Endothermic heat production in honeybee winter clusters

Social life results in social stress protection: a novel concept to explain individual life-history patterns in social insects

Resistance to and avoidance of stress slow aging and confer increased longevity in numerous organisms. Honey bees and other superorganismal social insects have two main advantages over solitary species to avoid or resist stress: individuals can directly help each other by resource or information transfer, and they can cooperatively control their environment. These benefits have been recognised in the context of pathogen and parasite stress as the concept of social immunity, which has been extensively studied. However, we argue that social immunity is only a special case of a general concept that we define here as social stress protection to include group-level defences against all biotic and abiotic stressors. We reason that social stress protection may have allowed the evolution of reduced individual-level defences and individual life-history optimization, including the exceptional aging plasticity of many social insects. We describe major categories of stress and how a colonial lifestyle may protect social insects, particularly against temporary peaks of extreme stress. We use the honey bee (Apis mellifera L.) to illustrate how patterns of life expectancy may be explained by social stress protection and how modern beekeeping practices can disrupt social stress protection. We conclude that the broad concept of social stress protection requires rigorous empirical testing because it may have implications for our general understanding of social evolution and specifically for improving honey bee health.

Are man-made hives valid thermal surrogates for natural honey bee nests (Apismellifera)?

Honey bees preferentially occupy thick walled tall narrow tree cavities and attach their combs directly to the nest wall, leaving periodic gaps. However, academic research and beekeeping are conducted in squat, thin walled man made hives, with a continuous gap between the combs and the walls and roof. Utilising a computational fluid dynamics (CFD) model of thermoregulating bees in complete nests in trees and thin walled man made hives, with the average size of tree comb gaps determined from honey bee occupied synthetic tree nests, this research compared the metabolic energy impacts of comb gaps and vertical movement of the thermoregulated brood area. This shows their heat transfer regimes are disparate, including: bee space above combs increases heat loss by up to ∼70%; hives, compared to tree nests, require at least 150% the density of honey bees to arrest convection across the brood area. Tree cavities have a larger vertical freedom, a greater thermal resistance and can make dense clustering redundant. With the thermal environment being critical to honey bees, the magnitude and scope of these differences suggest that some hive based behavioural research needs extra validation to be considered non-anthropogenic, and some bee keeping practices are sub-optimal.

Giant honeybees (Apis dorsata) trade off defensiveness against periodic mass flight activity

The giant honeybee Apis dorsata (Fabricius, 1793) is an evolutionarily ancient species that builds its nests in the open. The nest consists of a single honeycomb covered with the bee curtain which are several layers of worker bees that remain almost motionless with their heads up and abdomens down on the nest surface, except for the mouth area, the hub between inner- and outer-nest activities. A colony may change this semi-quiescence several times a day, depending on its reproductive state and ambient temperature, to enter the state of mass flight activity (MFA), in which nest organisation is restructured and defense ability is likely to be suppressed (predicted by the mass-flight-suspend-defensiveness hypothesis). For this study, three episode of MFA (mfa1-3) of a selected experimental nest were analysed in a case study with sequences of >60 000 images at 50 Hz, each comprise a short pre-MFA session, the MFA and the post-MFA phase of further 10 min. To test colony defensiveness under normative conditions, a dummy wasp was cyclically presented with a standardised motion programme (Pd) with intervening sessions without such a presentation (nPd). Motion activity at five selected surveillance zones (sz1-5) on the nest were analysed. In contrast to mfa1,2, in mfa3 the experimental regime started with the cyclic presentation of the dummy wasp only after the MFA had subsided. As a result, the MFA intensity in mfa3 was significantly lower than in mfa1-2, suggesting that a colony is able to perceive external threats during the MFA. Characteristic ripples appear in the motion profiles, which can be interpreted as a start signal for the transition to MFA. Because they are strongest in the mouth zone and shift to higher frequencies on their way to the nest periphery, it can be concluded that MFA starts earlier in the mouth zone than in the peripheral zones, also suggesting that the mouth zone is a control centre for the scheduling of MFA. In Pd phases of pre- and postMFA, the histogram-based motion spectra are biphasic, suggesting two cohorts in the process, one remaining at quiescence and the other involved in shimmering. Under MFA, nPd and Pd spectra were typically Gaussian, suggesting that the nest mates with a uniform workload shifted to higher motion activity. At the end of the MFA, the spectra shift back to the lower motion activities and the Pd spectra form a biphasic again. This happens a few minutes earlier in the peripheral zones than in the mouth zone. Using time profiles of the skewness of the Pd motion spectra, the mass-flight-suspend-defensiveness hypothesis is confirmed, whereby the inhibition of defense ability was found to increase progressively during the MFA. These sawtooth-like time profiles of skewness during MFA show that defense capability is recovered again quite quickly at the end of MFA. Finally, with the help of the Pd motion spectra, clear indications can be obtained that the giant honeybees engage in a decision in the sense of a tradeoff between MFA and collective defensiveness, especially in the regions in the periphery to the mouth zone.

Stress-induced loss of social resilience in honeybee colonies and its implications on fitness

Stressors may lead to a shift in the timing of life-history events of species, causing a mismatch with optimal environmental conditions, potentially reducing fitness. In honeybees, the timing of brood rearing and nest emergence in late winter/early spring is critical as colonies need to grow fast after winter to prepare for reproduction. However, the effects of stress on these life-history events in late winter/early spring and the possible consequences are not well understood. Therefore, we tested whether (i) honeybee colonies shift timing of brood rearing and nest emergence as response to stressors, and (ii) if there is a consequent loss of social resilience, reflected in colony fitness (survival, growth and reproduction). We monitored stressed (high load of the parasitic mite Varroa destructor or nutrition restricted) colonies and presumably non-stressed colonies from the beginning of 2020 till spring of 2021. We found that honeybee colonies do not shift the timing of brood rearing and nest emergence in spring as a coping mechanism to stressors. However, we show that there is loss of social resilience in stressed colonies, leading to reduced growth and reproduction. Our study contributes to better understanding the effects of stressors on social resilience in eusocial organisms.

