence that silencing an IAPV-encoded putative suppressor of RNAi reduces IAPV replication suggests a functional assignment for a particular genomic region of IAPV and closely related viruses from the Family Dicistroviridae, and indicates a novel therapeutic strategy for limiting multiple honey bee viruses simultaneously and reducing colony losses due to viral diseases. We believe that the knowledge and insights gained from this study will provide a new platform for continuing studies of the IAPV-host interactions and have positive implications for disease management that will lead to mitigation of escalating honey bee colony losses worldwide.

Population growth of Varroa destructor (Acari: Varroidae) in honey bee colonies is affected by the number of foragers with mites.

Varroa mites are a serious pest of honey bees and the leading cause of colony losses. Varroa have relatively low reproductive rates, so populations should not increase rapidly, but often they do. Other factors might contribute to the growth of varroa populations including mite migration into colonies on foragers from other hives. We measured the proportion of foragers carrying mites on their bodies while entering and leaving hives, and determined its relationship to the growth of varroa populations in those hives at two apiary sites. We also compared the estimates of mite population growth with predictions from a varroa population dynamics model that generates estimates of mite population growth based on mite reproduction. Samples of capped brood and adult bees indicated that the proportion of brood cells infested with mites and adult bees with phoretic mites was low through the summer but increased sharply in the fall especially at site 1. The frequency of capturing foragers with mites on their bodies while entering or leaving hives also increased in the fall. The growth of varroa populations at both sites was not significantly related to our colony estimates of successful mite reproduction, but instead to the total number of foragers with mites (entering and leaving the colony). There were more foragers with mites at site 1 than site 2, and mite populations at site 1 were larger especially in the fall. The model accurately estimated phoretic mite populations and infested brood cells until November when predictions were much lower than those measured in colonies. The rapid growth of mite populations particularly in the fall being a product of mite migration rather than mite reproduction only is discussed.

Mixed infections reveal virulence differences between host-specific bee pathogens.

Dynamics of host-pathogen interactions are complex, often influencing the ecology, evolution and behavior of both the host and pathogen. In the natural world, infections with multiple pathogens are common, yet due to their complexity, interactions can be difficult to predict and study. Mathematical models help facilitate our understanding of these evolutionary processes, but empirical data are needed to test model assumptions and predictions. We used two common theoretical models regarding mixed infections (superinfection and co-infection) to determine which model assumptions best described a group of fungal pathogens closely associated with bees. We tested three fungal species, Ascosphaera apis, Ascosphaera aggregata and Ascosphaera larvis, in two bee hosts (Apis mellifera and Megachile rotundata). Bee survival was not significantly different in mixed infections vs. solo infections with the most virulent pathogen for either host, but fungal growth within the host was significantly altered by mixed infections. In the host A. mellifera, only the most virulent pathogen was present in the host post-infection (indicating superinfective properties). In M. rotundata, the most virulent pathogen co-existed with the lesser-virulent one (indicating co-infective properties). We demonstrated that the competitive outcomes of mixed infections were host-specific, indicating strong host specificity among these fungal bee pathogens.

New meta-analysis tools reveal common transcriptional regulatory basis for multiple determinants of behavior.

A fundamental problem in meta-analysis is how to systematically combine information from multiple statistical tests to rigorously evaluate a single overarching hypothesis. This problem occurs in systems biology when attempting to map genomic attributes to complex phenotypes such as behavior. Behavior and other complex phenotypes are influenced by intrinsic and environmental determinants that act on the transcriptome, but little is known about how these determinants interact at the molecular level. We developed an informatic technique that identifies statistically significant meta-associations between gene expression patterns and transcription factor combinations. Deploying this technique for brain transcriptome profiles from ca. 400 individual bees, we show that diverse determinants of behavior rely on shared combinations of transcription factors. These relationships were revealed only when we considered complex and variable regulatory rules, suggesting that these shared transcription factors are used in distinct ways by different determinants. This regulatory code would have been missed by traditional gene coexpression or cis-regulatory analytic methods. We expect that our meta-analysis tools will be useful for a broad array of problems in systems biology and other fields.

Effects of Oral Exposure to Fungicides on Honey Bee Nutrition and Virus Levels.

Sublethal exposure to fungicides can affect honey bees (Apis mellifera L.) in ways that resemble malnutrition. These include reduced brood rearing, queen loss, and increased pathogen levels. We examined the effects of oral exposure to the fungicides boscalid and pyraclostrobin on factors affecting colony nutrition and immune function including pollen consumption, protein digestion, hemolymph protein titers, and changes in virus levels. Because the fungicides are respiratory inhibitors, we also measured ATP concentrations in flight muscle. The effects were evaluated in 3- and 7-d-old worker bees at high fungicide concentrations in cage studies, and at field-relevant concentrations in colony studies. Though fungicide levels differed greatly between the cage and colony studies, similar effects were observed. Hemolymph protein concentrations were comparable between bees feeding on pollen with and without added fungicides. However, in both cage and colony studies, bees consumed less pollen containing fungicides and digested less of the protein. Bees fed fungicide-treated pollen also had lower ATP concentrations and higher virus titers. The combination of effects we detected could produce symptoms that are similar to those from poor nutrition and weaken colonies making them more vulnerable to loss from additional stressors such as parasites and pathogens.

Population growth of Varroa destructor (Acari: Varroidae) in commercial honey bee colonies treated with beta plant acids.

