Body size differs in workers produced across time and is associated with variation in the quantity and composition of larval food in <Emphasis Type="Italic">Nannotrigona perilampoides</Emphasis> (Hymenoptera,Meliponini)

Although variation in body size has been recently reported in stingless bees (Meliponini), empirical evidence evaluating possible factors related to such variation is lacking, and thus it is not clear if it may have an adaptive significance. We evaluated if variation in the body size and weight of workers of stingless bees fluctuates across a seasonal pattern and if this could be related to characteristics of the food consumed during the larval stage. The weight of larval provisions, their protein, and sugar content were evaluated in four colonies of Nannotrigona perilampoides every 2 months across 1 year. Worker-destined larvae from the same combs were allowed to develop and were sampled as callow workers to determine their weight and size using morphometric data. The weight and size of workers were highly correlated and varied across the seasons in established colonies, suggesting that size variation cycles across the year in stingless bees. An increase in the protein content and, to a lesser degree, the quantity of larval food were positively linked to variation in body weight and size; food with richer protein content resulted in larger and heavier workers. This study provides the first evidence of an effect of the quantity and composition of larval food on the size of workers in stingless bees. Although body weight and size of workers differed across seasons, they were not readily noticeable as changes seem to occur as a continuum across the year. Since size polymorphism was of a larger magnitude across time but not within age cohorts and as it was highly determined by food resources, it may not be an adaptive feature in stingless bees. However, more studies are needed to determine the role of the cyclical change in worker body size on colony performance and thus its adaptive significance in stingless bees.     

Circadian Activity Rhythm of the Foragers of a Eusocial Bee (Scaptotrigona aff depilis,Hymenoptera, Apidae,Meliponinae) outside the Nest

In all bee colonies of the Meliponinae subfamily, activity inside the nest is temporally organized around the oviposition by the queen, assisted by nurse bees. This class is constituted by young bees that remain inside the nest. In a colony of Scaptotrigona aff depilis, the oviposition cycle occurs in a 3-hour period. The foragers are older bees that collect food for the colony in the field. Other tasks in the nest are performed by workers of ages intermediate between nurses and foragers. With the aim of studying activity rhythms, foragers were kept under constant light, with food constantly available and no flight restriction. The results showed that, although inside the nest the prevailing period is 3 hours, the activity of the foragers is a circadian rhythm, synchronized by the light/dark cycle and probably influenced by other environmental cycles as temperature and the availability of food sources.     

Ecological meta‐networks integrate spatial and temporal dynamics of plant–bumble bee interactions

Bumble bees can forage on a large number of wild plants and crops. The survival of a colony depends on the availability of suitable food resources within foraging range and throughout their forage season. We studied the spatial and temporal use of floral resources by bumble bees in a set of 30 local plant communities and used these data to model colony survival under different combinations of patch size and bumble bee flight distance. Floral resources vary spatially and temporally at the landscape level, and bumble bees track these resources across the landscape during the season. The simulation model showed that different patterns of resources availability could affect the survival and distribution of bumble bee nests across the landscape. This model can be used to generate hypotheses explaining bumble bee richness and abundance that can be tested in real landscapes. Integrating the spatial and temporal dynamics of the flower resources used by bumble bees provides a new perspective that can be used to inform bumble bee conservation, particularly in the context of their widespread decline in recent decades.     

Odor information transfer in the stingless bee<Emphasis Type="Italic"> Melipona quadrifasciata</Emphasis>: effect of in-hive experiences on classical conditioning of proboscis extension

A recent study showed that the stingless bee Melipona quadrifasciata could learn to discriminate odors in a classical conditioning of proboscis extension response (PER). Here we used this protocol to investigate the ability of these bees to use olfactory information obtained within the colony in an experimental context: the PER paradigm. We compared their success in solving a classical differential conditioning depending on the previous olfactory experiences received inside the nest. We found that M. quadrifasciata bees are capable of transferring the food-odor information acquired in the colony to a differential conditioning in the PER paradigm. Bees attained higher discrimination levels when they had previously encountered the rewarded odor associated to food inside the hive. The increase in the discrimination levels, however, was in some cases unspecific to the odor used indicating a certain degree of generalization. The influence of the food scent offered at a field feeder 24 h before the classical conditioning could also be seen in the discrimination attained by the foragers in the PER setup, detecting the presence of long-term memory. Moreover, the improved performance of recruited bees in the PER paradigm suggests the occurrence of social learning of nectar scents inside the stingless bees’ hives.     

