Worker-laid Eggs Research Articles

Worker policing in the European hornet Vespa crabro

Although generally capable of producing males, workers in most hymenopteran societies (bees, ants and wasps) perform little or no reproduction in the presence of the queen. We investigated why workers do not reproduce in the European hornet Vespa crabro (L.). Previous genetic and behavioural work on this species had shown that, although queen mating frequency is low (effective paternity, 1.1) causing workers to be more related to workers' sons than to the queen's sons, workers do not lay eggs and the males reared are all the queen's sons. This suggested that workers are under queen pheromonal control. Here we show that this is not the case. Using egg introduction experiments, we show that worker policing behaviour occurs. We introduced queen-laid and worker-laid eggs into four discriminator colonies in five trials. In colonies with a queen, workers removed significantly more worker-laid than queen-laid eggs (1/79 worker-laid eggs but 46/72 queen-laid eggs remained after 16 h, p < 0.001). In colonies without a queen, workers removed significantly more queen-laid than worker laid eggs (30/44 worker-laid eggs but 13/41 queen-laid eggs remained after 16 h, p≤ 0.001). The presence of worker policing in queenright hornet colonies provides a proximate explanation for the absence of worker reproduction. Workers are not under queen control but instead are collectively enforcing their own sterility. Worker policing at low paternity may have been selected for because it enhances colony productivity by eliminating costly conflicts over reproduction.

Lack of worker reproduction in the giant honey bee Apis dorsata Fabricius

Worker policing (any behavior performed by workers that reduces reproduction by other workers) via egg eating has been observed in three species of honey bee (Apis mellifera, A. cerana, and A. florea). The maternity of drones of the giant honey bee A. dorsata (n = 660) was determined using DNA microsatellite analysis. None carried markers from the queen's mates indicating that none was a worker's son. In addition, dissection of 1,902 workers from 8 colonies showed that none had activated ovaries indicating that worker sterility is usual. Worker policing behavior involves costs when police workers make errors: removing eggs laid by a queen or failing to remove worker-laid eggs. We develop a model that examines the effect of these costs on the acceptance threshold of eggs. The model shows that costs may be reduced by any cues that help police workers distinguish worker-laid and queen-laid eggs. Once such cue may be the use of unique cells for rearing drones and workers. Unlike other Apis, A. dorsata rear both workers and drones in the same-size cells with the drone brood scattered among worker brood. Thus, the ability of A. dorsata workers to detect and eliminate (police) worker-laid eggs may be associated with higher costs than in other species. Our model suggests that these higher costs may select for a more permissive egg-acceptance threshold, because of the costs of erroneously removing queen-laid eggs, leading to greater worker reproduction. However our empirical results suggest that worker reproduction is very low in the species, suggesting that worker policing is efficient and that police workers have no difficulty in distinguishing queen-laid and worker-laid eggs.

Parasitic Cape honeybee workers, Apis mellifera capensis, evade policing.

Relocation of the Cape honeybee, Apis mellifera capensis, by bee-keepers from southern to northern South Africa in 1990 has caused widespread death of managed African honeybee, A. m. scutellata, colonies. Apis mellifera capensis worker bees are able to lay diploid, female eggs without mating by means of automictic thelytoky (meiosis followed by fusion of two meiotic products to restore egg diploidy), whereas workers of other honeybee subspecies are able to lay only haploid, male eggs. The A. m. capensis workers, which are parasitizing and killing A. m. scutellata colonies in northern South Africa, are the asexual offspring of a single, original worker in which the small amount of genetic variation observed is due to crossing over during meiosis (P. Kryger, personal communication). Here we elucidate two principal mechanisms underlying this parasitism. Parasitic A. m. capensis workers activate their ovaries in host colonies that have a queen present (queenright colonies), and they lay eggs that evade being killed by other workers (worker policing)-the normal fate of worker-laid eggs in colonies with a queen. This unique parasitism by workers is an instance in which a society is unable to control the selfish actions of its members.

Dufour's gland secretion of the queen honeybee ( Apis mellifera ): an egg discriminator pheromone or a queen signal?

