Vibrational signals in the tremble dance of the honeybee,Apis mellifera

Summary The tremble dance is a behavior sometimes performed by honeybee foragers returning to the hive. The biological significance of this behavior was unclear until Seeley (1992) demonstrated that tremble dances occur mainly when a colony's nectar influx is so high that the foragers must undertake lenghty searches in order to find food storers to unload their nectar. He suggested that tremble dancing has the effect of stimulating additional bees to function as food-storers, thereby raising the colony's capacity for processing nectar. Here I describe vibrational signals emitted by the tremble dancers. Simulation experiments with artificial tremble dance sounds revealed that these sounds inhibited dancing and reduced recruitment to feeding sites. The results suggest that the tremble dance is a negative feedback system counterbalancing the positive feedback of recruitment by waggle dances. Thus, the tremble dance seems to affect not only the colony's nectar processing rate, but also its nectar intake rate.     

The causes of the tremble dance of the honeybee,Apis mellifera

Tremble dances are sometimes performed by returning forager bees instead of waggle dances. Recent studies by Seeley (1992) and Kirchner (1993) have revealed that this behaviour is part of the recruitment communication system of bees. The ultimate cause of tremble dances is, according to Seeley (1992), an imbalance between the nectar intake rate and the nectar processing capacity of the colony. This imbalance is correlated with a long initial search time of returning foragers to find bees to unload them. However, it remained unclear whether a long search time is the direct proximate cause of tremble dancing. Here we report that a variety of experimental conditions can elicit tremble dances. All of them have in common that the total search time that foragers spend searching for unloaders, until they are fully unloaded, is prolonged. This finding supports and extends the hypothesis that a long search time is the proximate cause of tremble dancing. The results also confirm the previous reports of Lindauer (1948) and others about factors eliciting tremble dancing.     

High degree of polyandry in Apis dorsata queens detected by DNA microsatellite variability

Workers of six colonies of the giant honeybee Apis dorsata from Sabah, Malaysia (five colonies) and Java (one colony) were genotyped using single locus DNA fingerprinting. The colonies from Sabah nested in colony aggregations of 5 and 28 nests respectively on two trees. Three DNA microsatellite loci (A14, A76, A88) with a total of 27 alleles provided sufficient genetic variability to classify the workers into distinct sub-families revealing the degree of polyandry of the queens. Queens mated on average with 30.17 ± 5.98 drones with a range from 19 to 53. The average effective number of matings per queen was 25.56 ± 11.63. In the total sample of 192 workers, 22 individuals were found that were not offspring of the colony's queen. Three of these were potentially drifted offspring workers from genotyped queens of colonies nesting on the same tree.     

Nest site selection in the open-nesting honeybee Apis florea

We studied nest site selection by swarms of the red dwarf honeybee, Apis florea. By video recording and decoding all dances of four swarms, we were able to determine the direction and distances indicated by 1,239 dances performed by the bees. The bees also performed a total of 715 nondirectional dances; dances that were so brief that no directional information could be extracted. Even though dances converged over time to a smaller number of areas, in none of the swarms did dances converge to one site. As a result, even prior to lift off, bees performed dances indicating nest sites in several different directions. Two of four swarms traveled directly in what seemed to be the general direction indicated by the majority of dances in the half hour prior to swarm lift off. The other two traveled along circuitous routes in the general direction indicated by the dances. We suggest that nest site selection in A. florea has similar elements to nest site selection in the better-studied Apis mellifera. However, the observation that many more locations are indicated by dances prior to lift off also shows that there are fundamental differences between the two species.     

Different policing rates of eggs laid by queenright and queenless anarchistic honey-bee workers (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.)

Worker-reproduction is rare in queenright honey-bee colonies. When workers do lay eggs, their eggs are normally eaten by other workers presumably because they lack the queen's egg-marking signal. Workers use the absence of this queen signal to enforce the queen's reproductive monopoly by policing any worker-laid eggs. In contrast, in anarchistic colonies, the majority of the males arise from worker-laid eggs. Anarchistic worker-laid eggs escape policing because workers perceive anarchistic eggs as queen-laid. However, in this study, we show that eggs laid by queenless anarchistic workers do not escape policing and have very similar removal rates to worker-laid eggs from queenless wild-type (i.e. non-anarchistic) colonies. This suggests that, under queenless conditions, eggs laid by anarchistic workers lose their chemical protection and are therefore no longer perceived as queen-laid. Hence, the egg-marking signal seems to be only applied to eggs when queen and brood are present. This suggests that in the absence of queen and brood, the biosynthetic pathway that produces the egg-marking signal is switched off.Communicated by L. Keller     

