Vibration Signal Behavior of Waggle-dancers in Swarms of the Honey Bee,Apis mellifera (Hymenoptera: Apidae)

We hypothesize two functions of the vibration signal (dorsal ventral abdominal vibration = DVAV) during swarming in honey bees: 1. it enhances recruitment to the specific sites advertised by the waggle dancers which also perform the vibration signal; and 2. it acts as a nonspecific modulatory signal to stimulate activity in other bees. The stimulation of activity invoked by the second hypothesis might include increasing nest-site scouting and dance following early in the house-hunting process or rousing quiescent bees to prepare them for lift-off late in the process, or both. In studies of neotropical African bee swarms in Costa Rica and European bees in California we tested these hypotheses by looking for associations between production of vibration signals by nest-site recruiters and site attractiveness (indicated by which site was ultimately chosen and by distance from the swarm since swarms may have a distance preference). Overall, bees dancing for the chosen sites performed vibration signals to the same extent as those dancing for the other sites. There were no distance differences between sites whose scouts did and did not vibrate other bees. These results are inconsistent with the hypothesis that the vibration signal enhances recruitment to especially high quality sites and they support the hypothesis that it plays a general excitatory role in the context of house hunting by swarming bees.     

Nest‐Site Defense by Competing Honey Bee Swarms During House‐Hunting

Cavity‐nesting animals must often defend their homes against intruders, especially when the availability of suitable cavities is limited. Competition for nest sites is particularly strong when multiple groups of the same species migrate synchronously to found a new home. This may be the case for honey bees during the reproductive season, because neighboring colonies often cast swarms simultaneously, leading to potential competition for high‐quality nesting cavities. To test the idea that honey bee swarms may compete for and defend potential nest sites as they search for a new home, we observed pairs of artificial swarms that were house‐hunting concurrently. Workers from one swarm in each pair carried a gene influencing body color, so that the bees from the two swarms were easily distinguished. We set up a high‐quality nest box and waited for nest‐site scouts from each swarm to explore and recruit swarm mates to it. We recorded all the interactions between competing scouts at the nest box and found that when scouts from both swarms explored the box simultaneously they behaved agonistically toward bees from the other swarm. The level of aggression depended on the number of scouts from each swarm present at the nest box. When only one to three scouts from each swarm were at the box, they rarely fought. But when the scouts from one swarm outnumbered those from the other swarm (4–20 vs. one to three bees), those in the majority advertised their presence with a buzzing behavior at the entrance opening, and started mobbing and killing those in the minority. When one swarm gained clear control of the nest box (20+ vs. zero to one bees), some of its scouts guarded the box’s entrance, preventing entry by foreign scouts. Our study exemplifies how cavity‐nesting animals may compete for and defend suitable nesting sites.     

Searching for a new home--scouting behavior of honeybee swarms

Honeybee scouting, where individual bees search the environmentwithout prior information about the possible location of foodsources or nest sites, is notoriously difficult to study. Yet,understanding scouting behavior is important as it providesinsights into how social insects trade-off exploitation withexploration. The use of simulation models is an ideal way toinvestigate the possible mechanisms behind the regulation ofscouting at the group level as well as the ways in which theswarm searches its environment. We used an individual-basedsimulation model to study the scouting behavior of honeybeeswarms. In our model, we implemented a simple decision rulethat regulates the number of scouts: individual bees first attemptto find a dance to follow but become scouts if they fail todo so. We show that this rule neatly allows the swarm to adjustthe number of scouts depending on the quality of the nest sitesknown to the swarm. We further explored different search strategiesthat allow the swarm to select good-quality nest sites independentof their distance from the swarm. Assuming that it is costlyto move to a site that is far away, the best search strategywould be to give precedence to nearby sites while still allowingthe discovery of better sites at distances farther away.     

Vibration Signal Modulates the Behavior of House-hunting Honey Bees (Apis mellifera)

Honey bees ( Apis mellifera ) in house-hunting swarms perform vibration signals (dorsoventral abdominal vibration (DVAV)) of 18.05 ± 0.45 Hz for 1.36 ± 0.23 s throughout the house selection process. These signals are performed by a specialized subset of bees, most of whom never perform recruitment dances to nest sites. Individuals repeatedly vibrate others. The patterns of vibration signal performance are consistent with the hypothesis that it serves to activate bees for take-off, but may also activate bees to scout for nest sites.     

