Experience,but not distance,influences the recruitment precision in the stingless bee <Emphasis Type="Italic">Scaptotrigona mexicana</Emphasis>

Recruitment precision, i.e. the proportion of recruits that reach an advertised food source, is a crucial adaptation of social bees to their environment. Studies with honeybees showed that recruitment precision is not a fixed feature, but it may be enhanced by factors like experience and distance. However, little is known regarding the recruitment precision of stingless bees. Hence, in this study, we examined the effects of experience and spatial distance on the precision of the food communication system of the stingless bee Scaptotrigona mexicana. We conducted the experiments by training bees to a three-dimensional artificial patch at several distances from the colony. We recorded the choices of individual recruited foragers, either being newcomers (foragers without experience with the advertised food source) or experienced (foragers that had previously visited the feeder). We found that the average precision of newcomers (95.6 ± 2.61%) was significantly higher than that of experienced bees (80.2 ± 1.12%). While this might seem counter-intuitive on first sight, this “loss” of precision can be explained by the tendency of experienced recruits to explore nearby areas to find new rewarding food sources after they had initially learned the exact location of the food source. Increasing the distance from the colony had no significant effect on the precision of the foraging bees. Thus, our data show that experience, but not the distance of the food source, affected the patch precision of S. mexicana foragers.     

Yellowjackets use nest-based cues to differentially exploit higher-quality resources

While foraging, social insects encounter a dynamic array of food resources of varying quality and profitability. Because food acquisition influences colony growth and fitness, natural selection can be expected to favor colonies that allocate their overall foraging effort so as to maximize their intake of high-quality nutrients. Social wasps lack recruitment communication, but previous studies of vespine wasps have shown that olfactory cues influence foraging decisions. Odors associated with food brought into the nest by successful foragers prompt naive foragers to leave the nest and search for the source of those odors. Left unanswered, however, is the question of whether naive foragers take food quality into account in making their decisions about whether or not to search. In this study, two different concentrations of sucrose solutions, scented differently, were inserted directly into each of three Vespula germanica nests. At a feeder away from the nest, arriving foragers were given a choice between two 1.5 M sucrose solutions with the same scents as those in the nest. We show that wasps chose higher-quality resources in the field using information in the form of intranidal food-associated odor cues. By this simple mechanism, the colony can bias the allocation of its foraging effort toward higher-quality resources in the environment.     

Foraging reactivation in the honeybee Apis mellifera L.: factors affecting the return to known nectar sources

This paper addresses, what determines that experienced forager honeybees return to places where they have previously exploited nectar. Although there was already some evidence that dance and trophallaxis can cause bees to return to feed, the fraction of unemployed foragers that follow dance or receive food from employed foragers before revisiting the feeder was unknown. We found that 27% of the experienced foragers had no contact with the returning foragers inside the hive. The most common interactions were dance following (64%) and trophallaxis (21%). The great variability found in the amount of interactions suggests that individual bees require different stimulation before changing to the foraging mode. This broad disparity negatively correlated with the number of days after marking at the feeder, a variable that is closely related to the foraging experience, suggesting that a temporal variable might affect the decision-making in reactivated foragers.     

The cues have it; nest-based, cue-mediated recruitment to carbohydrate resources in a swarm-founding social wasp

This study explores whether or not foragers of the Neotropical swarm-founding wasp Polybia occidentalis use nest-based recruitment to direct colony mates to carbohydrate resources. Recruitment allows social insect colonies to rapidly exploit ephemeral resources, an ability especially advantageous to species such as P. occidentalis, which store nectar and prey in their nests. Although recruitment is often defined as being strictly signal mediated, it can also occur via cue-mediated information transfer. Previous studies indicated that P. occidentalis employs local enhancement, a type of cue-mediated recruitment in which the presence of conspecifics at a site attracts foragers. This recruitment is resource-based, and as such, is a blunt recruitment tool, which does not exclude non-colony mates. We therefore investigated whether P. occidentalis also employs a form of nest-based recruitment. A scented sucrose solution was applied directly to the nest. This mimicked a scented carbohydrate resource brought back by employed foragers, but, as foragers were not allowed to return to the nest with the resource, there was no possibility for on-nest recruitment behavior. Foragers were offered two dishes—one containing the test scent and the other an alternate scent. Foragers chose the test scent more often, signifying that its presence in the nest induces naïve foragers to search for it off-nest. P. occidentalis, therefore, employs a form of nest-based recruitment to carbohydrate resources that is mediated by a cue, the presence of a scented resource in the nest.     