Role of esters in egg removal behaviour in honeybee (Apis mellifera) colonies

In queen-right honeybee colonies workers detect and eat the vast majority of worker-laid eggs, a behaviour known as worker policing. However, if a colony becomes permanently queen-less then up to 25% of the worker population develops their ovaries and lay eggs, which are normally reared into a final batch of males. Ovary development in workers is accompanied by changes in the chemical secretion of the Dufour's gland with the production of queen-like esters. We show that ester production increases with the period that the colony is queen-less. The increased ester production also corresponds to an increase in persistence of worker-laid eggs in queen-right colonies, since the esters somehow mask the eggs true identity. However, in a rare queen-less colony phenotype, workers always eat eggs indiscriminately. We found that the egg-laying workers in these colonies were unusual in that they were unable to produce esters. This apparently maladaptive egg eating behaviour is also seen in queen-less colonies prior to the appearance of egg-laying workers, a period when esters are also absent. However, the indiscriminate egg eating behaviour stops with the appearance of ester-producing egg-laying workers. These observations suggest that esters are providing some contextual information, which affects the egg eating behaviour of the workers.     

The reproductive dilemmas of queenless red dwarf honeybee (Apis florea) workers

Honeybee (Apis) workers cannot mate, but retain functional ovaries. When colonies have lost their queen, many young workers begin to activate their ovaries and lay eggs. Some of these eggs are reared, but most are not and are presumably eaten by other workers (worker policing). Here we explore some of the factors affecting the reproductive success of queenless workers of the red dwarf honeybee Apis florea. Over a 2-year period we collected 40 wild colonies and removed their queens. Only two colonies remained at their translocated site long enough to rear males to pupation while all the others absconded. Absconding usually occurred after worker policing had ceased, as evidenced by the appearance of larvae. Dissections of workers from eight colonies showed that in A. florea, 6% of workers have activated ovaries after 4 days of queenlessness, and that 33% of workers have activated ovaries after 3 weeks. Worker-laid eggs may appear in nests within 4 days and larvae soon after, but this is highly variable. As with Apis mellifera, we found evidence of unequal reproductive success among queenless workers of A. florea. In the two colonies that reared males to pupation and which we studied with microsatellites, some subfamilies had much higher proportions of workers with activated ovaries than others. The significance of absconding and internest reproductive parasitism to the alternative reproductive strategies of queenless A. florea workers is discussed.     

Differential feeding of worker larvae affects caste characters in the Cape honeybee,<Emphasis Type="Italic"> Apis mellifera capensis</Emphasis>

Sections of brood from colonies of the Cape honeybee ( Apis mellifera capensis), the African honeybee ( A. m. scutellata), and hybrid bees of the two races were exchanged between colonies to study the effect of different brood-origin/nurse-bee combinations on development of caste characters. When Cape larvae were raised by African workers the amount of food provided almost doubled in comparison with Cape larvae reared by their own workers. In contrast, African larvae raised by Cape workers were provided with only half the amount they received from their own workers. After the bees emerged, we found a large degree of plasticity in characters related to caste differentiation, which corresponded closely to the amount of food provided. Super-fed Cape bees had enlarged spermathecae, were heavier than normal workers and developed more rapidly, and had reduced pollen combs, all typical for a more queen-like condition. Ovariole numbers did not appear to be enhanced by additional feeding. Cape bees that behave as social parasites in African bee colonies were most queen-like in the characters studied, albeit within the range that was found for Cape bees from normal colonies, suggesting within-colony selection for characters that enhance reproduction.Communicated by R. Page     

Social parasitism by honeybee workers (Apis mellifera capensis Esch.): evidence for pheromonal resistance to host queen’s signals

