Worker policing persists in a hopelessly queenless honey bee colony (<Emphasis Type="Italic">Apis mellifera</Emphasis>)

Summary In queenright colonies of Apis mellifera, worker policing normally eliminates worker-laid eggs thereby preventing worker reproduction. However, in queenless colonies that have failed to rear a replacement queen, worker reproduction is normal. Worker policing is switched off, many workers have active ovaries and lay eggs, and the colony rears a last batch of male brood before dying out. Here we report a colony which, when hopelessly queenless, did not stop policing although a high proportion of workers had active ovaries (12.6%) and many eggs were laid. However, all these eggs and also worker-laid eggs transferred from another colony were policed. This unusual pattern was repeated eight weeks later by a second queenless colony made using worker bees from the same mother colony, which strongly suggests genetic determination.Received 19 May 2003; revised 11 September 2003; accepted 23 September 2003.     

Egg marking pheromones of anarchistic worker honeybees (Apis mellifera)

In honeybees, worker policing via egg eating enforces functionalworker sterility in colonies with a queen and brood. It is thoughtthat queens mark their eggs with a chemical signal, indicatingthat their eggs are queen-laid. Worker-laid eggs lack this signaland are, therefore, eaten by policing workers. Anarchistic workerhoneybees have been hypothesized to circumvent worker policingby mimicking the queen egg-marking signal. We investigated thisphenomenon by relating chemical profiles of workers and theireggs to egg acceptability. We found that the ability of someworkers (anarchistic workers in queenright colonies and deviantworkers from a queenless colony) to lay more acceptable eggsis due to them producing significant amounts of queen-like estersfrom their Dufour's gland. These esters appear to be transferredto eggs during laying and increase egg survival. However, theseesters cannot be the normal queen egg-marking signal, as theyare generally absent from queen-laid eggs and only increasethe short-term persistence of worker-laid eggs, because only7–30% of anarchistic worker-laid eggs persisted to hatchingversus 91–92% of queen-laid eggs. All workers can producesome esters, but only workers that greatly increase their esterproduction lay more acceptable eggs. The production of estersappears to be a flexible response, as anarchistic workers rearedin queenless colonies did not increase their ester production,while some deviant workers in queenless colonies did increasetheir ester production.     

Social parasitism by Cape honeybee workers in colonies of their own subspecies (Apis mellifera capensis Esch.)

Social parasitism is widespread in the eusocial insects. Although social parasites often show a reduced worker caste, unmated workers can also parasitize colonies. Cape honeybee workers, Apis mellifera capensis, can establish themselves as social parasites in host colonies of other honeybee subspecies. However, it is unknown whether social parasitism by laying workers also occurs among Cape honeybee colonies. In order to address this question we genotyped worker offspring of six queenless A. m. capensis colonies and determined the maternity of the reproducing workers. We found that three non-nestmate workers dominated reproduction in a host colony and produced 62.5% of the progeny. Our results show that social parasitism by laying workers is a naturally occurring part of the biology of Cape honeybees. However, such social parasitism is not frequently found (6.41% of the total worker offspring) probably due to co-evolutionary processes among A. m. capensis resulting in an equilibrium between selection for reproductive dominance in workers, colony maintenance and queen adaptation. Received 28 July 2005; revised 19 September and 11 November 2005; accepted 16 November 2005.     

Do policing honeybee (<Emphasis Type="Italic">Apis mellifera</Emphasis>) workers target eggs in drone comb?

Summary. Honey bee (Apis mellifera) workers police each other's reproduction by eating worker-laid eggs while preferentially leaving queen-laid eggs. Policing effort is presumably associated with biological costs, including those of search time and of errors of identification of eggs so that the wrong eggs are retained or eaten. Selection should act to minimise these costs. One way costs can be reduced is to focus policing effort on eggs that are most likely to be worker laid. We show here, in accordance with this prediction, that policing effort is focussed on drone cells where workers are more likely to lay eggs, rather than on worker cells which are more likely to contain queen-laid eggs.     