The Use of the Vibration Signal and Worker Piping to Influence Queen Behavior during Swarming in Honey Bees, Apis mellifera

We investigated worker regulation of queen activity during reproductive swarming by examining the rates at which workers performed vibration signals and piping on queens during the different stages of the swarming process. Worker–queen interactions were first examined inside observation hives during the 2–3 wk that preceded the issue of the swarm (pre‐swarming period) and then inside the swarm clusters during the period that preceded liftoff and relocation to a new nest site (post‐swarming period). Queen court size did not differ between the pre‐ and post‐swarming periods, but workers fed the queens less inside the swarm clusters. Workers performed vibration signals on the queens at increasing rates throughout the pre‐swarming period inside the natal nest, but rarely or never vibrated the queen inside the swarm. Piping was performed on the queens during both the pre‐ and post‐swarming periods and always reached a peak immediately before queen flight. During the final 2–4 h before swarm liftoff, queens were increasingly contacted by waggle dancers for nest sites, some of which piped the queen. The vibration signal may operate in a modulatory manner to gradually prepare the queen for flight from the natal nest, and the cumulative effects of the signal during the pre‐swarming period may make further vibrations on the queen unnecessary when inside the swarm cluster. In contrast, worker piping may function in a more immediate manner to trigger queen takeoff during both the pre‐ and post‐swarming periods. Workers that vibrate and pipe the queen tend to be older, foraging‐age bees. The regulation of queen activity during colony reproduction may therefore be controlled largely by workers that normally have little contact with queens, but help to formulate colony reproductive and movement decisions.     

Worker piping in honey bee swarms and its role in preparing for liftoff

Worker piping, previously reported only in hives, was observed in swarms as they prepared to liftoff to fly to a new home. Pipers are excited bees which scramble through the swarm cluster, pausing every second or so to emit a pipe. Each pipe consists of a sound pulse which lasts 0.82 +/- 0.43 s and rises in fundamental frequency from 100-200 Hz to 200-250 Hz. Many. if not all, of the pipers are nest-site scouts. The scouts pipe when it is time to stimulate the non-scouts to warm themselves to a flight-ready temperature (35 degrees C) in preparation for liftoff. The time-course of worker piping matches that of swarm warming, both start at a low level, about an hour before liftoff, and both build to a climax at liftoff. When we excluded pipers from bees hanging in the cool, outermost layer of a swarm cluster, we found that these bees did not warm up. The form of worker piping that we have studied in swarms differs from the form of worker piping that others have studied in hives. We call the two forms "wings-together piping" (in swarms) and "wings-apart piping" (in hives).     

Information flow,opinion polling and collective intelligence in house-hunting social insects

The sharing and collective processing of information by certain insect societies is one of the reasons that they warrant the superlative epithet ''super-organisms'' (Franks 1989, Am. Sci. 77, 138-145). We describe a detailed experimental and mathematical analysis of information exchange and decision-making in, arguably, the most difficult collective choices that social insects face: namely, house hunting by complete societies. The key issue is how can a complete colony select the single best nest-site among several alternatives? Individual scouts respond to the diverse information they have personally obtained about the quality of a potential nest-site by producing a recruitment signal. The colony then deliberates over (i.e. integrates) different incoming recruitment signals associated with different potential nest-sites to achieve a well-informed collective decision. We compare this process in honeybees and in the ant Leptothorax albipennis. Notwithstanding many differences - for example, honeybee colonies have 100 times more individuals than L. albipennis colonies - there are certain similarities in the fundamental algorithms these societies appear to employ when they are house hunting. Scout honeybees use the full power of the waggle dance to inform their nest-mates about the distance and direction of a potential nest-site (and they indicate the quality of a nest-site indirectly through the vigour of their dance), and yet individual bees perhaps only rarely make direct comparisons of such sites. By contrast, scouts from L. albipennis colonies often compare nest-sites, but they cannot directly inform one another of their estimation of the quality of a potential site. Instead, they discriminate between sites by initiating recruitment sooner to better ones. Nevertheless, both species do make use of forms of opinion polling. For example, scout bees that have formerly danced for a certain site cease such advertising and monitor the dances of others at random. That is, they act without prejudice. They neither favour nor disdain dancers that advocate the site they had formerly advertised or the alternatives. Thus, in general the bees are less well informed than they would be if they systematically monitored dances for alternative sites rather than spending their time reprocessing information they already have. However, as a result of their lack of prejudice, less time overall will be wasted in endless debate among stubborn and potentially biased bees. Among the ants, the opinions of nest-mates are also pooled effectively when scouts use a threshold population of their nest-mates present in a new nest-site as a cue to switch to more rapid recruitment. Furthermore, the ants'' reluctance to begin recruiting to poor nest-sites means that more time is available for the discovery and direct comparison of alternatives. Likewise, the retirement of honeybee scouts from dancing for a given site allows more time for other scouts to find potentially better sites. Thus, both the ants and the bees have time-lags built into their decision-making systems that should facilitate a compromise between thorough surveys for good nest-sites and relatively rapid decisions. We have also been able to show that classical mathematical models can illuminate the processes by which colonies are able to achieve decisions that are relatively swift and very well informed.     