The role of Dufour's gland secretion as an egg discriminator pheromone was reevaluated by simultaneously exposing workers to two combs, one containing queen- or worker-laid eggs and the second containing treated or untreated worker-laid eggs. Treatments included extracts of Dufour's gland secretion as well as the synthetic esters that were identified in the secretion. Policing was clearly detected both in queenright and queenless colonies by the swift removal of worker, but not of queen eggs. However, neither the glandular secretion nor its synthetic ester constituents were able to protect worker-born eggs from policing. Treated worker eggs were removed significantly faster than queen eggs, and at the same rate as non-treated worker eggs. These results are not consistent with the hypothesis that the secretion serves as an egg-marking pheromone. Chemical analyses of the queen abdominal tips revealed the presence of Dufour's esters, indicating that the glandular secretion oozes out and spreads over the cuticle around the genital chamber. However, contamination while ovipositing may also explain the minute amounts of these esters that were detected on the egg surface. Dufour's gland caste-specific composition suggests that in queens it may constitute a signal that plays a role in queen-worker interactions. Attraction bioassays revealed that the queen secretion, but not that of workers, is very attractive to workers. When applied either on a glass slide or on another worker, a retinue formed around the "surrogate queen". We conclude that Dufour's gland secretion constitutes part of a complex queen signal that is the basis for the social integrity of the honeybee colony.

Worker policing and worker reproduction in Apis cerana

Workers of the Asian hive bee, Apis cerana, are shown to have relatively high rates of worker ovary activation. In colonies with an active queen and brood nest, 1-5% of workers have eggs in their ovarioles. When A. cerana colonies are dequeened, workers rapidly activate their ovaries. After 4 days 15% have activated ovaries and after 6 days, 40%. A cerana police worker-laid eggs in the same way that A. florea and A. mellifera do, but are perhaps slightly more tolerant of worker-laid eggs than the other species. Nevertheless, no worker's sons were detected in a sample of 652 pupal males sampled from 4 queenright colonies. A cerana continue to police worker-laid eggs, even after worker oviposition has commenced in a queenless colony.

Policing in queenless ponerine ants

Potential reproductive conflicts are common in insect societies. One process that can reduce or suppress conflict is policing. We review worker and "queen" policing in queenless ponerine ants. Queenless ants are an important model system for the study of intracolony reproductive conflict. Policing is widespread in queenless ants because workers are totipotent, so that additional potential conflicts occur in comparison to species where workers cannot mate, and these additional conflicts are frequently reduced by policing. Policing is more diverse than suggested by the examples known in other social insects. In almost all species of social Hymenoptera it can include preventing workers from reproducing by killing worker-laid eggs, but in queenless ants it can additionally include immobilisation or mutilation of workers attempting to reproduce by replacing the gamergate (i.e. mated worker with a queen-like role) or by becoming an extra gamergate. Policing by both workers and by the gamergate are important. Policing can be facultative. Depending on the age of the gamergate, workers can prevent her replacement by immobilising challenging workers or they can favour replacement by immobilising the gamergate. The initial definition of policing was inspired by species in which workers retain ovaries but cannot mate. We broaden the definition to include species, such as queenless ants, where females are totipotent, thereby including not only conflict over male production but also over gamergate replacement and gamergate number. Finally, we compare policing with punishment and dominance hierarchy. Policing is not always punishment and it does not necessarily entail dominance relationships.

Worker policing in the bee Apis florea

Apis florea is a single-combed, open-nesting, dwarf honeybee indigenous to Asia. In common with other species of this genus, A. florea is highly polyandrous, and is therefore predicted to curtail worker reproduction by mutual policing mechanisms that keep worker reproduction at an extremely low level. Policing mechanisms could involve destruction of workers' eggs or offspring, or aggression toward those workers that are reproductively active. We show that in A. florea, worker-laid eggs are eliminated approximately twice as fast as queen-laid eggs, indicating that A. florea uses oophagy of worker-laid eggs as a mechanism of worker policing. Genetic analysis of four colonies indicated that all males produced were sons of queens, not workers. Dissections of 800 workers, from four colonies, did not reveal any significant levels of ovary activation. These results suggest that worker policing is an effective component of the mechanisms that maintain worker sterility in this species. Furthermore, they suggest that worker policing via oophagy of worker-laid eggs is pleisiomorphic for the genus.

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.

Evolution of worker sterility in honey-bees ( Apis mellifera) : how anarchistic workers evade policing by laying eggs that have low removal rates

In anarchistic honey-bee colonies, many workers’ sons are reared despite the presence of the queen. Worker-laid eggs are normally eaten by other workers in queenright colonies. Workers are thought to discriminate between queen-laid and worker-laid eggs by the presence or absence of a queen-produced egg-marking pheromone. This study compared the survival of three classes of eggs (worker-laid eggs from anarchistic colonies, worker-laid eggs from non-anarchistic queenless colonies, and queen-laid eggs) in both queenright normal colonies and queenright anarchistic colonies, in order to test the hypothesis that anarchistic workers evade policing by laying more acceptable eggs. As expected, few worker-laid eggs from non-anarchistic colonies survived more than 2 h. In contrast, worker-laid eggs from anarchistic colonies had much greater acceptability, which in some trials equalled the acceptability of queen-laid eggs. Anarchistic colonies were generally less discriminatory than normal queenright colonies towards worker-laid eggs, whether these originated from anarchistic colonies or normal queenless colonies. This indicates that the egg-removal aspect of the anarchistic syndrome involves both worker laying of eggs with greater acceptability and reduced discriminatory behaviour of policing workers.