How floral odours are learned inside the bumblebee (Bombus terrestris) nest

Recruitment in social insects often involves not only inducing nestmates to leave the nest, but also communicating crucial information about finding profitable food sources. Although bumblebees transmit chemosensory information (floral scent), the transmission mechanism is unknown as mouth-to-mouth fluid transfer (as in honeybees) does not occur. Because recruiting bumblebees release a pheromone in the nest that triggers foraging in previously inactive workers, we tested whether this pheromone helps workers learn currently rewarding floral odours, as found in food social learning in rats. We exposed colonies to artificial recruitment pheromone, paired with anise scent. The pheromone did not facilitate learning of floral scent. However, we found that releasing floral scent in the air of the colony was sufficient to trigger learning and that learning performance was improved when the chemosensory cue was provided in the nectar in honeypots; probably because it guarantees a tighter link between scent and reward, and possibly because gustatory cues are involved in addition to olfaction. Scent learning was maximal when anise-scented nectar was brought into the nest by demonstrator foragers, suggesting that previously unidentified cues provided by successful foragers play an important role in nestmates learning new floral odours.     

Floral odor learning within the hive affects honeybees’ foraging decisions

Honeybees learn odor cues quickly and efficiently when visiting rewarding flowers. Memorization of these cues facilitates the localization and recognition of food sources during foraging flights. Bees can also use information gained inside the hive during social interactions with successful foragers. An important information cue that can be learned during these interactions is food odor. However, little is known about how floral odors learned in the hive affect later decisions of foragers in the field. We studied the effect of food scent on foraging preferences when this learning is acquired directly inside the hive. By using in-hive feeders that were removed 24 h before the test, we showed that foragers use the odor information acquired during a 3-day stimulation period with a scented solution during a food-choice situation outside the nest. This bias in food preference is maintained even 24 h after the replacement of all the hive combs. Thus, without being previously collected outside by foragers, food odors learned within the hive can be used during short-range foraging flights. Moreover, correct landings at a dual-choice device after replacing the storing combs suggests that long-term memories formed within the colony can be retrieved while bees search for food in the field.     

Trophallaxis in filled-crop honeybees (Apis mellifera L.): food-loading time affects unloading behaviour

 Honeybees ingested 50% w/w (1.8 M) sucrose solution at a rate feeder offering either 16.5, 32.5 or 65 μl/min. While the time spent ingesting solution at the feeder decreased significantly with increasing flow of solution, bees attained maximum crop loads with this range of flows. Different parameters related to mouth-to-mouth food exchange (trophallaxis) showed important modulations as the offered flow of solution was incremented. Trophallactic transfer rate, i.e. the speed at which liquid food is transferred from donor to recipient bee, was found to increase along with increasing profitability at the rate feeder. In the present case, food source profitability could have been evaluated by foragers either by measuring the time invested in ingesting the solution, or by direct assessment of the flow rate of the feeder. Thus it seems that perception of profitability conditions at the food sourcesuffices for later representation in the hive through trophallactic contacts, independently of crop-filling state. Received: 10 March 2000 / Accepted in revised form: 19 April 2000     

Recruits of the stingless bee Scaptotrigona pectoralis learn food odors from the nest atmosphere

The ability to learn food odors inside the nest and to associate them with food sources in the field is of essential importance for the recruitment of nestmates in social bees. We investigated odor learning by workers within the hive and the influence of these odors on their food choice in the field in the stingless bee Scaptotrigona pectoralis. During the experiments, recruited bees had to choose between two feeders, one with an odor that was present inside the nest during the recruitment process, and one with an unknown odor. In all experiments with different odor combinations (linalool/phenylacetaldehyde, geraniol/eugenol) a significant majority of bees visited the feeder with the odor they had experienced in their nest (χ ²-tests; p?<?0.05). By contrast, the bees showed no preference for one of two feeders when they were either baited with the same odor (linalool) or contained no odor. Our results clearly show that naïve workers of S. pectoralis can learn the odor of a food source during the recruitment process from the nest atmosphere and that their subsequent food search in the field is influenced by the learned odor.     