Ants move to improve: colonies of Leptothorax albipennis emigrate whenever they find a superior nest site

A high-quality home can be a major factor determining fitness. However, when house hunting becomes necessary, animals might often face a speed-versus-accuracy trade-off and therefore be unable to survey their environment extensively for the optimum site. We found that the ant Leptothorax albipennis was able to correct errors made in such a hurried decision by continuing to survey even after a colony had settled in a nest site. Colonies moved from intact undisturbed nests to another nest site whenever the new nest site presented a sufficient improvement in nest quality. Thus, scout ants must be able to judge and compare the quality of the new, empty nest site with the one currently inhabited by the colony. Emigrations from intact nests were initiated by high numbers of ants recruited by tandem runs. This evidence may explain how a small number of scouts can motivate an entire colony to move when there is no immediate need to do so. Compared with their behaviour in emigrations from destroyed nests, the ants favoured even more strongly accuracy over speed, because they waited for a larger number of scouts to agree on one site before starting the emigration. They could do this without increased risk because the rest of the colony remained safely in the old nest.     

Age and Behavior of Honey Bee Workers,Apis mellifera,that Interact with Drones

Colony reproduction in honey bees involves complex interactions between sterile workers and reproductive castes. Although worker–queen interactions have been studied in detail, worker–drone interactions are less well understood. We investigated caste interactions in honey bees by determining the age and behavior of workers that perform vibration signals, trophallaxis, and grooming with drones. Workers of all ages could engage in the different interactions monitored, although workers that performed vibration signals on drones were significantly older than those engaging in trophallaxis and grooming. Only 3–8% of workers engaged in the different behaviors were monitored. Compared with workers that performed vibration signals only on workers (‘worker vibrators’), those that performed signals on both workers and drones (‘drone vibrators’) had greater movement rates inside the nest, higher vibration signaling rates, and were more likely to have an immediate association with foraging. Both worker vibrators and drone vibrators contacted drones of all ages as they moved through the nest. However, drone vibrators contacted drones at higher rates, contacted slightly, but significantly younger drones, and were more likely to engage in trophallaxis and grooming with drones, in addition to vibrating them. Taken together, our results suggest that tiny proportions of workers belonging to separate, but overlapping age groups provide most of the care received by adult drones, and that drone vibrators comprise a subset of signalers within a colony that have an increased tendency to contact and interact with drones. Vibratory, tactile signals are involved in colony reproductive and movement decisions in a number of species of bees, wasps and ants, and may provide valuable tools for investigating caste interactions in many insect societies.     

Deciding on the wing: in-flight decision making and search space sampling in the red dwarf honeybee Apis florea

During reproductive swarming and seasonal migration, a honeybee swarm needs to locate and move to a new, suitable nest site. While the nest-site selection process in cavity-nesting species such as the European honeybee Apis mellifera is very precise with the swarm carefully selecting a single site, open-nesting species, such as Apis florea, lack such precision. These differences in precision in the nest-site selection process are thought to arise from the differing nest-site requirements of open- and cavity-nesting species. While A. florea can nest on almost any tree, A. mellifera is constrained by the scarcity of suitable nest sites. Here we show that imprecision in the nest-site selection process allows swarms to quickly reach a decision when many nest sites are available. In contrast, a very precise nest-site selection process slows down the decision-making process when nest sites are abundant.     

Waggle dances in absconding colonies of the red dwarf honeybee, Apis florea

The directional information encoded in the waggle dances of absconding colonies of Apis florea shows how different sites are advertised during decision-making. Colonies of A. florea were observed from the inception of absconding until the swarm settled at a new nest site. The number of waggle dancers at the beginning of the absconding sequence was low, gradually increased and then declined shortly before liftoff. During the last 2 to 0.5?h before liftoff, the dances still indicated different directions. This significantly decreased in the last 0.5?h until only one or two dance directions were being advertised. All colonies reached a near consensus in the last 20 dances before liftoff. The swarm flight path is meandering so the actual distance flown is about twice that indicated by the dances. During the last 3?min the waggle dance in most colonies showed nest target angles that were closely clustered indicating that the final directions advertised were close to the chosen target site. In all absconding/migratory species of honeybees thus far studied, there is a special dance associated with absconding that appears not to select specific destinations but rather a particular direction in search of a new nesting area.     