Varroa (Varroa destuctor Anderson and Trueman) populations in honey bee (Apis mellifera L.) colonies might be kept at low levels by well-timed miticide applications. HopGuard(®) (HG) that contains beta plant acids as the active ingredient was used to reduce mite populations. Schedules for applications of the miticide that could maintain low mite levels were tested in hives started from either package bees or splits of larger colonies. The schedules were developed based on defined parameters for efficacy of the miticide and predictions of varroa population growth generated from a mathematical model of honey bee colony-varroa population dynamics. Colonies started from package bees and treated with HG in the package only or with subsequent HG treatments in the summer had 1.2-2.1 mites per 100 bees in August. Untreated controls averaged significantly more mites than treated colonies (3.3 mites per 100 bees). By October, mite populations ranged from 6.3 to 15.0 mites per 100 bees with the lowest mite numbers in colonies treated with HG in August. HG applications in colonies started from splits in April reduced mite populations to 0.12 mites per 100 bees. In September, the treated colonies had significantly fewer mites than the untreated controls. Subsequent HG applications in September that lasted for 3 weeks reduced mite populations to levels in November that were significantly lower than in colonies that were untreated or had an HG treatment that lasted for 1 week. The model accurately predicted colony population growth and varroa levels until the fall when varroa populations measured in colonies established from package bees or splits were much greater than predicted. Possible explanations for the differences between actual and predicted mite populations are discussed.

Warmer autumns and winters could reduce honey bee overwintering survival with potential risks for pollination services.

Honey bees and other pollinators are critical for food production and nutritional security but face multiple survival challenges. The effect of climate change on honey bee colony losses is only recently being explored. While correlations between higher winter temperatures and greater colony losses have been noted, the impacts of warmer autumn and winter temperatures on colony population dynamics and age structure as an underlying cause of reduced colony survival have not been examined. Focusing on the Pacific Northwest US, our objectives were to (a) quantify the effect of warmer autumns and winters on honey bee foraging activity, the age structure of the overwintering cluster, and spring colony losses, and (b) evaluate indoor cold storage as a management strategy to mitigate the negative impacts of climate change. We perform simulations using the VARROAPOP population dynamics model driven by future climate projections to address these objectives. Results indicate that expanding geographic areas will have warmer autumns and winters extending honey bee flight times. Our simulations support the hypothesis that late-season flight alters the overwintering colony age structure, skews the population towards older bees, and leads to greater risks of colony failure in the spring. Management intervention by moving colonies to cold storage facilities for overwintering has the potential to reduce honey bee colony losses. However, critical gaps remain in how to optimize winter management strategies to improve the survival of overwintering colonies in different locations and conditions. It is imperative that we bridge the gaps to sustain honey bees and the beekeeping industry and ensure food and nutritional security.

The survival and growth of honey bee (Hymenoptera: Apidae) colonies overwintered in cold storage: the effects of time and colony location.

For over a decade, high percentages of honey bee colonies have been perishing during the winter creating economic hardship to beekeepers and growers of early-season crops requiring pollination. A way to reduce colony losses might be moving hives into cold storage facilities for the winter. We explored factors that could affect the size and survival of colonies overwintered in cold storage and then used for almond pollination. The factors were when hives were put into cold storage and their location prior to overwintering. We found that colonies summered in North Dakota, USA and moved to cold storage in October were larger after cold storage and almond pollination than those moved in November. Colony location prior to overwintering also affected size and survival. Colonies summered in southern Texas, USA and moved to cold storage in November were smaller after cold storage and almond pollination than those from North Dakota. The colonies also were smaller than those overwintered in Texas apiaries. Fat body metrics of bees entering cold storage differed between summer locations. North Dakota bees had higher lipid and lower protein concentrations than Texas bees. While in cold storage, fat bodies gained weight, protein concentrations increased, and lipids decreased. The decrease in lipid concentrations was correlated with the amount of brood reared while colonies were in cold storage. Our study indicates that in northern latitudes, overwintering survival might be affected by when colonies are put into cold storage and that colonies summered in southern latitudes should be overwintered there.

Mediating a host cell signaling pathway linked to overwinter mortality offers a promising therapeutic approach for improving bee health.

INTRODUCTION: Honey bees provides valuable pollination services for world food crops and wild flowering plants which are habitats of many animal species and remove carbon dioxide from the atmosphere, a powerful tool in the fight against climate change. Nevertheless, the honey bee population has been declining and the majority of colony losses occur during the winter. OBJECTIVES: The goal of this study was to understand the mechanisms underlying overwinter colony losses and develop novel therapeutic strategies for improving bee health. METHODS: First, pathogen prevalence in overwintering bees were screened between 2015 and 2018. Second, RNA sequencing (RNA-Seq) for transcriptional profiling of overwintering honey bees was conducted and qRT-PCR was performed to confirm the results of the differential expression of selected genes. Lastly, laboratory bioassays were conducted to measure the effects of cold challenges on bee survivorship and stress responses and to assess the effect of a novel medication for alleviating cold stress in honey bees. RESULTS: We identified that sirtuin signaling pathway is the most significantly enriched pathway among the down-regulated differentially expressed genes (DEGs) in overwintering diseased bees. Moreover, we showed that the expression of SIRT1 gene, a major sirtuin that regulates energy and immune metabolism, was significantly downregulated in bees merely exposed to cold challenges, linking cold stress with altered gene expression of SIRT1. Furthermore, we demonstrated that activation of SIRT1 gene expression by SRT1720, an activator of SIRT1 expression, could improve the physiology and extend the lifespan of cold-stressed bees. CONCLUSION: Our study suggests that increased energy consumption of overwintering bees for maintaining hive temperature reduces the allocation of energy toward immune functions, thus making the overwintering bees more susceptible to disease infections and leading to high winter colony losses. The novel information gained from this study provides a promising avenue for the development of therapeutic strategies for mitigating colony losses, both overwinter and annually.