Worker policing in the German wasp Vespula germanica

In some ants, bees, and wasps, workers kill or "police" maleeggs laid by other workers in order to maintain the reproductiveprimacy of the queen. Kin selection theory predicts that multiplemating by the queen is one factor that can selectively favorworker policing. This is because when the queen is mated tomultiple males, workers are more closely related to the queen'ssons than to the sons of other workers. Earlier work has suggestedthat reproductive patterns in the German wasp Vespula germanicamay contradict this theory, because in some colonies a largefraction of the adult males were inferred to be the workers'sons, despite the effective queen mating frequency being greaterthan 2 (2.4). In the present study, we reexamine the V. germanicacase and show that it does support the theory. First, geneticanalysis confirms that the effective queen mating frequencyis high, 2.9, resulting in workers being more related to thequeen's sons than to other workers' sons. Second, behavioralassays show that worker-laid eggs are effectively killed byother workers, despite worker-laid eggs having the same intrinsicviability as queen-laid ones. Finally, we estimate that approximately58.4% of the male eggs but only 0.44% of the adult males areworker derived in queenright colonies, consistent with workerreproduction being effectively policed.     

Convergent evolution of worker policing by egg eating in the honeybee and common wasp

Mutual policing, where group members suppress each others' reproduction, is hypothesized to be important in the origin and stabilization of biological complexity. Mutual policing among workers in social insects can reduce within-colony conflict. However, there are few examples. We tested for worker policing in the common wasp Vespula vulgaris. Workers rapidly removed worker-laid eggs but left most queen-laid eggs (four out of 120 worker eggs versus 106 out of 120 queen eggs remained after 1h). Ovary dissection (1150 workers from six colonies) revealed that a small but significant number of workers have active ovaries (4%) equivalent to approximately five to 25 workers per colony. Consistent with effective policing of worker reproduction, microsatellite analysis of males (270 individuals from nine colonies) detected no workers' sons. Worker policing by egg eating has convergently evolved in the common wasp and the honeybee suggesting that worker policing may have broad significance in social evolution. Unlike the honeybee, relatedness patterns in V. vulgaris do not explain selection for policing. Genetic analysis (340 workers in 17 nests) revealed that workers are equally related to the queen's and other workers' sons (worker-worker relatedness was 0.51 +/- 0.04, 95% confidence interval). Worker policing in V. vulgaris may be selected due to the colony-level benefit of conflict suppression.     

Worker reproduction in the ant Formica fusca

We studied the kin conflict over male parentage in the ant Formica fusca. The conflict arises because each worker and queen is most related to her own sons and is thus predicted to lay eggs. Microsatellite analysis of eggs revealed that workers laid eggs in more than half the queenright experimental nests. Nevertheless, almost exclusively diploid offspring were reared in the presence of a queen. This also occurred when worker-laid haploid male eggs were experimentally introduced in to the nests. Because our experimental setup allowed us to exclude the possibility of queen policing, we conclude that worker laid eggs are removed by other workers, either as a response to their parentage or gender. Our results suggest that worker reproduction in F. fusca is ultimately an interplay of conflicts over male parentage and sex allocation and that both worker and self policing have roles as proximate mechanisms of resolution.     

The evolution of worker sterility in honeybees: the genetic basis of failure of worker policing

Worker honeybees (Apis mellifera) usually only lay eggs when their colony is queenless. However, an extremely rare ''anarchistic'' phenotype occurs, in which workers develop functional ovaries and lay large numbers of haploid eggs which develop into adult drones despite the presence of the queen. Studies of such colonies can give important insights into the mechanisms by which worker sterility is maintained in normal colonies. Here we report on the results of a breeding programme which enhanced the frequency of the anarchistic phenotype. Colonies derived from queens inseminated only by worker-laid males showed up to 9% of workers with highly developed ovaries. In these colonies a large proportion of males arose from worker-laid eggs. Colonies headed by queens inseminated with 50% worker-laid drones and 50% queen-laid drones showed variable phenotypes. In most such colonies there was no worker reproduction. In some, many workers had highly developed ovaries, but no worker-laid eggs were reared. In one colony, many worker-laid eggs were reared to maturity. The results suggest that the anarchy phenotype results from a complex interaction of queen genotype, the worker genotype of subfamilies that successfully reproduce and of those that do not, and the external environment.     

