Colony fissioning in honey bees: size and significance of the swarm fraction

During colony founding in honey bees, a portion of a colony’s workforce (the “swarm fraction”) departs with the old mother queen in a swarm while the remaining workforce stays with a new daughter queen in the parental nest. There is little quantitative information about swarm fraction size and about how swarm fraction size affects the growth and survival of mother-queen and daughter-queen colonies. We measured (a) the swarm fraction in naturally fissioning honey bee colonies, (b) the growth and survival of mother-queen colonies as a function of swarm size, and (c) the growth and survival of mother-queen and daughter-queen colonies as a function of the swarm fraction. We found an average swarm fraction of 0.75. We also found a significant positive effect of swarm size and swarm fraction on the growth (i.e., comb built, brood produced, food stored, and weight gained) and the survival of mother-queen colonies. We found no effect of swarm fraction on the survival of daughter-queen colonies. Evidently, a honey bee colony must devote a large majority of its workforce to a swarm so that the mother-queen colony can grow sufficiently rapidly to survive its first winter.     

Benefits of recruitment in honey bees: effects of ecology and colony size in an individual-based model

Why do some social insects have sophisticated recruitment systems,while other species do not communicate about food source locationsat all? To answer this question, it is necessary to identifythe social or ecological factors that make recruitment adaptiveand thus likely to evolve. We developed an individual-basedmodel of honey bee foraging to quantify the benefits of recruitmentunder different spatial distributions of nondepleting resourcepatches and with different colony sizes. Benefits of recruitmentwere strongly dependent on resource patch quality, density,and variability. Communication was especially beneficial ifpatches were poor, few, and variable. A sensitivity analysisof the model showed that under conditions of high resource densityrecruitment could even become detrimental, especially if foragingduration was short, tendency to scout was high, or recruitsneeded a long time to find communicated locations. Colony size,a factor often suspected to influence recruitment evolution,had no significant effect. These results may explain the recentexperimental findings that in honey bees, benefits of waggledance recruitment seem to vary seasonally and with habitat.They may also explain why some, but not other, species of socialbees have evolved a strategy to communicate food locations tonest mates.     

Caste fate conflict in swarm-founding social hymenoptera: an inclusive fitness analysis

A caste system in which females develop into morphologically distinct queens or workers has evolved independently in ants, wasps and bees. Although such reproductive division of labour may benefit the colony it is also a source of conflict because individual immature females can benefit from developing into a queen in order to gain greater direct reproduction. Here we present a formal inclusive fitness analysis of caste fate conflict appropriate for swarm-founding social Hymenoptera. Three major conclusions are reached: (1) when caste is self-determined, many females should selfishly choose to become queens and the resulting depletion of the workforce can substantially reduce colony productivity; (2) greater relatedness among colony members reduces this excess queen production; (3) if workers can prevent excess queen production at low cost by controlled feeding, a transition to nutritional caste determination should occur. These predictions generalize results derived earlier using an allele-frequency model [Behav. Ecol. Sociobiol. (2001) 50: 467] and are supported by observed levels of queen production in various taxa, especially stingless bees, where caste can be either individually or nutritionally controlled.     

A spatial model of honey bee colony collapse due to pesticide contamination of foraging bees

Journal of Mathematical Biology - We develop a model of honey bee colony collapse based on contamination of forager bees in pesticide contaminated spatial environments. The model consists of...     

Altruism and relatedness at colony foundation in social insects

Cooperative nest initiation in social insects is most easily explained when cooperating females are relatives, as is common in polistine wasps. However, recent research has revealed that unrelated ant queens also initiate colonies together. Reproductive dominance hierarchies are absent among unrelated foundresses, which contrasts with the rigid dominance hierarchies found among related foundresses. New field studies of joint nest founding among non-relatives show that cooperation is favored where colonies are clumped and brood raiding is common, so that attaining a large worker force quickly is critical to colony survival. These studies enrich our understanding of the role of relatedness in social groups.     

The role of colony organization on pathogen transmission in social insects

Social organisms are especially vulnerable to pathogens due to the homogeneity of the colony, and the close proximity and extensive interactions among its members. However, the social organization of these groups also offers the potential to provide an effective barrier against the transmission of pathogens within the colony. Social insects with their elaborate colony organizations provide an ideal model system to develop and test this hypothesis. While the different elements of colony organization are generally assumed to be products of ergonomic selection, in this paper we address how the same elements could influence the transmission of pathogens. By developing a simple model, we explore how three parameters of colony organization, division of labor, interaction network and colony demography could influence the transmission of pathogens. We find that heterogeneity among individuals in terms of division of labor alone has little effect on the spread of an infection in the colony and the scenario is indistinguishable from one in which all the individuals are homogeneous. However, division of labor, combined with heterogeneity in the interaction network and demographic schedules reduce the spread of an infection.     