Honeybee cluster-not insulation but stressful heat sink

Since the early twentieth century, the outer layer (mantle) of honeybees (Apis mellifera) in the winter cluster has been said to insulate the cluster core. This has encouraged enforced clustering, by the beekeepers' dominant use of inadequately insulated hives and, in North America, refrigeration. This is often seen as a benign or even a necessary process, with beekeeping and academic research considering these conditions of extreme heat loss, compared with the honeybee's natural habitat, as natural and normal. By using porous material correlations, analysis of previous findings and a model of a cluster within a hive in a landscape that implements convection, conduction and radiation, we show that a honeybee colony increases in thermal conductivity, on transition from pre-cluster to dense mantle, by a factor of approximately 2, and insulation R-value can decrease by more than 11. These results show that the mantle does not act like insulation and that clustering is not benign, but instead is an evolutionary behavioural reaction to an existential threat that results in increased cold and exertion stress. Thus the attitude to forced clustering, i.e. deliberately provoking a stressful survival behaviour, needs revision as avoidable forced stress upon animals may be regarded as cruel.

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.

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.

Seasonal changes in ultrastructure and gene expression in the fat body of worker honey bees

The anatomical, physiological, and behavioral characteristics of honey bees are affected by the season as well as division of labor. In this study, we examined the structure, ultrastructure, and gene expression of fat body cells in both long-lived winter and short-lived summer worker bees (the youngest stage of hive bees and forager bees). In contrast to hive bees, foragers and winter bees have a higher metabolism due to intensive muscle activity during their flight (foragers) or endothermic heat production (winter bees). These workers differ from hive bees in the biology of their mitochondria, peroxisomes, and lysosomes as well as in the expression of the genes involved in lipid, carbohydrate, amino acid metabolism, insulin, and TGF- β signaling. Additionally, the expression of genes related to phospholipid metabolism was higher in the hive bees. However, we found no differences between workers in the expression of genes controlling cell organelles, such as the Golgi apparatus, endoplasmic reticulum, ribosomes, nucleus, and vacuoles, as well as genes for DNA replication, cell cycle control, and autophagy. Furthermore, lysosomes, autophagic processes and lipofuscin particles were more frequently observed in winter bees using electron microscopy.

A robotic honeycomb for interaction with a honeybee colony

Robotic technologies have shown the capability to interact with living organisms and even to form integrated mixed societies composed of living and artificial agents. Biocompatible robots, incorporating sensing and actuation capable of generating and responding to relevant stimuli, can be a tool to study collective behaviors previously unattainable with traditional techniques. To investigate collective behaviors of the western honeybee (Apis mellifera), we designed a robotic system capable of observing and modulating the bee cluster using an array of thermal sensors and actuators. We initially integrated the system into a beehive populated with about 4000 bees for several months. The robotic system was able to observe the colony by continuously collecting spatiotemporal thermal profiles of the winter cluster. Furthermore, we found that our robotic device reliably modulated the superorganism's response to dynamic thermal stimulation, influencing its spatiotemporal reorganization. In addition, after identifying the thermal collapse of a colony, we used the robotic system in a "life-support" mode via its thermal actuators. Ultimately, we demonstrated a robotic device capable of autonomous closed-loop interaction with a cluster comprising thousands of individual bees. Such biohybrid societies open the door to investigation of collective behaviors that necessitate observing and interacting with the animals within a complete social context, as well as for potential applications in augmenting the survivability of these pollinators crucial to our ecosystems and our food supply.

Robustness of the honeybee neuro-muscular octopaminergic system in the face of cold stress

In recent decades, our planet has undergone dramatic environmental changes resulting in the loss of numerous species. This contrasts with species that can adapt quickly to rapidly changing ambient conditions, which require physiological plasticity and must occur rapidly. The Western honeybee (Apis mellifera) apparently meets this challenge with remarkable success, as this species is adapted to numerous climates, resulting in an almost worldwide distribution. Here, coordinated individual thermoregulatory activities ensure survival at the colony level and thus the transmission of genetic material. Recently, we showed that shivering thermogenesis, which is critical for honeybee thermoregulation, depends on octopamine signaling. In this study, we tested the hypothesis that the thoracic neuro-muscular octopaminergic system strives for a steady-state equilibrium under cold stress to maintain endogenous thermogenesis. We can show that this applies for both, octopamine provision by flight muscle innervating neurons and octopamine receptor expression in the flight muscles. Additionally, we discovered alternative splicing for AmOARβ2. At least the expression of one isoform is needed to survive cold stress conditions. We assume that the thoracic neuro-muscular octopaminergic system is finely tuned in order to contribute decisively to survival in a changing environment.

Community Dynamics in Structure and Function of Honey Bee Gut Bacteria in Response to Winter Dietary Shift

Temperate honey bees (Apis mellifera) are challenged by low temperatures and abrupt dietary shifts associated with behavioral changes during winter. Case studies have revealed drastic turnover in the gut microbiota of winter bees, highlighted by the seasonal dominance of a non-core bacterium Bartonella. However, neither biological consequence nor underlying mechanism of this microbial turnover is clear. In particular, we ask whether such changes in gut profile are related to winter dietary shift and possibly beneficial to host and associated gut microbiome? Here, we integrated evidences from genomics, metagenomics, and metabolomics in three honey bee subspecies maintained at the same locality of northern China to profile both diversity and functional variations in gut bacteria across seasons. Our results showed that winter dominance of Bartonella was shared in all tested honey bee lineages. This seasonal change was likely a consequence of winter dietary shifts characterized by greatly reduced pollen consumption and accumulation of metabolic waste due to restricted excretion. Bartonella showed expanded genomic capacity in utilizing more diverse energy substrates, such as converting metabolic wastes lactate and ethanol into pyruvate, an energy source for self-utilization and possibly also for host and other symbionts. Furthermore, Bartonella was the only bacterium capable of both producing and secreting tryptophan and phenylalanine, whose metabolic products were detected in bee guts, even though all gut bacteria lacked relevant digestion enzymes. These results thus suggested a possible mechanism where the gut bacteria might benefit the host by supplementing them with essential amino acids lacking in a protein shortage diet.