Chemical compounds of the foraging recruitment pheromone in bumblebees

When the frenzied and irregular food-recruitment dances of bumblebees were first discovered, it was thought that they might represent an evolutionary prototype to the honeybee waggle dance. It later emerged that the primary function of the bumblebee dance was the distribution of an alerting pheromone. Here, we identify the chemical compounds of the bumblebee recruitment pheromone and their behaviour effects. The presence of two monoterpenes and one sesquiterpene (eucalyptol, ocimene and farnesol) in the nest airspace and in the tergal glands increases strongly during foraging. Of these, eucalyptol has the strongest recruitment effect when a bee nest is experimentally exposed to it. Since honeybees use terpenes for marking food sources rather than recruiting foragers inside the nest, this suggests independent evolutionary roots of food recruitment in these two groups of bees.     

Communal nesting and kinship in degus (<Emphasis Type="Italic">Octodon degus</Emphasis>)

Communal nesting is a fundamental component of many animal societies. Because the fitness consequences of this behavior vary with the relatedness among nest mates, understanding the kin structure of communally nesting groups is critical to understanding why such groups form. Observations of captive degus (Octodon degus) indicate that multiple females nest together, even when supplied with several nest boxes. To determine whether free-living degus also engage in communal nesting, we used radiotelemetry to monitor spatial relationships among adult females in a population of O. degus in central Chile. These analyses revealed that females formed stable associations of > 2–4 individuals, all of whom shared the same nest site at night. During the daytime, spatial overlap and frequency of social interactions were greatest among co-nesting females, suggesting that nesting associations represent distinct social units. To assess kinship among co-nesting females, we examined genotypic variation in our study animals at six microsatellite loci. These analyses indicated that mean pairwise relatedness among members of a nesting association (r=0.25) was significantly greater than that among randomly selected females (r=–0.03). Thus, communally nesting groups of degus are composed of female kin, making it possible for indirect as well as direct fitness benefits to contribute to sociality in this species.     

Nest odor dynamics in the social wasp Vespula vulgaris

We investigated nest odor dynamics in the common yellow jacket, Vespula vulgaris. In six isolated colonies, we tested the aggression rates toward dead nestmates that had been stored for 10 min, 10 and 19 days outside their colonies at –76 °C. The aggression rate increased from about 12% toward recently killed nestmates up to 30% toward nestmates killed 19 days before the experiment. Obviously, the conserved nest odor profile of the nestmates frozen for several days did not match with that of their colony anymore. This indicates a change of the nest odor within the colony. In a second experiment, we kept two colonies each in one nest box with a complete separation of both neighbor nests by a solid wall inside the box for 28 days. In confrontation experiments, the colony members treated dead foragers from the neighbor nest as aggressively as dead foreign, non-neighbor workers (about 39% each) whereas only about 14% reacted aggressively toward dead nestmates. Seventeen days after the replacement of the solid wall by a metallic grid, which allowed no physical contact but air exchange between the two neighbor colonies, the aggression rates toward foreign workers and nestmates remained relatively unaffected whereas it decreased significantly toward dead neighbors to about 11%. These results suggest a nest odor dynamic caused by volatiles transferred between two adjacent colonies, resulting in an equalization of the former colony specific nest odors. A change of nest odor dynamics influenced by volatiles was so far described only for one ant species at all.     

The emergence of collective foraging in the arboreal<Emphasis Type="Italic"> Gnamptogenys menadensis</Emphasis> (Hymenoptera: Formicidae)

Gnamptogenys menadensis is an arboreal nester that forages opportunistically almost exclusively on vegetation, sometimes recruiting others to participate in prey retrieval. The three-dimensional characteristics of vegetation suggest that functions describing recruitment decision thresholds or the pattern of recruitment in arboreal species may differ from those predicted by optimal foraging theory. To examine the effects of prey abundance and distance on the recruitment dynamics of G. menadensis, we baited nests with one termite, five termites or a number of termites between 20 and 40 either near to or far from the entrance and observed the ensuing behaviors. G. menadensis recruited others when encountering multiple termites regardless of the termite pile's distance from the nest, although a few individuals remained at the site and defended the resource. The pattern of arrivals at the site indicates that the majority and sometimes all arrivals were recruited from the branch trails. In combination, these results suggest that the architecture of the foraging habitat, which limits available return routes to the nest and thus increases encounter probabilities with potential recruits, shaped the process of information transfer and generated a collective pattern of foraging and prey retrieval.     