Interspecific and conspecific colony mergers in the dwarf honey bees Apis andreniformis and A. florea

The dwarf honey bees Apis florea and A. andreniformis are sympatric in southeast Asia. We translocated eight A. florea colonies and four A. andreniformis colonies to an orchard near Sai Yoke, Thailand. After 2 days, we dequeened half of the colonies. Microsatellite genotyping showed that a queenless A. florea colony merged with a queenright A. florea colony, and a queenless A. andreniformis colony merged with a queenright A. florea colony. The inter-specific merger in particular shows that colonies can combine without direct kin benefits, and that colony mergers probably arise through strong queen attraction.     

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.     

Latitudinal gradients in colony size for social insects: termites and ants show different patterns

On the basis of a comparison of Nearctic and Neotropical ants, social insects have been proposed to show a latitudinal gradient in colony size. Further, the "fasting endurance hypothesis," which predicts larger colonies in areas with extended periods of low food availability, was proposed as the mechanism driving the gradient. To test the generality of the pattern and its mechanism, we examined the relationships between termite colony size and both latitude and annual evapotranspiration, a measure of plant productivity. We found no evidence that colony size increases with increasing latitude or decreasing plant productivity. We conclude that the pattern identified for ants cannot be generalized to include social insects as a whole. As is the case for ecogeographic gradients in insect body sizes, a pattern that is reported for one taxon may not be consistent for other taxa at the global level.     

Visual associative learning in restrained honey bees with intact antennae

A restrained honey bee can be trained to extend its proboscis in response to the pairing of an odor with a sucrose reward, a form of olfactory associative learning referred to as the proboscis extension response (PER). Although the ability of flying honey bees to respond to visual cues is well-established, associative visual learning in restrained honey bees has been challenging to demonstrate. Those few groups that have documented vision-based PER have reported that removing the antennae prior to training is a prerequisite for learning. Here we report, for a simple visual learning task, the first successful performance by restrained honey bees with intact antennae. Honey bee foragers were trained on a differential visual association task by pairing the presentation of a blue light with a sucrose reward and leaving the presentation of a green light unrewarded. A negative correlation was found between age of foragers and their performance in the visual PER task. Using the adaptations to the traditional PER task outlined here, future studies can exploit pharmacological and physiological techniques to explore the neural circuit basis of visual learning in the honey bee.     

Effects of social environment and worker mandibular glands on endocrine-mediated behavioral development in honey bees

Previous studies suggest that older honey bee workers possess an inhibitory signal that regulates behavioral development in younger bees. To study how this inhibitor is transmitted, bees were reared for 7 days in double-screen cages, single-screen cages, or unrestricted in a typical colony (control bees). Double-screen cages prevented physical contact with colony members while single-screen cages allowed only antennation and food exchange. Bees reared in double-screen cages showed accelerated endocrine and behavioral development; they had significantly higher rates of juvenile hormone biosynthesis and juvenile hormone titers than did control bees and also were more likely to become precocious foragers. Relative to the other two groups, bees reared in single-screen cages showed intermediate juvenile hormone biosynthesis rates and titers, and intermediate rates of behavioral development. These results indicate that physical contact is required for total inhibition. We also began to test the hypothesis that worker mandibular glands are the sources of an inhibitory signal. Old bees with mandibular glands removed were significantly less inhibitory towards young bees than were sham-operated and unoperated bees. These results suggest that an inhibitor is produced by the worker mandibular glands. Accepted: 29 January 1998     

An inclusive fitness model for the sex ratio in a partially sibmating population with inbreeding cost

Summary We construct an inclusive fitness model to find the evolutionarily stable sex ratios in a partially sibmating diploid or haplodiploid population. We assume a constant rate of sibmating with inbred offspring incurring a fitness penalty which, under haplodiploidy, is only suffered by females. We construct a one-locus genetic model for the same problem and observe that when selection is weak it gives the same numerical results as the inclusive fitness model.     

