Honey bee hygienic behaviour does not incur a cost via removal of healthy brood.

In the honey bee, hygienic behaviour, the removal of dead or diseased brood from capped cells by workers, is a heritable trait that confers colony-level resistance against brood diseases. This behaviour is quite rare. Only c. 10% of unselected colonies show high levels of hygiene. Previous studies suggested that hygiene might be rare because it also results in the removal of healthy brood, thereby imposing an ongoing cost even when brood diseases are absent. We tested this hypothesis by quantifying hygienic behaviour in 10 colonies using a standard technique, the freeze-killed brood (FKB) bioassay. At the same time, we also quantified the removal of untreated brood. The study colonies showed a wide range in hygienic behaviour, removing 19.7-100% of the FKB. The removal of untreated brood ranged from 2% to 44.4%. However, there was no correlation between the two removal rates for any of the four age groups of untreated brood studied (eggs, young larvae, older larvae from uncapped cells and larvae/pupae from capped cells). These results do not support the cost-to-healthy-brood hypothesis for the rarity of hygienic behaviour.

The natural history of nest defence in a stingless bee, Tetragonisca angustula (Latreille) (Hymenoptera: Apidae), with two distinct types of entrance guards.

The stingless bee Tetragonsica angustula (Latreille) is the only social bee known that has two different types of nest entrance guards. As in other stingless bees and the honey bee one type stands on, in or near the nest entrance. The second type, so far only known in T. angustula, hovers near the nest entrance. In order to gain further understanding of this unique situation we studied guarding behaviour in both types of guards. Using marked bees, we found that individual worker bees guarded for a long time, up to 20 days, relative to their short, average c. 21 day, lifespan. Relatively few, 33%, individually marked guards were seen performing both types of guarding. The others only acted as standing guards. The bees that did perform both types did so over similar periods of their life. Hovering bouts were 57 min long, interrupted by breaks inside the hive of a few minutes (3.3 ± 1.5 min). Standing bouts were slightly longer (74 min) and also interrupted by short breaks (7.82 ± 6.45 min). Human breath, mimicking a vertebrate intruder, caused the guards to retreat into the nest rather than to attack the intruder. Some colonies protected themselves against intruders by closing the entrance during the night (32% and 56% of colonies during two nights). In summary, our results indicate that nest entrance guarding in T. angustula involves division of labour between the two types, in which most guarding individuals only act as standing guards.

Hygienic behavior in the stingless bees Melipona beecheii and Scaptotrigona pectoralis (Hymenoptera: Meliponini).

Hygienic behavior, a trait that may confer resistance to brood diseases in the honey bee Apis mellifera, was studied in two species of stingless bees in Mexico. Eight colonies each of Melipona beecheii and Scaptotrigona pectoralis were tested for hygienic behavior, the removal of dead or diseased brood, by freeze killing a comb of sealed cells containing pupae. Both species detected and removed dead brood. However, removal rates differed between species. In M. beecheii colonies, workers took 2-9 days to remove 100% of the dead brood (4.4 +/- 2.0 days, mean +/- SD), while S. pectoralis removed all dead brood in less than 3 days (2.3 +/- 0.6 days, mean +/- SD). We conclude that hygienic behavior is not unique to A. mellifera, and is not solely an adaptation for the reuse of brood cells as occurs in honey bees but not stingless bees. Although stingless bees do not reuse brood cells, space is limited. The removal of dead brood may be necessary to allow new cells to be constructed in the same place.

Multi-level selection for hygienic behaviour in honeybees.

Disease is one of the main factors driving both natural and artificial selection. It is a particularly important and increasing threat to the managed honeybee colonies, which are vital in crop pollination. Artificial selection for disease-resistant honeybee genotypes has previously only been carried out at the colony-level, that is, by using queens or males reared from colonies that show resistance. However, honeybee queens mate with many males and so each colony consists of multiple patrilines that will vary in heritable traits, such as disease resistance. Here, we investigate whether response to artificial selection for a key resistance mechanism, hygienic behaviour, can be improved using multi-level selection, that is, by selecting not only among colonies as normal but also among patrilines within colonies. Highly hygienic colonies were identified (between-colony selection), and the specific patrilines within them responsible for most hygienic behaviour were determined using observation hives. Queens reared from these hygienic patrilines (within-colony selection) were identified using DNA microsatellite analysis of a wing-tip tissue sample and then mated to drones from a third highly hygienic colony. The resulting colonies headed by queens from hygienic patrilines showed approximately double the level of hygienic behaviour of colonies headed by sister queens from non-hygienic patrilines. The results show that multi-level selection can significantly improve the success of honeybee breeding programs.

Multiple paternity or multiple queens: two routes to greater intracolonial genetic diversity in the eusocial Hymenoptera.