Overwintering in North American domesticated honeybees (Apis mellifera) causes mitochondrial reprogramming while enhancing cellular immunity

Many factors negatively impact domesticated honeybee (Apis mellifera) health causing a global decrease in their population year after year with major losses occurring during winter, and the cause remains thus far unknown. Here, we monitored for 12 months North American colonies of honeybees enduring important temperature variations throughout the year, to assess the metabolism and immune system of honeybees of summer and winter individuals. Our results show that in flight muscle, mitochondrial respiration via complex I during winter is drastically reduced compared to summer. However, the capacity for succinate and glycerol-3-phosphate (G3P) oxidation by mitochondria is increased during winter, resulting in higher mitochondrial oxygen consumption when complex I substrates, succinate and G3P were assessed altogether. Pyruvate kinase, lactate dehydrogenase, aspartate aminotransferase, citrate synthase and malate dehydrogenase tend to have reduced activity levels in winter unlike hexokinase, NADH dehydrogenase and pyruvate dehydrogenase. Transcript abundance of highly important immunity proteins like Vitellogenin and Defensin-1 were also increased in winter bees, and a stronger phagocytic response as well as a better hemocyte viability was observed during winter. Thus, a reorganization of substrate utilization favoring succinate and G3P while negatively affecting complex I of the ETS is occurring during winter. We suggest that this might be due to complex I transitioning to a dormant conformation through post-translational modification. Winter bees also have an increased response for antibacterial elimination in honeybees. Overall, this study highlights previously unknown cellular mechanisms between summer and winter honeybees that further our knowledge about this important species.

Flexible Thermal Sensitivity of Mitochondrial Oxygen Consumption and Substrate Oxidation in Flying Insect Species

Mitochondria have been suggested to be paramount for temperature adaptation in insects. Considering the large range of environments colonized by this taxon, we hypothesized that species surviving large temperature changes would be those with the most flexible mitochondria. We thus investigated the responses of mitochondrial oxidative phosphorylation (OXPHOS) to temperature in three flying insects: the honeybee (Apis mellifera carnica), the fruit fly (Drosophila melanogaster) and the Colorado potato beetle (Leptinotarsa decemlineata). Specifically, we measured oxygen consumption in permeabilized flight muscles of these species at 6, 12, 18, 24, 30, 36, 42 and 45°C, sequentially using complex I substrates, proline, succinate, and glycerol-3-phosphate (G3P). Complex I respiration rates (CI-OXPHOS) were very sensitive to temperature in honeybees and fruit flies with high oxygen consumption at mid-range temperatures but a sharp decline at high temperatures. Proline oxidation triggers a major increase in respiration only in potato beetles, following the same pattern as CI-OXPHOS for honeybees and fruit flies. Moreover, both succinate and G3P oxidation allowed an important increase in respiration at high temperatures in honeybees and fruit flies (and to a lesser extent in potato beetles). However, when reaching 45°C, this G3P-induced respiration rate dropped dramatically in fruit flies. These results demonstrate that mitochondrial functions are more resilient to high temperatures in honeybees compared to fruit flies. They also indicate an important but species-specific mitochondrial flexibility for substrate oxidation to sustain high oxygen consumption levels at high temperatures and suggest previously unknown adaptive mechanisms of flying insects’ mitochondria to temperature.

Octopamine drives honeybee thermogenesis

In times of environmental change species have two options to survive: they either relocate to a new habitat or they adapt to the altered environment. Adaptation requires physiological plasticity and provides a selection benefit. In this regard, the Western honeybee (Apis mellifera) protrudes with its thermoregulatory capabilities, which enables a nearly worldwide distribution. Especially in the cold, shivering thermogenesis enables foraging as well as proper brood development and thus survival. In this study, we present octopamine signaling as a neurochemical prerequisite for honeybee thermogenesis: we were able to induce hypothermia by depleting octopamine in the flight muscles. Additionally, we could restore the ability to increase body temperature by administering octopamine. Thus, we conclude that octopamine signaling in the flight muscles is necessary for thermogenesis. Moreover, we show that these effects are mediated by β octopamine receptors. The significance of our results is highlighted by the fact the respective receptor genes underlie enormous selective pressure due to adaptation to cold climates. Finally, octopamine signaling in the service of thermogenesis might be a key strategy to survive in a changing environment.

Entomopathogenic Fungi for Pests and Predators Control in Beekeeping

The emergence of resistance to chemical drugs in beekeeping is becoming a phenomenon of widespread concern. One promising alternative to the use of chemicals is entomopathogenic organisms that are environmentally friendly and are capable of stopping the expression of resistance once it has evolved. In the recent past, the scientific community has carried out several experiments addressing the use of microbiological control agents. In particular, experimental studies using entomopathogenic fungi have had more success in honey bee research. With their adherence properties and their ability to digest the cuticle and overcome the host defense mechanism, they could be a suitable ingredient in bioacaricides. Several promising fungi have been identified in the search for effective means to control pest populations. The data obtained from the different experiments are interesting and often favorable to their use, but there are also conflicting results. The aim of this review is to describe the state of the art on the topic under investigation.

Warmer winters are associated with lower levels of the cryoprotectant glycerol, a slower decrease in vitellogenin expression and reduced virus infections in winter honeybees

Within the context of climate change, winter temperatures at high latitudes are predicted to rise faster than summer temperatures. This phenomenon is expected to negatively affect the diapause performance and survival of insects, since they largely rely on low temperatures to lower their metabolism and preserve energy. However, some insects like honeybees, remain relatively active during the winter and elevate their metabolic rate to produce endothermic heat when temperatures drop. Warming winters are thus expected to improve overwintering performance of honeybees. In order to verify this hypothesis, for two consecutive years, we exposed honeybee colonies to either a mild or cold winter. We then monitored the influence of wintering conditions on several parameters of honeybee overwintering physiology, such as levels of the cryoprotectant glycerol, expression levels of immune and antioxidant genes, and genes encoding multifunctional proteins, including vitellogenin, which promotes bee longevity. Winter conditions had no effect on the expression of antioxidant genes, and genes related to immunity were not consistently affected. However, mild winters were consistently associated with a lower investment in glycerol synthesis and a higher expression of fat body genes, especially apidaecin and vitellogenin. Finally, while we found that viral loads generally decreased through the winter, this trend was more pronounced under mild winter conditions. In conclusion, and without considering how warming temperatures might affect other aspects of honeybee biology before overwintering, our data suggest that warming temperatures will likely benefit honeybee vitality by notably reducing their viral loads over the winter.