The evolution of food-producing glands in eusocial bees (Apoidea,Hymenoptera)1

A food-producing role for cephalic exocrine glands has arisen independently in both taxa of highly eusocial bees, Apis and Meliponini. With several exceptions, there is little evidence that food is produced by glands of solitary bees or by most bees at lower levels of sociality. We suggest that this association with sociality is due to four adaptive features of these glands: (1) food from the glands allows feces from queens and larvae to have a small volume, (2) the queen's fecundity can be increased, (3) nutrient recovery via cannibalism can be facilitated, and (4) rearing of emergency replacement queens is accelerated. Acceleration of the rearing of other castes and of queens in the normal process of colony fission is not clearly an advantage ascribed to these glands. Trophic eggs produced by meliponine colony workers are analogous to the secretions from food-producing glands in Meliponini and Apis workers.     

Sticking to their choice – honey bee subfamilies abandon declining food sources at a slow but uniform rate

Abstract. 1. The allocation of honey bee foragers among food patches is a result of decisions made by individual bees that are based on internal and external cues.
2. Decision-making processes are often based on internal thresholds. For example, if the quality of the food source is assessed by a forager as exceeding its internal threshold, the bee will continue foraging on that food source.
3. It is often assumed that all individuals have the same threshold and therefore use the same thresholds in decision-making, but because the honey bee queen mates with 12–30 males, the workers within a colony are genetically heterogeneous. Thus, the thresholds used by individual bees may be genetically variable within a colony.
4. Models of colony-level foraging behaviour of honey bees suggest that the rate of abandoning food sources is a critical parameter affecting foraging success. Moreover, these models show that variance among subfamilies in their abandonment rates may increase the colony's foraging efficiency.
5. Experimental data showing the relationship between the probability of abandoning a food source and its profitability are lacking, as is information on any variation in abandonment rates among subfamilies.
6. Abandonment rates were determined experimentally for four honey bee families for seven different sucrose concentrations. The results showed that abandonment rates appear to be invariant among (sub)families. The importance of forager fidelity to declining food sources is discussed with respect to foraging efficiency in a changing environment.     

Pathogenesis of varroosis at the level of the honey bee (Apis mellifera) colony

The parasitic mite Varroa destructor, in interaction with different viruses, is the main cause of honey bee colony mortality in most parts of the world. Here we studied how effects of individual-level parasitization are reflected by the bee colony as a whole. We measured disease progression in an apiary of 24 hives with differing degree of mite infestation, and investigated its relationship to 28 biometrical, physiological and biochemical indicators. In early summer, when the most heavily infested colonies already showed reduced growth, an elevated ratio of brood to bees, as well as a strong presence of phenoloxidase/prophenoloxidase in hive bees were found to be predictors of the time of colony collapse. One month later, the learning performance of worker bees as well as the activity of glucose oxidase measured from head extracts were significantly linked to the timing of colony collapse. Colonies at the brink of collapse were characterized by reduced weight of winter bees and a strong increase in their relative body water content. Our data confirm the importance of the immune system, known from studies of individually-infested bees, for the pathogenesis of varroosis at colony level. However, they also show that single-bee effects cannot always be extrapolated to the colony as a whole. This fact, together with the prominent role of colony-level factors like the ratio between brood and bees for disease progression, stress the importance of the superorganismal dimension of Varroa research.     