THE EVOLUTION OF WORKER STERILITY IN HONEY BEES: AN INVESTIGATION INTO A BEHAVIORAL MUTANT CAUSING FAILURE OF WORKER POLICING

Normally, worker honey bees (Apis mellifera) only lay eggs when their colony is queenless. When a queen is present, worker egg-laying is controlled by mutual “policing” behavior in which any rare worker-laid eggs are eaten by other workers. However, an extremely rare behavioral phenotype arises in which workers develop functional ovaries and lay large numbers of eggs despite the presence of the queen. In this study, microsatellite analysis was used to determine the maternity of drones produced in such a colony under various conditions. One subfamily was found to account for about 90% of drone progeny, with the remainder being laid by other subfamilies or the queen. No evidence of queen policing was found. After a one-month period of extreme worker oviposition in spring, the colony studied reverted to normal behavior and showed no signs of worker oviposition. However, upon removal of the queen, workers commenced oviposition very quickly. Significantly, the subfamily that laid eggs when the queen was present did not contribute to the drone production when the colony was queenless. However, another subfamily contributed a disproportionately large number of drones. The frequency of worker oviposition appears to be determined by opposing selective forces. Individual bees benefit from personal reproduction, whereas other bees and the colony are disadvantaged by it. Thus a behavioral polymorphism can be maintained in the population in which some workers can escape worker policing, with balancing selection at the colony level to detect and eliminate these mutations.     

Worker policing in the common wasp Vespula vulgaris is not aimed at improving colony hygiene

In insect societies, eggs laid by workers are frequently killed by other workers – a behaviour known as “worker policing”. The traditional explanation of worker policing is that it is a mechanism to resolve intracolony conflict, and maintain the reproductive monopoly of the queen. Recently, Pirk et al. (2004) proposed that worker policing instead is aimed at removing unviable worker-laid eggs and is ultimately just another example of hygienic behaviour. Here we test this hypothesis for the common wasp Vespula vulgaris, a species with highly effective worker policing. We show that worker-laid eggs from queenless colonies have a lower hatch rate (68%) than queen-laid eggs (82%). Analysis of egg laying rates of queens and workers, however, shows that the difference is not big enough to explain the apparent absence of adult worker-derived males in this species. Received 30 January 2006; revised 2 May 2006; accepted 5 May 2006.     

Egg discrimination by workers in <Emphasis Type="Italic">Diacamma</Emphasis> sp. from Japan

In eusocial Hymenoptera, workers usually cannot mate but can lay male-destined haploid eggs. In contrast, in many species, worker reproduction is regulated by means of worker policing, which consists of two behavioral categories: aggression towards workers that have developed ovaries, and the destruction of worker-laid eggs. We focused on the latter behavior in the ant Diacamma sp. from Japan, in which a mated worker (gamergate) serves as the functional queen in each colony. An experiment in which we introduced both worker-laid eggs and gamergate-laid eggs from foreign colonies showed that workers preferentially destroyed the worker-laid eggs. This indicates that workers can discriminate worker-laid eggs from gamergate-laid eggs. In contrast, gamergates destroyed all introduced eggs that they discovered. Our chemical analysis of egg surface substances revealed that the worker-laid eggs clearly differed from gamergate-laid eggs in their surface hydrocarbons (SHCs), with the former containing more long-chain components. However, a bioassay to test whether specific components of the SHCs trigger the observed discrimination behavior by workers remains to be done.     

Social parasitism by honeybee workers (Apis mellifera capensis Escholtz): host finding and resistance of hybrid host colonies

We studied possible host finding and resistance mechanisms ofhost colonies in the context of social parasitism by Cape honeybee(Apis mellifera capensis) workers. Workers often join neighboringcolonies by drifting, but long-range drifting (dispersal) tocolonies far away from the maternal nests also rarely occurs.We tested the impact of queenstate and taxon of mother andhost colonies on drifting and dispersing of workers and on the hosting of these workers in A. m. capensis, A. m. scutellata,and their natural hybrids. Workers were paint-marked accordingto colony and reintroduced into their queenright or queenlessmother colonies. After 10 days, 579 out of 12,034 labeled workerswere recaptured in foreign colonies. We found that driftingand dispersing represent different behaviors, which were differentlyaffected by taxon and queenstate of both mother and host colonies.Hybrid workers drifted more often than A. m. capensis and A.m. scutellata. However, A. m. capensis workers dispersed moreoften than A. m. scutellata and the hybrids combined, and A. m. scutellata workers also dispersed more frequently than thehybrids. Dispersers from queenright A. m. capensis colonieswere more often found in queenless host colonies and vice versa,indicating active host searching and/or a queenstate-discriminatingguarding mechanism. Our data show that A. m. capensis workersdisperse significantly more often than other races of A. mellifera,suggesting that dispersing represents a host finding mechanism.The lack of dispersal in hybrids and different hosting mechanismsof foreign workers by hybrid colonies may also be responsiblefor the stability of the natural hybrid zone between A. m.capensis and A. m. scutellata.     