Understanding social resilience in honeybee colonies

Honeybee colonies experience high losses, induced by several stressors that can result in the collapse of colonies. Experiments show what effects stressors, such as parasites, pathogens and pesticides, can have on individual honeybees as well as colonies. Although individuals may die, colonies do not always collapse from such disturbances. As a superorganism, the colony can maintain or return back to homeostasis through colony mechanisms. This capacity is defined as social resilience. When the colony faces a high stress load, this may lead to breakdown in mechanisms, loss in resilience and eventually colony collapse. Before social resilience can be measured in honeybees, we need to examine the mechanisms in colonies that allow recovery and maintenance after stressor exposure. Here, we discuss some of these mechanisms and how they affect the social resilience of honeybee colonies. Understanding social resilience in honeybees is essential to managing colony health and loss prevention.

Winter weight loss of different subspecies of honey bee Apis mellifera colonies (Linnaeus, 1758) in southwestern Sweden

Honey bees are currently facing mounting pressures that have resulted in population declines in many parts of the world. In northern climates winter is a bottleneck for honey bees and a thorough understanding of the colonies’ ability to withstand the winter is needed in order to protect the bees from further decline. In this study the influence of weather variables on colony weight loss was studied over one winter (2019–2020) in two apiaries (32 colonies in total) in southwestern Sweden with weather stations recording wind and temperature at 5-min intervals. Three subspecies of honey bees and one hybrid were studied: the native Apis mellifera mellifera, the Italian A. m. ligustica, the Carniolan A. m. carnica and the hybrid Buckfast. Additionally, we recorded Varroa mite infestation. To analyze factors involved in resource consumption, three modelling approaches using weather and weight data were developed: the first links daily consumption rates with environmental variables, the second modelled the cumulative weight change over time, and the third estimated weight change over time taking light intensity and temperature into account. Weight losses were in general low (0.039 ± 0.013kg/day and colony) and comparable to southern locations, likely due to an exceptionally warm winter (average temperature 3.5°C). Weight losses differed only marginally between subspecies with indications that A. m. mellifera was having a more conservative resource consumption, but more studies are needed to confirm this. We did not find any effect of Varroa mite numbers on weight loss. Increased light intensity and temperature both triggered the resource consumption in honey bees. The temperature effect on resource consumption is in accordance with the metabolic theory of ecology. The consequences of these findings on honey bee survival under predicted climate changes, is still an open question that needs further analysis.

A biophysical approach to assess weather impacts on honey bee colony winter mortality

The western honey bee (Apis mellifera) is one of the most important insects kept by humans, but high colony losses are reported around the world. While the effects of general climatic conditions on colony winter mortality were already demonstrated, no study has investigated specific weather conditions linked to biophysical processes governing colony vitality. Here, we quantify the comparative relevance of four such processes that co-determine the colonies' fitness for wintering during the annual hive management cycle, using a 10-year dataset of winter colony mortality in Austria that includes 266 378 bee colonies. We formulate four process-based hypotheses for wintering success and operationalize them with weather indicators. The empirical data is used to fit simple and multiple linear regression models on different geographical scales. The results show that approximately 20% of winter mortality variability can be explained by the analysed weather conditions, and that it is most sensitive to the duration of extreme cold spells in mid and late winter. Our approach shows the potential of developing weather indicators based on biophysical processes and discusses the way forward for applying them in climate change studies.

The Role of Colony Temperature in the Entrainment of Circadian Rhythms of Honey Bee Foragers

Honey bees utilize their circadian rhythms to accurately predict the time of day. This ability allows foragers to remember the specific timing of food availability and its location for several days. Previous studies have provided strong evidence toward light/dark cycles being the primary Zeitgeber for honey bees. Work in our laboratory described large individual variation in the endogenous period length of honey bee foragers from the same colony and differences in the endogenous rhythms under different constant temperatures. In this study, we further this work by examining the temperature inside the honey bee colony. By placing temperature and light data loggers at different locations inside the colony we measured temperature at various locations within the colony. We observed significant oscillations of the temperature inside the hive, that show seasonal patterns. We then simulated the observed temperature oscillations in the laboratory and found that using the temperature cycle as a Zeitgeber, foragers present large individual differences in the phase of locomotor rhythms for temperature. Moreover, foragers successfully synchronize their locomotor rhythms to these simulated temperature cycles. Advancing the cycle by six hours, resulting in changes in the phase of activity in some foragers in the assay. The results are shown in this study highlight the importance of temperature as a potential Zeitgeber in the field. Future studies will examine the possible functional and evolutionary role of the observed phase differences of circadian rhythms.

Worker Size Diversity Has No Effect on Overwintering Success under Natural Conditions in the Ant Temnothorax nylanderi

Simple Summary

Winter is a harsh season for organisms living in temperate zones. Winter is often associated with starvation and cold temperatures, and these pressures can strongly affect organism survival. Living in groups can help these animals to cope with winter pressures. Social groups contain individuals which can vary in different ways: physiology, behavior, morphology, etc. In social insects such as ants, worker size leads to different responses to starvation and cold temperature in the laboratory. In this study, we investigated whether worker size affects colony and individual survival under natural conditions. We manipulated both worker size diversity and mean worker size within colonies of the ant Temnothorax nylanderi, reintroduced them in the field, and measured colony survival after overwintering. We found similar colony and individual (both adults and young) survival during winter between treatment colonies with reduced size diversity and/or manipulated mean worker size compared to control colonies with unmanipulated worker size. This result highlights that worker size diversity has no influence on colony performance in this species and more broadly questions the interest of worker size in social insect species with moderate worker size diversity. We discuss the potential sources of worker size diversity, including social context and selfish behavior.

Abstract

Winter is a difficult period for animals that live in temperate zones. It can inflict high mortality or induce weight loss with potential consequences on performance during the growing season. Social groups include individuals of various ages and sizes. This diversity may improve the ability of groups to buffer winter disturbances such as starvation or cold temperature. Studies focusing on the buffering role of social traits such as mean size and diversity of group members under winter conditions are mainly performed in the laboratory and investigate the effect of starvation or cold separately. Here, we experimentally decreased worker size diversity and manipulated worker mean size within colonies in order to study the effect on overwintering survival in the ant Temnothorax nylanderi. Colonies were placed under natural conditions during winter. Colony survival was high during winter and similar in all treatments with no effect of worker size diversity and mean worker size. Higher brood survival was positively correlated with colony size (i.e., the number of workers). Our results show that the higher resistance of larger individuals against cold or starvation stresses observed in the laboratory does not directly translate into higher colony survival in the field. We discuss our results in the light of mechanisms that could explain the possible non-adaptive size diversity in social species.