Respiration rates in eggs of the honey bee, Apis mellifera

SUMMARYRespiration rates in queen-laid and worker-laid eggs of the honey bee, Apis mellifera, were determined for the 3days of embryonic development. Respiration was quantified by measuring the amount of CO2 produced during 13 h of artificial incubation at four temperature treatments: 28°C, 31°C, 34°C, 36°C (± 0.5°C). The mean respiration rates for fertilized and unfertilized eggs from queens were 140.3 ± 4.0 and 141.2 ± 12.2 nl CO2/h/egg, respectively. The mean respiration rate for unfertilized eggs from laying workers was 125.1 ± 6.3 nl CO2/h/egg. Mortality results, as indicated by pre-emergence embryos, showed that 75% developed at 34°C compared to 37.5% at 36°C. Low temperatures of 28°C and 31°C had 12.5% and 50% embryos developing to pre-emergence stage, respectively. Respiration results showed significant differences (P = 0.05) between the different days of incubation and temperature treatments, respectively. No significant difference was observed between the fertilized eggs and unfertilized eggs from queens at the same temperature treatment. The comparison of unfertilized eggs from queens and those from laying workers also showed no significant difference. When CO2 output on all the days and temperature treatments were compared, a significant regression (R2 = 0.645) was obtained (P = 0.05).

Development and behaviour of anarchistic honeybees

Anarchistic honeybees result from extremely rare behavioural mutations which allow workers to lay eggs despite the presence of the queen. We investigated the behavioural development of bees derived from a line in which ca. 5% of workers have developed ovaries and lay viable eggs. Other than their developed ovaries and proclivity to lay eggs, the anarchistic workers we studied are apparently normal, performing normal worker-like behaviour. Unlike many laying workers in queenless colonies, they are not queen-like and are apparently not the objects of aggression. When day-old workers from anarchistic colonies were cross-fostered into anarchistic and wild-type host colonies, the frequency of ovary development was an order of magnitude higher in the anarchistic host (9.1%) than in the wild-type host (0.7%). This suggests that there is a policing mechanism that affects ovary development in honeybees. Thus, worker reproduction is probably suppressed at the level of ovary development as well as by oophagy of worker-laid eggs. Other mechanisms, such as aggression towards individuals with developed ovaries, may also exist, but we found no evidence for this.

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.

Colony integration and reproductive conflict in honey bees

Honey bee colonies, although highly cooperative, are composed of genetically dis- tinct individuals with differing genetic payoffs from alternative allocations of colony resources among potential reproductive individuals. Therefore conflicts among colony members are expected. This paper analyzes the empirical evidence of these conflicts in sex ratio, nepotism in queen rearing, and worker production of males. Sex ratio conflict is expected to be minimal and hard to measure in honey bees, but behavioral studies might provide insights. Nepotism in queen rearing has been investigated by several studies. The weight of the evidence suggests that weak nepotism does occur. This paper provides a reanalysis of the data of one controversial study and compares the methods and results of others. Mixed negative and positive findings may be due to certain methodological differences, or to polymorphism for this trait. Worker laying is much more common than has long been thought, but nonetheless nearly all adult drones derive from the queen, because worker policing removes nearly all worker-laid eggs. Policing, both of eggs laid and worker ovary development, also may be responsible for complete sterility of most work- ers. Thus reproductive cooperation in honey bees is underlain by a low level of active conflict. © Inra/DIB/AGIB/Elsevier, Paris

Reproductive conflict in honey bees: a stalemate of worker egg-laying and policing

Using electrophoretic markers, eggs laid by workers were identified in honey bee (Apis mellifera) colonies with a queen. Based on extrapolation, these represented about 7% of the unfertilized (male) eggs laid in the colonies. A very small proportion of workers (of the order of 0.01%) lay these eggs. Worker-laid eggs are rapidly removed, so that very few sons of workers are reared. Thus the reproductive cooperation in bee colonies is maintained by ongoing antagonistic interactions among the members of the colony, with worker laying and egg removal policing by other workers being relatively common.

The effect of colony size on conflict over male-production between gamergate and dominant workers in the ponerine antDiacammasp.