A test of worker policing theory in an advanced eusocial wasp, Vespula rufa

Mutual policing is an important mechanism for maintaining social harmony in group-living organisms. In some ants, bees, and wasps, workers police male eggs laid by other workers in order to maintain the reproductive primacy of the queen. Kin selection theory predicts that multiple mating by the queen is one factor that can selectively favor worker policing. This is because when the queen is mated to multiple males, workers are more closely related to queen's sons than to the sons of other workers. Here we provide an additional test of worker policing theory in Vespinae wasps. We show that the yellowjacket Vespula rufa is characterized by low mating frequency, and that a significant percentage of the males are workers' sons. This supports theoretical predictions for paternities below 2, and contrasts with other Vespula species, in which paternities are higher and few or no adult males are worker produced, probably due to worker policing, which has been shown in one species, Vespula vulgaris. Behavioral observations support the hypothesis that V. rufa has much reduced worker policing compared to other Vespula. In addition, a significant proportion of worker-laid eggs were policed by the queen.     

Anarchy in the UK: Detailed genetic analysis of worker reproduction in a naturally occurring British anarchistic honeybee,Apis mellifera,colony using DNA microsatellites

Anarchistic behaviour is a very rare phenotype of honeybee colonies. In an anarchistic colony, many workers' sons are reared in the presence of the queen. Anarchy has previously been described in only two Australian colonies. Here we report on a first detailed genetic analysis of a British anarchistic colony. Male pupae were present in great abundance above the queen excluder, which was clearly indicative of extensive worker reproduction and is the hallmark of anarchy. Seventeen microsatellite loci were used to analyse these male pupae, allowing us to address whether all the males were indeed workers' sons, and how many worker patrilines and individual workers produced them. In the sample, 95 of 96 of the males were definitely workers' sons. Given that approximately 1% of workers' sons were genetically indistinguishable from queen's sons, this suggests that workers do not move any queen-laid eggs between the part of the colony where the queen is present to the area above the queen excluder which the queen cannot enter. The colony had 16 patrilines, with an effective number of patrilines of 9.85. The 75 males that could be assigned with certainty to a patriline came from 7 patrilines, with an effective number of 4.21. They were the offspring of at least 19 workers. This is in contrast to the two previously studied Australian naturally occurring anarchist colonies, in which most of the workers' sons were offspring of one patriline. The high number of patrilines producing males leads to a low mean relatedness between laying workers and males of the colony. We discuss the importance of studying such colonies in the understanding of worker policing and its evolution.     

Worker reproductive parasitism in naturally orphaned colonies of the Asian red dwarf honey bee, Apis florea

The truce between honey bee (Apis spp.) workers over reproduction is broken in the absence of their queen. Queenright workers generally abstain from personal reproduction, raising only the queen’s offspring. Queenless workers activate their ovaries, produce eggs, and reduce the rate at which they destroy worker-laid eggs, so that some eggs are reared to maturity. Reduced policing of worker-laid eggs renders queenless nests vulnerable to worker reproductive parasitism (WRP), and may result in the colony raising eggs of unrelated (non-natal) workers that parasitize it. Queenless colonies of A. florea are heavily parasitized with the eggs of non-natal workers. However, queenless colonies often abscond upon disturbance and build a small comb in which to rear their own male offspring. We investigated three naturally occurring orphaned colonies to determine if they are also parasitized. We show that WRP is present in orphaned colonies, and non-natal workers have significantly higher rates of ovary activation than natal workers. In contrast to experimentally manipulated colonies, in our samples, natal and non-natal workers had statistically equal reproductive success, but this may have been due to the small number of non-natals present.     

Specialization in policing behaviour among workers in the ant Pachycondyla inversa

Most animal societies are non-clonal and thus subject to conflicts. In social insects, conflict over male production can be resolved by worker policing, i.e. eating of worker-laid eggs (WLE) or aggression towards reproductive workers. All workers in a colony have an interest in policing behaviour being expressed, but there can be asymmetries among workers in performing the actual behaviour. Here, we show that workers of the ant Pachycondyla inversa specialize in policing behaviour. In two types of behavioural assays, workers developed their ovaries and laid eggs. In the first experiment, reproductive workers were introduced into queenright colonies. In the second experiment, WLE were introduced. By observing which individuals policed, we found that aggressive policing was highly skewed among workers that had opportunity to police, and that a similar tendency occurred in egg policing. None of the policing workers had active ovaries, so that policing did not incur a direct selfish benefit to the policer. This suggests that policing is subject to polyethism, just like other tasks in the colony. We discuss several hypotheses on the possible causes of this skew in policing tasks. This is the first non-primate example of specialization in policing tasks without direct selfish interests.     