Social parasites exploit their host’s communication system to usurp resources and reproduce. In the honeybee, Apis mellifera, worker reproduction is regulated by pheromones produced by the queen and the brood. Workers usually reproduce when the queen is removed and young brood is absent. However, Cape honeybee workers, Apis mellifera capensis, are facultative intraspecific social parasites and can take over reproduction from the host queen. Investigating the manner in which parasitic workers compete with host queens pheromonally can help us to understand how such parasitism can evolve and how reproductive division of labour is regulated. In A. m. capensis, worker reproduction is associated with the production of queen-like pheromones. Using pheromonal contest experiments, we show that Apis mellifera scutellata queens do not prevent the production of queen-like mandibular gland compounds by the parasites. Given the importance of these pheromones in acquiring reproductive status, our data suggest that the single invasive lineage of parasitic workers occurring in the range of A. m. scutellata was selected for its superior ability to produce these signals despite the presence of a queen. Such resistance was indeed less frequent amongst other potentially parasitic lineages. Resistance to reproductive regulation by host queens is probably the key factor that facilitates the evolution of social parasitism by A. m. capensis workers. It constitutes a mechanism that allows workers to evade reproductive division of labour and to follow an alternative reproductive option by acquiring direct fitness in foreign colonies instead of inclusive fitness in their natal nests.     

Coordinating a group departure: who produces the piping signals on honeybee swarms?

A swarm of honeybees provides a striking example of an animal group performing a synchronized departure for a new location; in this case, thousands of bees taking off at once to fly to a new home. However, the means by which this is achieved remain unclear. Shortly before takeoff, one hears a crescendo of a high-pitched mechanical signal—worker piping—so we explored the role of this signal in coordinating a swarm’s mass takeoff. Specifically, we examined whether exclusively nest site scouts produce the worker piping signal or whether it is produced in a relay or chain reaction fashion. We found no evidence that bees other than the scouts that have visited the swarm’s chosen nest site produce piping signals. This absence of relay communication in piping suggests that it is a signal that only primes swarms for takeoff and that the release of takeoff is triggered by some other signal or cue; perhaps the takeoff of bees on the swarm periphery as they reach flight temperature in response to piping.     

Potential mechanisms for the communication of height and distance by a stingless bee, Melipona panamica

This study investigates the recruitment communication mechanisms of a stingless bee, Melipona panamica, whose foragers can evidently communicate the three-dimensional location of a good food source. To determine if the bees communicate location information inside or outside the nest, we conducted removal experiments by training marked foragers to one of two identical feeders and then separating these experienced foragers from potential recruits as they left the nest. The feeders were positioned to test the communication of each dimension. The results show that recruits do not simply follow experienced foragers to the food source. Height and distance are communicated within the nest, while direction is communicated outside the nest. We then examined the pulsed sounds produced by recruiting foragers. While unloading food, recruiting foragers produced several short pulses and one or more very long pulses. On average, the longest unloading pulse per performance was 31–50% longer (P ≤ 0.018) for bees foraging on the forest floor than for bees foraging at the top of the forest canopy (40 m high). While dancing, recruiting foragers produced sound pulses whose duration was positively correlated with the distance to the food source (P < 0.001). Dancing recruiters also produced several short sound pulses followed by one or more long pulses. The longest dance pulse per performance was 291 ± 194 ms for a feeder 25 m from the nest and 1858 ± 923 ms for a feeder 360 m away from the nest. The mechanism of directional communication remains a mystery. However, the direction removal experiment demonstrates that newcomers cannot use forager-deposited scent marks for long-distance orientation (>100 m from the nest). Received: 25 September 1997 / Accepted after revision: 31 May 1998     

Nestmate recognition for eggs in the honeybee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.)

Colony integrity is fundamental to social insects and is threatened by the reproduction of non-nestmates. Therefore, discrimination between eggs derived from nestmates and non-nestmates would constitute an adaptation to prevent exploitation of the entire cooperative group by unrelated individuals. The removal of nestmate and non-nestmate queen and worker-laid eggs was evaluated in honeybees using colonies of Apis mellifera capensis to test female and of A. m. scutellata to test male eggs. The data show that honeybees can distinguish between nestmate and non-nestmate eggs of both sexes. Moreover, non-nestmate female queen-laid eggs were removed significantly faster than nestmate female worker-laid eggs in A. m. capensis, indicating that nestmate recognition cues can override caste-specific ones. While the experimental manipulation accounts for 37.2% (A. m. scutellata) or 1.6% (A. m. capensis) of variance in relation to egg removal, nestmate recognition explains 33.3% for male eggs (A. m. scutellata) and 60.6% for female eggs (A. m. capensis), which is almost twice as high as the impact of caste (16.7% A. m. scutellata; 25% A. m. capensis). Our data show a stronger effect of nestmate recognition on egg removal in the honeybee, suggesting that cues other than caste-specific ones (viability/kin) can dominate egg removal behavior. In light of intraspecific social parasitism, preventing the reproduction of unrelated individuals (group selection) rather than preferring queens’ eggs (kin selection) appears to be the driving force behind the evolution of egg removal behavior in honeybees.     