Colonies of the queenless ponerine Diacamma sp. have females with three types of functions with respect to reproductive status: a mated worker (gamergate), egg-laying unmated dominant workers, and non-reproductive unmated subordinate workers. In the laboratory, several dominant workers oviposited but most eggs were eaten by the gamergate. However, some eggs, which may have resulted in the production of males, were overlooked and escaped from oophagy by the gamergate. The colony size of male-producing colonies was larger than that of nonmale producing colonies. An increasing difficulty for the gamergate to find worker-laid eggs caused by large colony size appears to be responsible for this phenomenon.

Evidence for a queen-produced egg-marking pheromone and its use in worker policing in the honey bee

SUMMARYWorker-laid and queen-laid male eggs were transferred into combs of empty drone cells in four honey bee (Apis mellifera ligustica) colonies. Worker-laid eggs treated with an ethanol extract of queen Dufour's gland were removed by workers (worker policing) at a significantly lower rate than either untreated or ethanol-treated worker-laid eggs, but this effect was less when a 1:10 dilution was used and it disappeared at a 1:100 dilution. Worker-laid eggs that had been touched to an area of a queen at the base of the sting and between the sting sheaths (‘sting- wipe’ treatment) were also removed at a significantly lower rate than untreated worker-laid control eggs. In all trials, the removal rate of worker-laid eggs exceeded that of queen-laid eggs. Queen-laid eggs treated with the polar solvents methanol and ethanol were removed more rapidly than those treated with the less-polar hexane and methylene chloride, but it was not possible to determine if this was because methanol and ethanol were more effective at removing a possible pheromone or because they caused more damage to the eggs. The results support a hypothesis that recognition of worker-laid eggs during worker policing is via a queen-produced egg-marking pheromone. Possible sources of pheromonal material besides the Dufour's gland are discussed.

Worker reproduction and related behavior in orphan colonies of a Japanese paper wasp,Polistes jadwigae (Hymenoptera, Vespidae)

Worker reproduction and related behavior in 2 orphan colonies ofPolistes jadwigae, one of which had been maintained by a queen and 5 artificially introduced alien workers, were observed. After the queen loss, a dominance hierarchy was established among workers, and several workers laid eggs without physical interference from other workers. Only males emerged from worker-laid eggs, however, a few new queens were produced from queen-laid eggs. Investment sex ratio of queenright (=normal) colonies (0.27) fell between the 2 theoretical values, corresponding to worker control (0.20 or 0.18) and queen control (0.48 or 0.46) of the sex ratio, both being calculated by considering the excess of males produced in the orphan colonies.

Worker policing in the honeybee

IN most species of social Hymenoptera with queen–worker dimorphism, workers cannot mate but retain functional ovaries1; because males arise from unfertilized haploid eggs, workers can potentially produce males. Worker-derived males are frequent in some species, but in others occur only in queenless colonies2,3. Workers are more related to their own sons (coefficient of 0.5) than to the queen's sons (their brothers; 0.25); they are also more related to nephews (0.375) than brothers if queens mate with one male, but if queens mate with more than two unrelated males a worker's mean rela tedness to nephews is less than to brothers3–5. In this case workers could benefit by 'worker policing'3,5: prevent-ing each other from producing males, perhaps by destroying worker-laid eggs or by aggression toward reproductive workers. Worker reproduction is rare in queenright colonies of species with multiply mated queens (such as honeybees6 and some yellowjacket wasps7), but is common in some monandrous species (bumblebees and stingless bees3). Here we describe experiments showing strong discrimination by honeybee (Apis mellifera) workers against worker-laid male eggs, supporting the worker-policing hypothesis. The honeybee was studied because queens mate with 10–20 males8, making worker policing seem likely as a cause for the rarity of worker-derived males (about one in a thousand males is worker-derived6).

Were Workers of Eusocial Hymenoptera Initially Altruistic or Oppressed?

Studies of a primitively eusocial halictid bee, Lasioglossum zephyrum, strongly suggest that a major factor in originating a worker caste is selection at the individual level for queens that control associated adult females. Even in this scarcely social form, the queen inhibits other adult females from becoming queens, perhaps by her high level of activity and frequent nudging in the nest. Queens are behaviorally less varied than workers and show specialization, particularly in frequency of nudging (which is concentrated on the worker with largest ovaries) and of backing. Backing draws workers, especially those with slender ovaries, down to lower parts of the burrows where the stimuli for cell construction and provisioning probably operate. Eating of worker-laid eggs by queens was also noted. In spite of the suggestion that queens have evolved to control their workers rather than that workers have evolved to help their queens, both may well have occurred, for these processes are not mutually exclusive; moreover, social attributes mutually beneficial to both castes no doubt have arisen.