Coping with the cold and fighting the heat: thermal homeostasis of a superorganism, the honeybee colony

The worldwide distribution of honeybees and their fast propagation to new areas rests on their ability to keep up optimal ‘tropical conditions’ in their brood nest both in the cold and in the heat. Honeybee colonies behave like ‘superorganisms’ where individuals work together to promote reproduction of the colony. Social cooperation has developed strongly in thermal homeostasis, which guarantees a fast and constant development of the brood. We here report on the cooperation of individuals in reaction to environmental variation to achieve thermal constancy of 34–36 °C. The measurement of body temperature together with bee density and in-hive microclimate showed that behaviours for hive heating or cooling are strongly interlaced and differ in their start values. When environmental temperature changes, heat production is adjusted both by regulation of bee density due to migration activity and by the degree of endothermy. Overheating of the brood is prevented by cooling with water droplets and increased fanning, which start already at moderate temperatures where heat production and bee density are still at an increased level. This interlaced change and onset of different thermoregulatory behaviours guarantees a graded adaptation of individual behaviour to stabilise the temperature of the brood.

Adaptations to thermal stress in social insects: recent advances and future directions

Thermal stress is a major driver of population declines and extinctions. Shifts in thermal regimes create new environmental conditions, leading to trait adaptation, population migration, and/or species extinction. Extensive research has examined thermal adaptations in terrestrial arthropods. However, little is known about social insects, despite their major role in ecosystems. It is only within the last few years that the adaptations of social insects to thermal stress have received attention. Herein, we discuss what is currently known about thermal tolerance and thermal adaptation in social insects - namely ants, termites, social bees, and social wasps. We describe the behavioural, morphological, physiological, and molecular adaptations that social insects have evolved to cope with thermal stress. We examine individual and collective responses to both temporary and persistent changes in thermal conditions and explore the extent to which individuals can exploit genetic variability to acclimatise. Finally, we consider the costs and benefits of sociality in the face of thermal stress, and we propose some future research directions that should advance our knowledge of individual and collective thermal adaptations in social insects.

Phages in Therapy and Prophylaxis of American Foulbrood - Recent Implications From Practical Applications

American foulbrood is one of the most serious and yet unsolved problems of beekeeping around the world, because it causes a disease leading to the weakening of the vitality of honey bee populations and huge economic losses both in agriculture and horticulture. The etiological agent of this dangerous disease is an extremely pathogenic spore-forming bacterium, Paenibacillus larvae, which makes treatment very difficult. What is more, the use of antibiotics in the European Union is forbidden due to restrictions related to the prevention of the presence of antibiotic residues in honey, as well as the global problem of spreading antibiotic resistance in case of bacterial strains. The only available solution is burning of entire bee colonies, which results in large economic losses. Therefore, bacteriophages and their lytic enzymes can be a real effective alternative in the treatment and prevention of this Apis mellifera disease. In this review, we summarize phage characteristics that make them a potentially useful tool in the fight against American foulbrood. In addition, we gathered data regarding phage application that have been described so far, and attempted to show practical implications and possible limitations of their usage.

Large- and Small-Scale Environmental Factors Drive Distributions of Ant Mound Size Across a Latitudinal Gradient

Red wood ants are keystone species of forest ecosystems in Europe. Environmental factors and habitat characteristics affect the size of their nest mounds, an important trait being in concordance with a colony’s well-being and impact on its surroundings. In this study, we investigated the effect of large-scale (latitude and altitude) and small-scale environmental factors (e.g., characteristics of the forest) on the size of nest mounds of Formica polyctena in Central Europe. We predicted that the change in nest size is in accordance with Bergmann’s rule that states that the body size of endotherm animals increases with the higher latitude and/or altitude. We found that the size of nests increased along the latitudinal gradient in accordance with Bergmann’s rule. The irradiation was the most important factor responsible for the changes in nest size, but temperature and local factors, like the perimeter of the trees and their distance from the nest, were also involved. Considering our results, we can better understand the long-term effects and consequences of the fast-changing environmental factors on this ecologically important group. This knowledge can contribute to the planning of forest management tactics in concordance with the assurance of the long-term survival of red wood ants.

Dynamics of pattern formation and emergence of swarming in Caenorhabditis elegans

Many animals collectively form complex patterns to tackle environmental difficulties. Several biological and physical factors, such as animal motility, population densities, and chemical cues, play significant roles in this process. However, very little is known about how sensory information interplays with these factors and controls the dynamics of pattern formation. Here, we study the direct relation between oxygen sensing, pattern formation, and emergence of swarming in active Caenorhabditis elegans aggregates. We find that when thousands of animals gather on food, bacteria-mediated decrease in oxygen level slows down the animals and triggers motility-induced phase separation. Three coupled factors—bacterial accumulation, aerotaxis, and population density—act together and control the entire dynamics. Furthermore, we find that biofilm-forming bacterial lawns including Bacillus subtilis and Pseudomonas aeruginosa strongly alter the collective dynamics due to the limited diffusibility of bacteria. Additionally, our theoretical model captures behavioral differences resulting from genetic variations and oxygen sensitivity.

Collective ventilation in honeybee nests

European honey bees ( Apis mellifera) live in large congested nest cavities with a single opening that limits passive ventilation. When the local air temperature exceeds a threshold, the nests are actively ventilated by bees fanning their wings at the nest entrance. Here, we show that colonies with relatively large nest entrances use an emergent ventilation strategy where fanning bees self-organize to form groups, separating regions of continuous inflow and outflow. The observed spatio-temporal patterns correlate the air velocity and air temperature along the entrances to the distribution of fanning bees. A mathematical model that couples these variables to known fanning behaviour of individuals recapitulates their collective dynamics. Additionally, the model makes predictions about the temporal stability of the fanning group as a function of the temperature difference between the environment and the nest. Consistent with these predictions, we observe that the fanning groups drift, cling to the entrance boundaries, break-up and reform as the ambient temperature varies over a period of days. Overall, our study shows how honeybees use flow-mediated communication to self-organize into a steady state in fluctuating environments.