Self-organization of circadian rhythms in groups of honeybees (Apis mellifera L.)

Workers in social groups of honeybees (Apis mellifera L.) synchronize their individual free-running circadian rhythms to an overall group rhythm. By monitoring the activity of bees by recording the oxygen consumption and intragroup temperature, it is shown that the rhythm coordination is in part achieved by temperature fluctuations as an intragroup Zeitgeber. Trophallaxis was shown to have only a minor (if any) effect on circadian rhythm synchronization. A model incorporating a feed back loop between temperature and activity can plausibly explain the observed synchronization of individual rhythms in social groups as a self-organization phenomenon. Correspondence to: R.F.A. Moritz     

Differential reproductive success among subfamilies in queenless honeybee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.) colonies

With very rare exceptions, queenright worker honeybees (Apis mellifera L.) forego personal reproduction and suppress reproduction by other workers, preferring to rear the queens sons. This is in stark contrast to colonies that have lost their queen and have failed to rear a replacement. Under these conditions workers activate their ovaries and lay many eggs that develop parthenogenetically into a final brood of males (drones) before the colony perishes. Interestingly, not all workers contribute equally to this final generation of drones in queenless colonies. Some subfamilies (workers that share the same father) contribute a disproportionately greater number of offspring than other subfamilies. Here we explore some of the mechanisms behind this reproductive competition among subfamilies. We determined the relative contribution of different subfamilies present in colonies to laying workers, eggs, larvae and pupae by genotyping samples of all life stages using a total of eight microsatellite loci. Our colonies were headed by free-mated queens and comprised 8–17 subfamilies and therefore differed significantly from colonies used in an earlier study investigating the same phenomena where colonies comprised an artificially low number of subfamilies. We show that, first, subfamilies vary in the speed with which they activate their ovaries after queen-loss and, second, that the survival of eggs to the larval stage is unequal among subfamilies suggesting that some subfamilies lay eggs that are more acceptable than others. However, there is no statistically significant difference among subfamilies in the survival of larvae to pupae, indicating that ovary activation and egg survival are the critical components to reproductive competition among subfamilies of queenless honeybee workers.Communicated by R. Page     

Propagation of olfactory information within the honeybee hive

Transfer of information about food source characteristics within insect societies is essential to colony-foraging success. The food odor communicated within honeybee hives has been shown to be important for food source exploitation. When successful foragers return to the nest and transfer the collected nectar to hive mates through mouth-to-mouth contacts (trophallaxis), potential recruits receiving these samples learn the food odor by associative learning. The food then becomes rapidly distributed among colony members, which is mainly a consequence of the numerous trophallaxes between hive-mates of all ages during food processing. We tested whether the distribution of food among hive mates causes a propagation of olfactory information within the hive. Using the proboscis extension response paradigm, we show that large proportions of bees of the age groups representing the main worker castes, 4 to 9-day-old bees (nurse-aged bees), 12 to 16-day-old bees (food processor-aged bees), and actual foragers (about 17+ day old bees) associatively learn the food odor in the course of processing food that has been collected by only a few foragers. Results further suggest that the information is shared more or less equally between bees of the three age groups. This shows that olfactory information about the flower species exploited by foragers is distributed within the entire colony and is acquired by bees of all age groups, which may influence many behaviors inside and outside the hive.     

Net energetic advantage drives honey bees (Apis mellifera L) to nectar larceny in Vaccinium ashei Reade

Carpenter bees (Xylocopa spp.) act as primary nectar thieves in rabbiteye blueberry (Vaccinium ashei Reade), piercing corollas laterally to imbibe nectar at basal nectaries. Honey bees (Apis mellifera L) learn to visit these perforations and thus become secondary nectar thieves. We tested the hypothesis that honey bees make this behavioral switch in response to an energetic advantage realized by nectar-robbing flower visits. Nectar volume and sugar quantity were higher in intact than perforated flowers, but bees (robbers) visiting perforated flowers were able to extract a higher percentage of available nectar and sugar so that absolute amount of sugar (mg) removed by one bee visit is the same for each flower type. However, because perforated flowers facilitate higher rates of bee flower visitation and the same or higher rates of nectar ingestion, they are rendered more profitable than intact flowers in temporal terms. Accordingly, net energy (J) gain per second flower handling time was higher for robbers on most days sampled. We conclude that the majority evidence indicates an energetic advantage for honey bees that engage in secondary nectar thievery in V. ashei.Communicated by R. Page     