How does food distance influence foraging in the ant Lasius niger: the importance of home-range marking

We study the influence of food distance on the individual foraging behaviour of Lasius niger scouts and we investigate which cue they use to assess their distance from the nest and accordingly tune their recruiting behaviour. Globally, the number of U-turns made by scouts increases with distance resulting in longer travel times and duration of the foraging cycle. However, over familiar areas, home-range marking reduces the frequency and thereby the impact of U-turns on foraging times leading to a quicker exploitation of food sources than over unmarked set-ups. Regarding information transfer, the intensity of the recruitment trail reaching the nest decreases with increasing food distance for all set-ups and is even more reduced in the absence of home-range marking. Hence, the probability of a scout continuing to lay a trail changes along the homeward journey but in a different way according to home-range marking. Over unexplored setups, at a given distance from the food source, the percentage of returning trail-laying ants remains unchanged for all tested nest-feeder distances. Hence, the tuning of the trail recruiting signal by scouts was not influenced by an odometric estimate of the distance already travelled by the ants during their outward journey to the food. By contrast, over previously explored set-ups, a distance-related factor – that is the intensity of home-range marking – strongly influences their recruiting behaviour. In fact, over a home-range marked bridge, the probability of returning ants maintaining their trail-laying behaviour increases with decreasing food distance while the gradient of home-range marks even induces ants which have stopped laying a trail to resume this behaviour in the nest vicinity. We suggest that home-range marking laid passively by walking ants is a relevant cue for scouts to indirectly assess distance from the nest but also local activity level or foraging risks in order to adaptively tune trail recruitment and colony foraging dynamics. Received 13 July 2004; revised 26 January and 20 May 2005; accepted 2 July 2005.     

Stop-Signaling Reduces Split Decisions without Impairing Accuracy in the Honeybee Nest-Site Selection Process

In the honeybee swarm nest-site selection process, individual bees gather information about available candidate sites and communicate the information to other bees. The swarm makes an agreement for a candidate site when the number of bees that supports the site reaches a threshold. This threshold is usually referred to as the quorum threshold and it is shown by many studies as a key parameter that is a compromise between the accuracy and speed of decisions. In the present work, we use a model of the honeybee Apis mellifera nest-site selection process to study how the quorum threshold and discovery time of candidate sites have major impact on two unfavorable situations in selecting a nest site: decision deadlock and decision split. We show that cross-inhibitory stop-signaling, delivered among bees supporting different sites, enables swarms to avoid the decision split problem in addition to avoiding the decision deadlock problem that has been previously proposed. We also show that stop-signaling improves decision speed, but compromises decision accuracy in swarms using high quorum thresholds by causing the swarms to be trapped in local optima (e.g., choosing a sub-optimal option that is encountered first). On the other hand, we demonstrate that stop-signaling can reduce split decisions without compromising decision accuracy in swarms using low quorum thresholds when it is compared to the accuracy of swarms using the same threshold values but not exhibiting stop-signaling. Based on our simulations, we suggest that swarms using low quorum thresholds (as well as swarms with large population sizes) would benefit more from exhibiting the stop-signaling activity than not exhibiting it.     

Provisioning habitat with custom‐designed nest‐boxes increases reproductive success in an endangered finch

Manipulating resource availability to assess the strength and effects of resource limitation on an animal population is relatively straightforward, and thus, common in the scientific literature. Resource quality, however, is rarely manipulated, as this requires a priori knowledge of a relationship between some measurable variation in the resource and individual preference and/or fitness. Recent research on nest‐site selection was used to inform the design of custom‐built nest‐boxes for an endangered hollow‐nester, the Gouldian finch (Erythrura gouldiae). By provisioning breeding populations with these ‘high quality’ artificial nest sites over 3 years, we experimentally investigated the strength and effects of nest‐site limitation in this species. Breeding pairs using nest‐boxes initiated nesting earlier, produced larger clutches and fledged more offspring per season than those in natural hollows. Total and mean reproductive output also increased in nest‐box provisioned sites over the duration of the study. All of these effects were predominantly driven by pairs initiating clutches earlier, potentially because of the reduced intra‐ and interspecific competition for nest sites at optimal breeding times. Our findings suggest that reproduction in wild Gouldian finch populations may be limited by the availability of high quality nest sites in the landscape, and that nest‐boxes could be used as a tool for enhancing reproduction in recovering populations. Furthermore, we conclude that resource quality is equally, if not more important than quantity when supplementing resource‐limited habitats.     