Photomorphogenesis for robot self-assembly: adaptivity, collective decision-making, and self-repair

Self-assembly in biology is an inspiration for engineered large-scale multi-modular systems with desirable characteristics, such as robustness, scalability, and adaptivity. Previous works have shown that simple mobile robots can be used to emulate and study self-assembly behaviors. However, many of these studies were restricted to rather static and inflexible aggregations in predefined shapes, and were limited in adaptivity compared to that observed in nature. We propose a photomorphogenesis approach for robots using our vascular morphogenesis model-a light-stimuli directed method for multi-robot self-assembly inspired by the tissue growth of trees. Robots in the role of 'leaves' collect a virtual resource that is proportional to a real, sensed environmental feature. This is then used to build a virtual underlying network that shares a common resource throughout the whole robot aggregate and determines where it grows or shrinks as a reaction to the dynamic environment. In our approach the robots use supplemental bioinspired models to collectively select a leading robot to decide who starts to self-assemble (and where), or to assemble static aggregations. The robots then use our vascular morphogenesis model to aggregate in a directed way preferring bright areas, hence resembling natural phototropism (growth towards light). Our main result is that the assembled robots are adaptive and able to react to dynamic environments by collectively and autonomously rearranging the aggregate, discarding outdated parts, and growing new ones. In representative experiments, the self-assembling robots collectively make rational decisions on where to grow. Cutting off parts of the aggregate triggers a self-organizing repair process in the robots, and the parts regrow. All these capabilities of adaptivity, collective decision-making, and self-repair in our robot self-assembly originate directly from self-organized behavior of the vascular morphogenesis model. Our approach opens up opportunities for self-assembly with reconfiguration on short time-scales with high adaptivity of dynamic forms and structures.

pH-dependent stability of honey bee (Apis mellifera) major royal jelly proteins

Honey bee larval food jelly is a secretion of the hypopharyngeal and mandibular glands of young worker bees that take care of the growing brood in the hive. Food jelly is fed to all larvae (workers, drones and queens) and as royal jelly to the queen bee for her entire life. Up to 18% of the food jelly account for proteins the majority of which belongs to the major royal jelly protein (MRJP) family. These proteins are produced in the hypopharyngeal glands at a pH value of 7.0. Before being fed to the larvae, they are mixed with the fatty acids secreted by the mandibular glands of the worker bees resulting at a pH of 4.0 in the food jelly. Thus, MRJPs are exposed to a broad pH range from their site of synthesis to the actual secreted larval food. We therefore determined the pH-dependent stability of MRJP1, MRJP2 and MRJP3 purified from royal jelly using differential scanning fluorimetry. All MRJPs were much more stable at acidic pH values compared to neutral ones with all proteins showing highest stability at pH 4.0 or 4.5, the native pH of royal jelly.

Scientific Note: Warming Nurses, a New Worker Role Recorded for the First Time in Stingless Bees

Nest temperature is a crucial variable that determines colony survival in social insects. The successful production and development of a new brood, therefore, depends on stable thermal conditions and limited temperature oscillations. Thermoregulatory processes are useful in controlling both individual activity and for the maintenance of colony temperature. We measured heat production generated by nurse bees working on brood combs of the stingless bee Melipona scutellaris (Hymenoptera, Apidae, Meliponini) in this study; our results enabled us to identify the existence of a new task performed by nurse bees, referred to here as 'hot bees' because of their higher thorax surface temperature (4°C above that of other bees within the brood area). This additional heat has been little studied in stingless bees but is likely the result of thorax muscle contractions or, indeed, the development of this musculature as these are recently emerged individuals. We hypothesize that these 'hot bees' contribute to the maintenance of warmth within the nest brood area.

Thermal efficiency extends distance and variety for honeybee foragers: analysis of the energetics of nectar collection and desiccation by Apis mellifera

The desiccation of nectar to produce honey by honeybees ( Apis mellifera L.) is an energy-intensive process, as it involves a quasi-isothermal change in the concentration of sugars from typically 20 to 80% by vaporization (honey ripening). This analysis creates mathematical models for: the collected nectar to honey ratio; energy recovery ratio; honey energy margin; and the break-even distance, which includes the factors of nectar concentration and the distance to the nectar from the nest; energetics of desiccation and a new factor, thermal energy efficiency (TEE) of nectar desiccation. These models show a significant proportion of delivered energy in the nectar must be used in desiccation, and that there is a strong connection between TEE and nest lumped thermal conductance with colony behaviour. They show the connection between TEE and honeybee colony success, or failure, in the rate of return, in terms of distance or quality of foraging. Consequently, TEE is a key parameter in honeybee populations and foraging modelling. For bee keeping, it quantifies the summer benefits of a key hive design parameter, hive thermal conductance and gives a sound theoretical basis for improving honey yields, as seen in expanded polystyrene hives.

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

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

Developmental changes in gene expression and enzyme activities of anabolic and catabolic enzymes for storage carbohydrates in the honeybee, Apis mellifera

Glycogen and trehalose are important sources of energy in insects. The expression of genes encoding the key metabolic enzymes-glycogen synthase (GS), glycogen phosphorylase (GP), trehalose-6-phosphate synthase (TPS-1), soluble trehalase (Tre-1) and membrane-bound trehalase (Tre-2)-was analyzed in 12 developmental stages of Apis mellifera worker brood. The content of GS and GP proteins, TPS activity, total trehalase activity, and the activity of Tre-1 and Tre-2 were determined. Transcript quantity was not always correlated with the content of the encoded GS or GP protein. The correlation was higher for GS (r = 0.797) than GP (r = 0.651). The expression of the glycogen synthase gene (gs) and the glycogen phosphorylase gene (gp) was high in 4- and 7-day-old larvae and in pupae, excluding the last pupal stage. The expression of the tps-1 gene was highest in the mid-pupal stage and contributed to higher enzyme activity in that stage. The expression of the tre-1 gene was higher than the expression of the tre-2 gene throughout development. In newly hatched workers, the expression of genes encoding catabolic enzymes of both carbohydrates, gp and tre-1, was higher than the expression of genes encoding anabolic enzymes. The results of this study suggest that sugar metabolism genes have somewhat different control mechanisms during larval development and metamorphosis.