Multiple breeders, breeder shifts and inclusive fitness returns in an ant

In social insects, colonies may contain multiple reproductively active queens. This leads to potential conflicts over the apportionment of brood maternity, especially with respect to the production of reproductive offspring. We investigated reproductive partitioning in offspring females (gynes) and workers in the ant Formica fusca, and combined this information with data on the genetic returns gained by workers. Our results provide the first evidence that differential reproductive partitioning among breeders can enhance the inclusive fitness returns for sterile individuals that tend non-descendant offspring. Two aspects of reproductive partitioning contribute to this outcome. First, significantly fewer mother queens contribute to gyne (new reproductive females) than to worker brood, such that relatedness increases from worker to gyne brood. Second, and more importantly, adult workers were significantly more related to the reproductive brood raised by the colony, than to the contemporary worker brood. Thus, the observed breeder shift leads to genetic benefits for the adult workers that tend the brood. Our results also have repercussions for genetic population analyses. Given the observed pattern of reproductive partitioning, estimates of effective population size based on worker and gyne samples are not interchangeable.     

Monitoring circadian rhythms of individual honey bees in a social environment reveals social influences on postembryonic ontogeny of activity rhythms

Social factors constitute an important component of the environment of many animals and have a profound influence on their physiology and behavior. Studies of social influences on circadian rhythms have been hampered by a methodological trade-off: automatic data acquisition systems obtain high-quality data but are effective only for individually isolated animals and therefore compromise by requiring a context that may not be sociobiologically relevant. Human observers can monitor animal activity in complex social environments but are limited in the resolution and quality of data that can be gathered. The authors developed and validated a method for prolonged, automatic, high-quality monitoring of focal honey bees in a relatively complex social environment and with minimal illumination. The method can be adapted for studies on other animals. The authors show that the system provides a reliable estimation of the actual path of a focal bee, only rarely misses its location for > 1 min, and removes most nonspecific signals from the background. Using this system, the authors provide the first evidence of social influence on the ontogeny of activity rhythms. Young bees that were housed with old foragers show ~24-h rhythms in locomotor activity at a younger age and with stronger rhythms than bees housed with a similar number of young bees. By contrast, the maturation of the hypopharyngeal glands was slower in bees housed with foragers, similar to findings in previous studies. The morphology and function of the hypopharyngeal glands vary along with age-based division of labor. Therefore, these findings indicate that social inhibition of task-related maturation was effective in the experimental setup. This study suggests that although the ontogeny of circadian rhythms is typically correlated with the age-based division of labor, their social regulation is different.     

The influence of colony population and brood rearing intensity on the activity of detoxifying enzymes in worker honey bees

Abstract. Cohorts of worker honey bees from a single parental hive, cross-fostered into colonies which differed in population and other colony parameters, were assessed for activities of enzymes involved in metabolic detoxication. Activities of glutathione S-transferase and mixed-function oxidase enzymes were negatively correlated with foster colony population, but positively correlated with the ratio of larvae (brood)/adult workers. Worker bees which had begun foraging had enzyme activity levels higher than any found in bees which were still performing in-hive duties. Elevated levels of detoxifying enzymes in colonies with low populations and high ratios of larvae/adults may be a protective mechanism to prevent poisoning of larvae by toxins brought to the colony by foragers.     

Socialized medicine: Individual and communal disease barriers in honey bees

Honey bees are attacked by numerous parasites and pathogens toward which they present a variety of individual and group-level defenses. In this review, we briefly introduce the many pathogens and parasites afflicting honey bees, highlighting the biology of specific taxonomic groups mainly as they relate to virulence and possible defenses. Second, we describe physiological, immunological, and behavioral responses of individual bees toward pathogens and parasites. Third, bees also show behavioral mechanisms for reducing the disease risk of their nestmates. Accordingly, we discuss the dynamics of hygienic behavior and other group-level behaviors that can limit disease. Finally, we conclude with several avenues of research that seem especially promising for understanding host–parasite relationships in bees and for developing breeding or management strategies for enhancing honey bee health. We discuss how human efforts to maintain healthy colonies intersect with similar efforts by the bees, and how bee management and breeding protocols can affect disease traits in the short and long term.     

Wright-Fisher model of social insects with haploid males and diploid females

An inhomogeneous discrete Markov model is formulated for sexual random mating in finite populations of haploid male and diploid female individuals. This is a Wright-Fisher type of model for social insects. The generations are non-overlapping and of given finite sizes. Bottlenecks are included, allowing different sizes to change from generation to generation. Mutations and selection are included in this exact model for the stochastic process. Computations of the exact Markov model are presented, focussing on the sexually asymmetric genetic drift caused by haplodiploidy.