Colony pollen reserves affect body size,sperm production and sexual development in males of the stingless bee <Emphasis Type="Italic">Melipona beecheii</Emphasis>

The production of male sexual offspring by social insect colonies is often strongly seasonal or resource-dependent. In stingless bees, males are produced in smaller numbers under conditions of low colony food reserves; whether such males are negatively affected in traits related to reproductive success is not known. We compared body size, sperm production and sexual maturity in Melipona beecheii males reared with experimentally supplemented or reduced pollen reserves, but with otherwise equal numbers of workers and equal quantities of honey reserves. We also studied the same traits in males collected from non-manipulated colonies with pollen reserves intermediate between the supplemented or reduced groups but with more workers and honey reserves. Males reared under experimentally reduced pollen reserves had significantly smaller bodies and lower sperm counts compared to those reared in colonies with experimentally supplemented pollen reserves. There was also a significantly positive relationship between the number of sperm and body size in males across all colony treatments. The maximum number of sperm in seminal vesicles was recorded 2 days later in males from colonies with reduced pollen compared to males from colonies with supplementary pollen. Males from non-manipulated colonies were intermediate in size, sperm count and speed of maturation. Our study documents for the first time the existence of large size variation in males of stingless bees that is related with the amount of pollen reserves in their natal colony. We conclude that a colony’s pollen reserves have a major impact on male body size, sperm production and speed of sexual maturity in this stingless bee, which may be the case in other social insects. Stingless bees are a good model system to study the balance between colony-level selection and individual-level selection on male sexually selected traits such as body size.     

Social immunity in honeybees—Density dependence,diet, and body mass trade‐offs

Group living is favorable to pathogen spread due to the increased risk of disease transmission among individuals. Similar to individual immune defenses, social immunity, that is antiparasite defenses mounted for the benefit of individuals other than the actor, is predicted to be altered in social groups. The eusocial honey bee (Apis mellifera) secretes glucose oxidase (GOX), an antiseptic enzyme, throughout its colony, thereby providing immune protection to other individuals in the hive. We conducted a laboratory experiment to investigate the effects of group density on social immunity, specifically GOX activity, body mass and feeding behavior in caged honey bees. Individual honeybees caged in a low group density displayed increased GOX activity relative to those kept at a high group density. In addition, we provided evidence for a trade‐off between GOX activity and body mass: Individuals caged in the low group density had a lower body mass, despite consuming more food overall. Our results provide the first experimental evidence that group density affects a social immune response in a eusocial insect. Moreover, we showed that the previously reported trade‐off between immunity and body mass extends to social immunity. GOX production appears to be costly for individuals, and potentially the colony, given that low body mass is correlated with small foraging ranges in bees. At high group densities, individuals can invest less in social immunity than at low densities, while presumably gaining shared protection from infection. Thus, there is evidence that trade‐offs at the individual level (GOX vs. body mass) can affect colony‐level fitness.     

High Concentrations of the Alarm Pheromone Component,Isopentyl Acetate,Reduces Foraging and Dancing in <Emphasis Type="Italic">Apis mellifera</Emphasis> Ligustica and <Emphasis Type="Italic">Apis cerana</Emphasis> Cerana

A honeybee colony is a superorganism that has evolved precise communication systems, which allow the colony to gather information from numerous individuals and coordinate its behavior. Alarm pheromones, such as isopentyl acetate (IPA), the main component of sting alarm pheromone, play a critical role in the coordination of individual behaviors as well as colony communication in honeybee colonies. In this study, honeybees (Apis mellifera ligustica and Apis cerana cerana) were exposed to relatively high levels of IPA at a foraging site (6–8 bee equivalents) and inside their colony (28–58 bee equivalents) to investigate the influence of alarm pheromones on foraging activity and hive flight activity. IPA reduced the number of bees that flew out the hive, foraged, and waggle danced. Under both contexts in the hive and at the food source, IPA can therefore inhibit honey bee foraging and foraging communication.     

The colony environment, but not direct contact with conspecifics, influences the development of circadian rhythms in honey bees