Understanding the evolution of multiple mating by females (polyandry) is an important question in behavioural ecology. Most leading explanations for polyandry by social insect queens are based upon a postulated fitness benefit from increased intracolonial genetic diversity, which also arises when colonies are headed by multiple queens (polygyny). An indirect test of the genetic diversity hypotheses is therefore provided by the relationship between polyandry and polygyny across species, which should be negative if the genetic diversity hypotheses are correct. Here, we conduct a powerful comparative investigation of the relationship between polyandry and polygyny for 241 species of eusocial Hymenoptera (ants, bees and wasps). We find a clear and significant negative relationship between polyandry and polygyny after controlling for phylogeny. These results strongly suggest that fitness benefits resulting from increased intracolonial genetic diversity have played an important role in the evolution of polyandry, and possibly polygyny, in social insects.

Comparative study in stingless bees (Meliponini) demonstrates that nest entrance size predicts traffic and defensivity.

Stingless bees (Meliponini) construct their own species-specific nest entrance. The size of this entrance is under conflicting selective pressures. Smaller entrances are easier to defend; however, a larger entrance accommodates heavier forager traffic. Using a comparative approach with 26 species of stingless bees, we show that species with greater foraging traffic have significantly larger entrances. Such a strong correlation between relative entrance area and traffic across the different species strongly suggests a trade-off between traffic and security. Additionally, we report on a significant trend for higher forager traffic to be associated with more guards and for those guards to be more aggressive. Finally, we discuss the nest entrance of Partamona, known in Brazil as boca de sapo, or toad mouth, which has a wide outer entrance but a narrow inner entrance. This extraordinary design allows these bees to finesse the defensivity/traffic trade-off.

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.

Crossing the taxonomic divide: conflict and its resolution in societies of reproductively totipotent individuals.

Reproduction in groups may be unequal, with one or a few individuals monopolizing direct reproduction assisted by nonbreeding helpers. In social insects this has frequently led to a pronounced queen-worker dichotomy and a loss of reproductive totipotency among workers. However, in some invertebrate and all vertebrate societies, all or most individuals remain reproductively totipotent. In these groups, conflicts of interest over reproduction are potentially greatest. Here, we synthesize previous analyses of reproductive conflict, aggression and breeder replacement in haplodiploid societies of totipotent individuals and extend them to cover diploid (vertebrate) examples. We test predictions arising from this approach using the best-studied invertebrate (Dinoponera queenless ants) and vertebrate (naked mole-rat, Heterocephalus glaber) examples, although in principle our analysis applies to all similar groups. We find that premature replacement of a parent breeder by nonbreeders (overthrow) is rare. Dominant coercive control of nonbreeders by the breeder is often unnecessary and honest signalling of breeder vitality can maintain group stability and resolve conflicts over reproduction. We hope that by providing an explicit transfer of social theory between ants and naked mole-rats we will stimulate further cross-taxonomic studies that will greatly broaden our understanding of sociality.

Worker reproduction and policing in insect societies: an ESS analysis.

Insect societies are vulnerable to exploitation by workers who reproduce selfishly rather than help to rear the queen's offspring. In most species, however, only a small proportion of the workers reproduce. Here, we develop an evolutionarily stable strategy (ESS) model to investigate factors that could explain these observed low levels of reproductive exploitation. Two key factors are identified: relatedness and policing. Relatedness affects the ESS proportion of reproductive workers because laying workers generally work less, leading to greater inclusive fitness costs when within-colony relatedness is higher. The second key factor is policing. In many species, worker-laid eggs are selectively removed or 'policed' by other workers or the queen. We show that policing not only prevents the rearing of worker-laid eggs but can also make it unprofitable for workers to lay eggs in the first place. This can explain why almost no workers reproduce in species with efficient policing, such as honeybees, Apis, and the common wasp, Vespula vulgaris, despite relatively low relatedness caused by multiple mating of the mother queen. Although our analyses focus on social insects, the conclusion that both relatedness and policing can reduce the incentive for cheating applies to other biological systems as well.

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.

Magnetic resonance imaging in entomology: a critical review.

Magnetic resonance imaging (MRI) enables in vivo imaging of organisms. The recent development of the magnetic resonance microscope (MRM) has enabled organisms within the size range of many insects to be imaged. Here, we introduce the principles of MRI and MRM and review their use in entomology. We show that MRM has been successfully applied in studies of parasitology, development, metabolism, biomagnetism and morphology, and the advantages and disadvantages relative to other imaging techniques are discussed. In addition, we illustrate the images that can be obtained using MRM. We conclude that although MRM has significant potential, further improvements to the technique are still desirable if it is to become a mainstream imaging technology in entomology.

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.