Validation of quantitative real-time PCR reference genes for the determination of seasonal and labor-specific gene expression profiles in the head of Western honey bee, Apis mellifera

Honey bee is not only considered an important pollinator in agriculture, but is also widely used as a model insect in biological sciences, thanks to its highly evolved sociality, specialization of labor division, and flexibility of colony management. For an intensive investigation of the seasonal and labor-dependent expression patterns of its genes, accurate quantification of the target gene transcription level is a fundamental step. To date, quantitative real-time PCR (qRT-PCR) has been widely used for rapid quantification of gene transcripts, with reliable reference gene(s) for normalization. To this end, in an attempt to search for reliable reference genes, the amplification efficiencies of six candidate reference genes (rp49, rpL32, rpS18, tbp, tub, and gapdh) were determined. Subsequently, four genes (rpL32, rpS18, tbp, and gapdh) with PCR efficiencies of 90% to 110% were evaluated for their expression stabilities with three programs (geNorm, NormFinder, and BestKeeper) and used for normalization of seasonal expression patterns of target genes in the forager and nurse heads. Although the three programs revealed slightly different results, two genes, rpS18 and gapdh, were suggested to be the optimal reference genes for qRT-PCR-based determination of seasonal and labor-specific gene expression profiles. Furthermore, the combined use of these two genes yielded a more accurate normalization, compared with the use of a single gene in the head of honey bee. The validated reference genes can be widely used for quantification of target gene expression in honey bee head although it is still remained to be elucidated the expression levels of the selected reference genes in specific tissues in head.

Seasonality of honey bee (Apis mellifera) micronutrient supplementation and environmental limitation

Honey bees (Apis mellifera) obtain micronutrients from floral resources and "dirty", or turbid, water. Past research suggests that honey bees drink dirty water to supplement the micronutrients in their floral diet, however, there is no research that directly investigates how floral micronutrient content varies with water preferences, or how micronutrients in honey bees themselves vary seasonally. In this study, we used chemical analyses (ICP-OES) to investigate seasonal variation of micronutrients in honey bee workers and floral resources in the field. We found that honey bees likely use mineralized water to supplement their floral diet and may be limited by availability of calcium and potassium. Our results also suggest that honey bees may seasonally seek specific micronutrients, perhaps in preparation for overwintering.

Abscisic acid enhances cold tolerance in honeybee larvae

The natural composition of nutrients present in food is a key factor determining the immune function and stress responses in the honeybee (Apis mellifera). We previously demonstrated that a supplement of abscisic acid (ABA), a natural component of nectar, pollen, and honey, increases honeybee colony survival overwinter. Here we further explored the role of ABA in in vitro-reared larvae exposed to low temperatures. Four-day-old larvae (L4) exposed to 25°C for 3 days showed lower survival rates and delayed development compared to individuals growing at a standard temperature (34°C). Cold-stressed larvae maintained higher levels of ABA for longer than do larvae reared at 34°C, suggesting a biological significance for ABA. Larvae fed with an ABA-supplemented diet completely prevent the low survival rate due to cold stress and accelerate adult emergence. ABA modulates the expression of genes involved in metabolic adjustments and stress responses: Hexamerin 70b, Insulin Receptor Substrate, Vitellogenin, and Heat Shock Proteins 70. AmLANCL2, the honeybee ABA receptor, is also regulated by cold stress and ABA. These results support a role for ABA increasing the tolerance of honeybee larvae to low temperatures through priming effects.

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.

TRPA1 Channels in Drosophila and Honey Bee Ectoparasitic Mites Share Heat Sensitivity and Temperature-Related Physiological Functions

The transient receptor potential cation channel, subfamily A, member 1 (TRPA1) is conserved between many arthropods, and in some has been shown to function as a chemosensor for noxious compounds. Activation of arthropod TRPA1 channels by temperature fluctuations has been tested in only a few insect species, and all of them were shown to be activated by heat. The recent identification of chemosensitive TRPA1 channels from two honey bee ectoparasitic mite species (VdTRPA1 and TmTRPA1) have provided an opportunity to study the temperature-dependent activation and the temperature-associated physiological functions of TRPA1 channels in non-insect arthropods. We found that both mite TRPA1 channels are heat sensitive and capable of rescuing the temperature-related behavioral defects of a Drosophila melanogaster trpA1 mutant. These results suggest that heat-sensitivity of TRPA1 could be conserved between many arthropods despite its amino acid sequence diversity. Nevertheless, the ankyrin repeats (ARs) 6 and 7 are well-conserved between six heat-sensitive arthropod TRPA1 channels and have critical roles for the heat activation of VdTRPA1.

Effects of a neonicotinoid pesticide on thermoregulation of African honey bees (Apis mellifera scutellata)

Thiamethoxam is a widely used neonicotinoid pesticide that, as agonist of the nicotinic acetylcholine receptors, has been shown to elicit a variety of sublethal effects in honey bees. However, information concerning neonicotinoid effects on honey bee thermoregulation is lacking. Thermoregulation is an essential ability for the honey bee that guarantees the success of foraging and many in-hive tasks, especially brood rearing. We tested the effects of acute exposure to thiamethoxam (0.2, 1, 2ng/bee) on the thorax temperatures of foragers exposed to low (22°C) and high (33°C) temperature environments. Thiamethoxam significantly altered honey bee thorax temperature at all doses tested; the effects elicited varied depending on the environmental temperature and pesticide dose to which individuals were exposed. When bees were exposed to the high temperature environment, the high dose of thiamethoxam increased their thorax temperature 1-2h after exposure. When bees were exposed to the low temperature, the higher doses of the neonicotinoid reduced bee thorax temperatures 60-90min after treatment. In both experiments, the neonicotinoid decreased the temperature of bees the day following the exposure. After a cold shock (5min at 4°C), the two higher doses elicited a decrease of the thorax temperature, while the lower dose caused an increase, compared to the control. These alterations in thermoregulation caused by thiamethoxam may affect bee foraging activity and a variety of in-hive tasks, likely leading to negative consequences at the colony level. Our results shed light on sublethal effect of pesticides which our bees have to deal with.