Honey bee (Apis mellifera) workers emerge from the pupae with no circadian rhythms in behavior or brain clock gene expression but show strong rhythms later in life. This postembryonic development of circadian rhythms is reminiscent of that of infants of humans and other primates but contrasts with most insects, which typically emerge from the pupae with strong circadian rhythms. Very little is known about the internal and external factors regulating the ontogeny of circadian rhythms in bees or in other animals. We tested the hypothesis that the environment during early life influences the later expression of circadian rhythms in locomotor activity in young honey bees. We reared newly emerged bees in various social environments, transferred them to individual cages in constant laboratory conditions, and monitored their locomotor activity. We found that the percentage of rhythmic individuals among bees that experienced the colony environment for their first 48 h of adult life was similar to that of older sister foragers, but their rhythms were weaker. Sister bees isolated individually in the laboratory for the same period were significantly less likely to show circadian rhythms in locomotor activity. Bees experiencing the colony environment for only 24 h, or staying for 48 h with 30 same-age sister bees in the laboratory, were similar to bees individually isolated in the laboratory. By contrast, bees that were caged individually or in groups in single- or double-mesh enclosures inside a field colony were as likely to exhibit circadian rhythms as their sisters that were freely moving in the same colony. These findings suggest that the development of the circadian system in young adult honey bees is faster in the colony than in isolation. Direct contact with the queen, workers, or the brood, contact pheromones, and trophallaxis, which are all important means of communication in honey bees, cannot account for the influence of the colony environment, since they were all withheld from the bees in the double-mesh enclosures. Our results suggest that volatile pheromones, the colony microenvironment, or both influence the ontogeny of circadian rhythms in honey bees.     

Sucrose acceptance,discrimination and proboscis responses of honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.) in the field and the laboratory

Laboratory studies in honey bees have shown positive correlations between sucrose responsiveness, division of labour and learning. We tested the relationships between sucrose acceptance and discrimination in the field and responsiveness in the laboratory. Based on acceptance in the field three groups of bees were differentiated: (1) bees that accept sucrose concentrations >10%, (2) bees that accept some but not all of the sucrose concentrations <10% and water, and (3) bees that accept water and all offered sucrose concentrations. Sucrose acceptance can be described in a model in which sucrose- and water-dependent responses interact additively. Responsiveness to sucrose was tested in the same bees in the laboratory by measuring the proboscis extension response (PER). The experiments demonstrated that PER responsiveness is lower than acceptance in the field and that it is not possible to infer from the PER measurements in the laboratory those concentrations the respective bees accepted in the field. Discrimination between sucrose concentrations was tested in three groups of free-flying bees collecting low, intermediate or high concentrations of sucrose. The experiments demonstrated that bees can discriminate between concentrations differences down to 0.2 relative log units. There exist only partial correlations between discrimination, acceptance and PER responsiveness.     

Distribution of <Emphasis Type="Italic">Paenibacillus larvae</Emphasis> Spores Among Adult Honey Bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>) and the Relationship with Clinical Symptoms of American Foulbrood

Knowledge of the distribution of Paenibacillus larvae spores, the causative agent of American foulbrood (AFB), among individual adult honey bees is crucial for determining the appropriate number of adult bees to include in apiary composite samples when screening for diseased colonies. To study spore distribution at the individual bee level, 500 honey bees were collected from different parts of eight clinically diseased colonies and individually analyzed for P. larvae. From the brood chamber and from the super, bees were randomly collected and individually put in Eppendorf vials. The samples were frozen as soon as possible after collection. Concurrently with sampling, each colony was visually inspected for clinical symptoms of AFB. The number of clinically diseased cells in the colony was visually estimated. All samples were cultured in the laboratory for P. larvae. The results demonstrate that the spores are not randomly distributed among the bees; some bees have much higher spore loads than others. It is also clear that as the proportion of contaminated bees increase, the number of spores from each positive bee also increases. The data also demonstrated a relationship between the number of clinically diseased cells and the proportion of positive bees in individual colonies. This relationship was used to develop a mathematical formula for estimating the minimum number of bees in a sample to detect clinical disease. The formula takes into account the size of the apiary and the degree of certainty with which one aims to discover clinical symptoms. Calculations using the formula suggest that adult bee samples at the colony level will detect light AFB infections with a high probability. However, the skewed spore distribution of the adult bees makes composite sampling at the apiary level more problematic, if the aim of the sampling is to locate lightly infected individual colonies within apiaries. The results suggest that false-negative culturing results from composite samples of adult bees from individual colonies with clinical symptoms of AFB are highly improbable. However, if single colonies have light infections in large apiaries, the dilution effect from uncontaminated bees from healthy colonies on the positive bees from diseased colonies may yield false-negative results at the apiary level.     