Comparative brain transcriptomic analyses of scouting across distinct behavioural and ecological contexts in honeybees

Individual differences in behaviour are often consistent across time and contexts, but it is not clear whether such consistency is reflected at the molecular level. We explored this issue by studying scouting in honeybees in two different behavioural and ecological contexts: finding new sources of floral food resources and finding a new nest site. Brain gene expression profiles in food-source and nest-site scouts showed a significant overlap, despite large expression differences associated with the two different contexts. Class prediction and ‘leave-one-out’ cross-validation analyses revealed that a bee''s role as a scout in either context could be predicted with 92.5% success using 89 genes at minimum. We also found that genes related to four neurotransmitter systems were part of a shared brain molecular signature in both types of scouts, and the two types of scouts were more similar for genes related to glutamate and GABA than catecholamine or acetylcholine signalling. These results indicate that consistent behavioural tendencies across different ecological contexts involve a mixture of similarities and differences in brain gene expression.     

The significance of visual landmarks for navigation of the giant tropical ant,Paraponera clavata (Formicidae,Ponerinae)

Summary Workers of the giant tropical ant,Paraponera clavata, use trail pheromones for orientation and recruitment of nestmates. However, chemical markings may not always be sufficient for successful navigation in complex three-dimensional terrain, and additional orientation cues may be required. Behavioral field experiments were performed to investigate the significance of visual landmarks for homing foragers. Animals which were prevented from seeing the canopy were unable to navigate back to the nest, even though trail pheromones were still present. In contrast, foragers found their way back to the nest after their trail pheromones had been abolished but their visual scenes remained unchanged. This emphasizes the important role of visual landmarks during spatial orientation in homingP. clavata foragers. Individually foraging scouts were discovered in the understory of the forest floor up to 30 m away from their nest. They were rewarded, and displaced between 0.8 m and 13.6 m. Fifteen out of 16 animals had no difficulties in finding the nest entrance despite the altered appearance of local and distant landmarks at the release site. Apparently the scouts were able to recognize the visual scenes at the release site, and used them for reference to locate the nest entrance. In contrast, ants displaced from their nest to sites around 4 m away had more difficulties to re-find the nest.     

A Mathematical Model for Flight Guidance in Honeybee Swarms

When a colony of honeybees relocates to a new nest site, less than 5?% of the bees (the scout bees) know the location of the new nest. Nevertheless, the small minority of informed bees manages to provide guidance to the rest and the entire swarm is able to fly to the new nest intact. The streaker bee hypothesis, one of the several theories proposed to explain the guidance mechanism in bee swarms, seems to be supported by recent experimental observations. The theory suggests that the informed bees make high-speed flights through the swarm in the direction of the new nest, hence conspicuously pointing to the desired direction of travel. This work presents a mathematical model of flight guidance in bee swarms based on the streaker bee hypothesis. Numerical experiments, parameter studies, and comparison with experimental data are presented.     

Behavior during artifically induced swarm emigration in an old world polistine wasp,Ropalidia romandi (Hymenoptera: Vespidae)

Absconding swarms of the Australian swarm-founding wasp,Ropalidia romandi, were artificially induced. Workers may initially search for new nesting sites and once a new nest site is decided, they recruit their nest mates including multiple queens there. During the swarm emigration, workers often land on prominent objects, such as tree leaves, and drag the metasoma; those that do not drag usually antennate the object surfaces. These findings suggest thatR. romandi workers use a scent trail during swarm emigration. Artificial transfer of colonies resulted in clustering of wasps from different colonies, indicating thatR. romandi may not act exclusively against non-nestmates. In the formation of tentative aggregation of wasps prior to commencing emigration, and also in recognizing a new nesting site by following swarm members that have been guided by a scent trail, a visual cue (aerial swarm formed around an aggregation of wasps) seems to play an important role.     

Ants estimate area using Buffon's needle

We show for the first time, to our knowledge, that ants can measure the size of potential nest sites. Nest size assessment is by individual scouts. Such scouts always make more than one visit to a potential nest before initiating an emigration of their nest mates and they deploy individual-specific trails within the potential new nest on their first visit. We test three alternative hypotheses for the way in which scouts might measure nests. Experiments indicated that individual scouts use the intersection frequency between their own paths to assess nest areas. These results are consistent with ants using a 'Buffon's needle algorithm' to assess nest areas.