Evidence for Ventilation through Collective Respiratory Movements in Giant Honeybee (Apis dorsata) Nests

The Asian giant honeybees (Apis dorsata) build single-comb nests in the open, which makes this species particularly susceptible to environmental strains. Long-term infrared (IR) records documented cool nest regions (CNR) at the bee curtain (n_CNR = 207, n_nests > 20) distinguished by marked negative gradients (ΔT_CNR/d < -3°C / 5 cm) at their margins. CNRs develop and recede within minutes, predominantly at higher ambient temperatures in the early afternoon. The differential size (ΔA_CNR) and temperature (ΔT_CNR) values per time unit correlated mostly positively (R_AT > 0) displaying the Venturi effect, which evidences funnel properties of CNRs. The air flows inwards through CNRs, which is verified by the negative spatial gradient ΔT_CNR/d, by the positive grading of T_CNR with T_amb and lastly by fanners which have directed their abdomens towards CNRs. Rare cases of R_AT < 0 (< 3%) document closing processes (for ΔA_CNR/Δt < -0.4 cm²/s) but also suggest ventilation of the bee curtain (for ΔA_CNR/Δt > +0.4 cm²/s) displaying “inhalation” and “exhalation” cycling. “Inhalation” could be boosted by bees at the inner curtain layers, which stretch their extremities against the comb enlarging the inner nest lumen and thus causing a pressure fall which drives ambient air inwards through CNR funnels. The relaxing of the formerly “activated” bees could then trigger the “exhalation” process, which brings the bee curtain, passively by gravity, close to the comb again. That way, warm, CO₂-enriched nest-borne air is pressed outwards through the leaking mesh of the bee curtain. This ventilation hypothesis is supported by IR imaging and laser vibrometry depicting CNRs in at least four aspects as low-resistance convection funnels for maintaining thermoregulation and restoring fresh air in the nest.

Effects of Pesticide Treatments on Nutrient Levels in Worker Honey Bees (Apis mellifera)

Honey bee colony loss continues to be an issue and no factor has been singled out as to the cause. In this study, we sought to determine whether two beekeeper-applied pesticide products, tau-fluvalinate and Fumagilin-B^®, and one agrochemical, chlorothalonil, impact the nutrient levels in honey bee workers in a natural colony environment. Treatments were performed in-hive and at three different periods (fall, spring, and summer) over the course of one year. Bees were sampled both at pre-treatment and two and four weeks post-treatment, weighed, and their protein and carbohydrate levels were determined using BCA and anthrone based biochemical assays, respectively. We report that, based on the pesticide concentrations tested, no significant negative impact of the pesticide products was observed on wet weight, protein levels, or carbohydrate levels of bees from treated colonies compared with bees from untreated control colonies.

A protocol for analysing thermal stress in insects using infrared thermography

The study of insect responses to thermal stress has involved a variety of protocols and methodologies that hamper the ability to compare results between studies. For that reason, the development of a protocol to standardize thermal assays is necessary. In this sense, infrared thermography solves some of the problems allowing us to take continuous temperature measurements without handling the individuals, an important fact in cold-blooded organisms like insects. Here, we present a working protocol based on infrared thermography to estimate both cold and heat thermal stress in insects. We analyse both the change in the body temperature of individuals and their behavioural response. In addition, we used partial least squares regression for the statistical analysis of our data, a technique that solves the problem of having a large number of variables and few individuals, allowing us to work with rare or endemic species. To test our protocol, we chose two species of congeneric, narrowly distributed dung beetles that are endemic to the southeastern part of the Iberian Peninsula. With our protocol we have obtained five variables in the response to cold and twelve in the response to heat. With this methodology we discriminate between the two flightless species of Jekelius through their thermal response. In response to cold, Jekelius hernandezi showed a higher rate of cooling and reached higher temperatures of stupor and haemolymph freezing than Jekelius punctatolineatus. Both species displayed similar thermoregulation ranges before reaching lethal body temperature with heat stress. Overall, we have demonstrated that infrared thermography is a suitable method to assess insect thermal responses with a high degree of sensitivity, allowing for the discrimination between closely related species.

The Potential of Bee-Generated Carbon Dioxide for Control of Varroa Mite (Mesostigmata: Varroidae) in Indoor Overwintering Honey bee (Hymenoptera: Apidae) Colonies

The objective of this study was to manipulate ventilation rate to characterize interactions between stocks of honey bees (Apis mellifera L.) and ventilation setting on varroa mite (Varroa destructor Anderson and Trueman) mortality in honey bee colonies kept indoors over winter. The first experiment used colonies established from stock selected locally for wintering performance under exposure to varroa (n = 6) and unselected bees (n = 6) to assess mite and bee mortality and levels of carbon dioxide (CO2) and oxygen (O2) in the bee cluster when kept under a simulated winter condition at 5°C. The second experiment, used colonies from selected bees (n = 10) and unselected bees (n = 12) that were exposed to either standard ventilation (14.4 liter/min per hive) or restricted ventilation (0.24 liter/min per hive, in a Plexiglas ventilation chamber) during a 16-d treatment period to assess the influence of restricted air flow on winter mortality rates of varroa mites and honey bees. Experiment 2 was repeated in early, mid-, and late winter. The first experiment showed that under unrestricted ventilation with CO2 concentrations averaging <2% there was no correlation between CO2 and varroa mite mortality when colonies were placed under low temperature. CO2 was negatively correlated with O2 in the bee cluster in both experiments. When ventilation was restricted, mean CO2 level (3.82 ± 0.31%, range 0.43-8.44%) increased by 200% relative to standard ventilation (1.29 ± 0.31%; range 0.09-5.26%) within the 16-d treatment period. The overall mite mortality rates and the reduction in mean abundance of varroa mite over time was greater under restricted ventilation (37 ± 4.2%) than under standard ventilation (23 ± 4.2%) but not affected by stock of bees during the treatment period. Selected bees showed overall greater mite mortality relative to unselected bees in both experiments. Restricting ventilation increased mite mortality, but did not affect worker bee mortality relative to that for colonies under standard ventilation. Restricted ventilation did not affect the overall level of Nosema compared with the control. However, there was an interaction between stock, season, and time of the trial. Unselected stock showed an increase in Nosema over time in the late winter trial that did not occur in the selected stock. In conclusion, these findings suggested that restricted ventilation has potential to suppress varroa mite in overwintering honey bee colonies via a low-cost and environmentally friendly measure.