Social learning of floral odours inside the honeybee hive

A honeybee hive serves as an information centre in which communication among bees allows the colony to exploit the most profitable resources in a continuously changing environment. The best-studied communication behaviour in this context is the waggle dance performed by returning foragers, which encodes information about the distance and direction to the food source. It has been suggested that another information cue, floral scents transferred within the hive, is also important for recruitment to food sources, as bee recruits are more strongly attracted to odours previously brought back by foragers in both honeybees and bumble-bees. These observations suggested that honeybees learn the odour from successful foragers before leaving the hive. However, this has never been shown directly and the mechanisms and properties of the learning process remain obscure. We tested the learning and memory of recruited bees in the laboratory using the proboscis extension response (PER) paradigm, and show that recruits indeed learn the nectar odours brought back by foragers by associative learning and retrieve this memory in the PER paradigm. The associative nature of this learning reveals that information was gained during mouth-to-mouth contacts among bees (trophallaxis). Results further suggest that the information is transferred to long-term memory. Associative learning of food odours in a social context may help recruits to find a particular food source faster.     

Effects of soybean trypsin inhibitor on hypopharyngeal gland protein content, total midgut protease activity and survival of the honey bee (Apis mellifera L.)

Insecticidal properties of protease inhibitors have been established in transgenic plants. In the wake of continuous research and rapid development of protease inhibitors it is important to assess possible effects on beneficial insects like the honey bee (Apis mellifera L.). In this study, newly emerged caged bees were fed pollen diets containing three different concentrations (0.1%, 0.5% and 1% w:w) of soybean trypsin inhibitor (SBTI). Hypopharyngeal gland protein content, total midgut proteolytic enzyme activity of these bees, and survival were measured. Bees fed 1% SBTI had significantly reduced hypopharyngeal gland protein content and midgut proteolytic enzyme activity. There were no significant differences between control, 0.1% and 0.5% SBTI treatments. Bees fed a diet containing 1% SBTI had the lowest survival, followed by 0.5% and 0.1%, over a 30-day period. We concluded that nurse bees fed a pollen diet containing at least 1% SBTI would be poor producers of larval food, potentially threatening colony growth and maintenance.     

Allocation of Colony‐Level Foraging Effort in Vespula germanica in Response to Food Resource Quantity,Quality, and Associated Olfactory Cues

In social insects, selection takes place primarily at the level of the colony. Therefore, unlike solitary insects, social species are expected to forage at rates that maximize colony fitness rather than individual fitness. Workers can increase the net benefit of foraging by responding to increased resource availability, by responding more strongly to higher‐quality resources, and by decreasing the uncertainty with which nestmates find resources. Unlike many ants and social bees, no social wasp is known to utilize a nest‐based recruitment signal to inform nestmates of food location. On the other hand, wasps do learn the odor of food brought to the nest and use this cue to locate the food source outside the nest. Here, we quantify the effects of three food‐associated variables on the allocation of foraging effort in the yellowjacket Vespula germanica. We used an experimental approach to assess whether resource quantity, quality, or associated olfactory information affect the probability that a forager will leave the nest on a foraging trip. We addressed these questions by inserting a known amount of sucrose solution directly into nests and recording foraging effort (departure rate) over the subsequent hour‐long observation period. No differences were found in foraging effort because of the presence/absence of olfactory cues, but there was strong evidence that foraging effort increased in response to resource influx and resource quality. Thus, while olfactory cues are learned in the nest, only resource quality and the cue of increased amount of food in the nest factor into a forager's decision of whether or not to depart on a foraging trip. However, as prior work has shown, once a wasp forager leaves the nest, it uses the learned olfactory cues to aid in finding resources.     