The functional organization of resin work in honeybee colonies

Resin is an important building material in the nests of honeybees, but little is known about how it is handled within the nest and how its collection is controlled. We studied the functional organization of resin work to better understand how a colony adaptively controls its intake of resin. Two hypotheses have been proposed for how resin collectors stay informed of the need for additional resin: (1) the unloading difficulty hypothesis (resin need is sensed indirectly by the unloading delay) and (2) the caulking activity hypothesis (resin need is sensed directly while engaged in using resin). A falsifiable prediction of the latter hypothesis, but not of the former, is that resin collectors not only gather resin outside the hive but also regularly handle resin inside the hive (taking it from other bees and using it to caulk crevices). Consistent with this prediction are our findings that in the resin sector of a colony’s economy, unlike in the pollen, nectar, and water sectors, there is no strict division of labor between the collectors and the users of a material. Over the course of a day, bees seen collecting resin were also commonly seen using resin. Moreover, we found that the unloading locations of resin collectors are unlike those of water and nectar collectors, being deep inside the hive (at the sites of resin use) rather than at the hive entrance. This arrangement facilitates the engagement in resin use by resin collectors. We conclude that the caulking activity hypothesis is well-supported, but that the unloading difficulty hypothesis also remains viable, for we found that resin collectors experience variable delays in getting rid of their loads, from less than 15 min to more than an hour, consistent with this hypothesis. The stage is now set for experimental tests of these two hypotheses. Both may be correct, which if true will imply that social insect workers, despite their small brains, can acquire and integrate information from multiple sources to improve their knowledge of conditions within the colony.     

Levels of polyandry and intracolonial genetic relationships in Apis florea

DNA was extracted from worker and drone pupae of each of five colonies of the dwarf honey bee Apis florea. Polymerase chain reactions (PCR) were conducted on DNA extracts using five sets of primers known to amplify microsatellite loci in A. mellifera. Based on microsatellite allele distributions, queens of the five colonies mated with at least 5–14 drones. This is up to 3 times previous maximum estimates obtained from sperm counts. The discrepancy between sperm count and microsatellite estimates of the number of matings in A. florea suggests that despite direct injection of semen into the spermatheacal duct, either A. florea drones inject only a small proportion of their semen, or queens are able to rapidly expel excess semen after mating. A model of sexual selection (first proposed by Koeniger and Koeniger) is discussed in which males attempt to gain reproductive dominance by increasing ejaculate volume and direct injection of spermatozoa into the spermatheca, while queens attempt to maintain polyandry by retaining only a small fraction of each male's ejaculate. It is shown, at least in this limited sample, that the effective number of matings is lower in A. florea than in A. mellifera.     

Generalist cuckoo bees (Hymenoptera: Apoidea: Sphecodes) are species-specialist at the individual level

Intensive and incessant arms races between a parasite and its host are generally expected to lead to parasite specialization. Nevertheless, some parasitic species still successfully attack wide spectra of hosts. One of the solutions to the evolutionary enigma of the long-term existence of generalist parasites is their specialization at an individual level, a phenomenon well known, e.g., in European common cuckoo. Over its range, it parasitizes a number of bird species; however, individual females are mostly specialists possessing adaptations to a particular host species. In this study, we test the possibility of individual specialization in generalist cuckoo bees, the insect counterparts of avian cuckoos. Females of cuckoo bees lay each egg into a single brood cell in the nests of other bee species. The host’s offspring is destroyed by the parasitic female or later by her larvae, which feed on pollen supplies accumulated by the host. Both studied cleptoparasitic bees (Sphecodes ephippius and Sphecodes monilicornis) are widely distributed in Europe, where they have been reported to use broad host spectra. We recorded several host species (including some previously unknown) for both cuckoo bee species, and confirmed that these parasites are indeed generalist even at a small local scale. However, we demonstrate that exactly as in the avian cuckoos, each female in both species of generalist bee parasites tends to attack just one host species.