A parent-of-origin effect on honeybee worker ovary size

Apis mellifera capensis is unique among honeybees in that unmated workers can produce pseudo-clonal female offspring via thelytokous parthenogenesis. Workers use this ability to compete among themselves and with their queen to be the mother of new queens. Males could therefore enhance their reproductive success by imprinting genes that enhance fertility in their daughter workers. This possibility sets the scene for intragenomic conflict between queens and drones over worker reproductive traits. Here, we show a strong parent-of-origin effect for ovary size (number of ovarioles) in reciprocal crosses between two honeybee subspecies, A. m. capensis and Apis mellifera scutellata. In this cross, workers with an A. m. capensis father had 30% more ovarioles than genotypically matched workers with an A. m. scutellata father. Other traits we measured (worker weight at emergence and the presence/absence of a spermatheca) are influenced more by rearing conditions than by parent-of-origin effects. Our study is the first to show a strong epigenetic (or, less likely, cytoplasmic maternal) effect for a reproductive trait in the honeybee and suggests that a search for parent-of-origin effects in other social insects may be fruitful.     

Honeybee workers use cues other than egg viability for policing

Worker policing, wherein social insect workers prevent their sisters from reproducing by eating worker-laid eggs, is recognized as a textbook example of kin selection in action. However, the evolutionary basis of policing was recently challenged in a study that suggested that police-workers remove worker-laid eggs not because rearing workers' sons reduces worker fitness, but merely because worker-laid eggs have low viability. Here, we refute Pirk et al.'s conclusions. First, we confirm earlier work that showed equal viability of eggs laid by queens and workers. Second, a statistical analysis of the data of Pirk et al. reveals that their own data do not support the conclusion that worker-laid eggs are policed merely because of their low viability. Third, we present data that unequivocally show that police-workers cannot discriminate between dead and live eggs. Hence, our study seriously weakens the challenge to the kin-selected basis of policing in honeybees.     

蜜蜂无政府主义蜂群的研究进展

西方蜜蜂Apis mellifera作为典型的社会性昆虫, 最重要的特征是生殖劳动分工。蜂王垄断蜂群的生殖权利, 工蜂生殖功能受到抑制, 从事除产卵和交配以外的所有职能。而在无政府主义蜂群中, 即使蜂王存在, 也有较多工蜂的卵巢激活并产卵, 蜂群中大多数雄蜂是工蜂的后代。这些特殊蜂群为正常蜂群工蜂不育机制研究提供了绝佳的反例材料。本文对无政府主义蜂群的行为特征、 产生条件、 遗传基础等研究进行了综述。无政府主义蜂群中有较多的工蜂产卵, 且工蜂所产卵能够逃避工蜂监督, 这种行为的产生受环境、 遗传组成、 基因表达等多种因素的影响, 并且遗传结构体系复杂, 参与调控的基因数量多。无政府主义蜂群行为机制的研究为工蜂不育机制的揭示及其他社会性昆虫工职不育基因的筛选和功能研究提供借鉴。     

Worker policing by egg eating in the ponerine ant Pachycondyla inversa

We investigated worker policing by egg eating in the ponerine ant Pachycondyla inversa, a species with morphologically distinct queens and workers. Colonies were split into one half with the queen and one half without. Workers in queenless colony fragments started laying unfertilized male eggs after three weeks. Worker-laid eggs and queen-laid eggs were introduced into five other queenright colonies with a single queen and three colonies with multiple queens, and their fate was observed for 30 min. Significantly more worker-laid eggs (range of 35-62%, mean of 46%) than queen-laid eggs (range of 5-31%, mean of 15%) were eaten by workers in single-queen colonies, and the same trend was seen in multiple-queen colonies. This seems to be the first well-documented study of ants with a distinct caste polymorphism to show that workers kill worker-laid eggs in preference to queen-laid eggs. Chemical analyses showed that the surfaces of queen-laid and worker-laid eggs have different chemical profiles as a result of different relative proportions of several hydrocarbons. Such differences might provide the information necessary for differential treatment of eggs. One particular alkane, 3,11-dimeC27, was significantly more abundant on the surfaces of queen-laid eggs. This substance is also the most abundant compound on the cuticles of egg layers.