Honey bee pathology: current threats to honey bees and beekeeping

Managed honey bees are the most important commercial pollinators of those crops which depend on animal pollination for reproduction and which account for 35% of the global food production. Hence, they are vital for an economic, sustainable agriculture and for food security. In addition, honey bees also pollinate a variety of wild flowers and, therefore, contribute to the biodiversity of many ecosystems. Honey and other hive products are, at least economically and ecologically rather, by-products of beekeeping. Due to this outstanding role of honey bees, severe and inexplicable honey bee colony losses, which have been reported recently to be steadily increasing, have attracted much attention and stimulated many research activities. Although the phenomenon “decline of honey bees” is far from being finally solved, consensus exists that pests and pathogens are the single most important cause of otherwise inexplicable colony losses. This review will focus on selected bee pathogens and parasites which have been demonstrated to be involved in colony losses in different regions of the world and which, therefore, are considered current threats to honey bees and beekeeping.     

Functional flexibility of the honey bee hypopharyngeal gland in a dequeened colony

The role of the worker honey bee Apis mellifera L. changes depending on age after eclosion (age polyethism): young workers (nurse bees) take care of their brood by synthesizing and secreting brood food (royal jelly), while older workers (foragers) forage for nectar and process it into honey. Previously, we showed that the major proteins synthesized in the hypopharyngeal gland of the worker change from brood food proteins to alpha-glucosidase at the single secretory cell level in parallel with this age polyethism [Kubo et al., J. Biochem. 119, 291-295 (1996); Ohashi et al., Eur. J. Biochem. 249, 797-802 (1997)]. Here, we examined whether the function of the hypopharyngeal gland has flexibility depending on the colony conditions, by creating a dequeened colony in which the older workers were compelled to feed the drone larvae. It was found that most of the older workers in the dequeened colony synthesized brood food proteins as did nurse bees. Furthermore, the percentage of workers that synthesized brood food proteins was maintained at 80-90% of the total workers for at least two months, as in a normal colony. These results indicate that the function of the hypopharyngeal gland cells of the worker has flexibility and can, if necessary, be maintained as that of the nurse bee, depending on the condition of the colony.     

Seasonality of salt foraging in honey bees (Apis mellifera)

1. Honey bees (Apis mellifera) prefer foraging at compound‐rich, ‘dirty’, water sources over clean water sources. As a honey bee's main floral diet only contains trace amounts of micronutrients – likely not enough to sustain an entire colony – it was hypothesised that honey bees forage in dirty water for physiologically essential minerals that their floral diet, and thus the colony, may lack. 2. While there are many studies regarding macronutrient requirements of honey bees, few investigate micronutrient needs. For this study, from 2013 to 2015, a series of preference assays were conducted in both summer and autumn. 3. During all field seasons, honey bees exhibited a strong preference for sodium in comparison to deionised water. There was, however, a notable switch in preferences for other minerals between seasons. 4. Calcium, magnesium, and potassium – three minerals most commonly found in pollen – were preferred in autumn when pollen was scarce, but were avoided in summer when pollen was abundant. Thus, as floral resources change in distribution and abundance, honey bees similarly change their water‐foraging preferences. 5. Our data suggest that, although they are generalists with relatively few gustatory receptor genes, honey bee foragers are fine‐tuned to search for micronutrients. This ability likely helps the foragers in their search for a balanced diet for the colony as a whole.     

A Mathematical Model of Forager Loss in Honeybee Colonies Infested with <Emphasis Type="Italic">Varroa destructor</Emphasis> and the Acute Bee Paralysis Virus

We incorporate a mathematical model of Varroa destructor and the Acute Bee Paralysis Virus with an existing model for a honeybee colony, in which the bee population is divided into hive bees and forager bees based on tasks performed in the colony. The model is a system of five ordinary differential equations with dependent variables: uninfected hive bees, uninfected forager bees, infected hive bees, virus-free mites and virus-carrying mites. The interplay between forager loss and disease infestation is studied. We study the stability of the disease-free equilibrium of the bee-mite-virus model and observe that the disease cannot be fought off in the absence of varroacide treatment. However, the disease-free equilibrium can be stable if the treatment is strong enough and also if the virus-carrying mites become virus-free at a rate faster than the mite birth rate. The critical forager loss due to homing failure, above which the colony fails, is calculated using simulation experiments for disease-free, treated and untreated mite-infested, and treated virus-infested colonies. A virus-infested colony without varroacide treatment fails regardless of the forager mortality rate.