Non-random nectar unloading interactions between foragers and their receivers in the honeybee hive

Nectar acquisition in the honeybee Apis mellifera is a partitioned task in which foragers gather nectar and bring it to the hive, where nest mates unload via trophallaxis (i.e. mouth-to-mouth transfer) the collected food for further storage. Because forager mates exploit different feeding places simultaneously, this study addresses the question of whether nectar unloading interactions between foragers and hive-bees are established randomly, as it is commonly assumed. Two groups of foragers were trained to exploit a different scented food source for 5 days. We recorded their trophallaxes with hive-mates, marking the latter ones according to the forager group they were unloading. We found non-random probabilities for the occurrence of trophallaxes between experimental foragers and hive-bees, instead, we found that trophallactic interactions were more likely to involve groups of individuals which had formerly interacted orally. We propose that olfactory cues present in the transferred nectar promoted the observed bias, and we discuss this bias in the context of the organization of nectar acquisition: a partitioned task carried out in a decentralized insect society.     

An absence of aggression between non-nestmates in the bull ant <Emphasis Type="Italic">Myrmecia nigriceps</Emphasis>

The ability of social insects to discriminate against non-nestmates is vital for maintaining colony integrity, and in most social insect species, individuals act aggressively towards non-nestmates that intrude into their nest. Our experimental field data revealed that intra-colony aggression in the primitive bulldog ant Myrmecia nigriceps is negligible; our series of bioassays revealed no significant difference in the occurrence of aggression in trials involving workers from the same, a close (less than 300 m) or a far (more than 1.5 km) nest. Further, non-nestmate intruders were able to enter the nest in 60% of our trials; a similar level was observed in trials involving nestmates. These results suggest that workers of M. nigriceps are either unable to recognize alien conspecifics or that the costs of ignoring workers from foreign colonies are sufficiently low to favor low levels of inter-colony aggression in this species.     

Bee-hawking by the wasp, <Emphasis Type="BoldItalic">Vespa velutina</Emphasis>, on the honeybees <Emphasis Type="BoldItalic">Apis cerana</Emphasis> and <Emphasis Type="BoldItalic">A</Emphasis>. <Emphasis Type="BoldItalic">mellifera</Emphasis>

The vespine wasps, Vespa velutina, specialise in hawking honeybee foragers returning to their nests. We studied their behaviour in China using native Apis cerana and introduced A. mellifera colonies. When the wasps are hawking, A. cerana recruits threefold more guard bees to stave off predation than A. mellifera. The former also utilises wing shimmering as a visual pattern disruption mechanism, which is not shown by A. mellifera. A. cerana foragers halve the time of normal flight needed to dart into the nest entrance, while A. mellifera actually slows down in sashaying flight manoeuvres. V. velutina preferentially hawks A. mellifera foragers when both A. mellifera and A. cerana occur in the same apiary. The pace of wasp-hawking was highest in mid-summer but the frequency of hawking wasps was three times higher at A. mellifera colonies than at the A. cerana colonies. The wasps were taking A. mellifera foragers at a frequency eightfold greater than A. cerana foragers. The final hawking success rates of the wasps were about three times higher for A. mellifera foragers than for A. cerana. The relative success of native A. cerana over European A. mellifera in thwarting predation by the wasp V. velutina is interpreted as the result of co-evolution between the Asian wasp and honeybee, respectively.     

The eyes of oilbirds (<Emphasis Type="Italic">Steatornis caripensis</Emphasis>): pushing at the limits of sensitivity

An extreme example of a low light-level lifestyle among flying birds is provided by the oilbird, Steatornis caripensis (Steatornithidae, Caprimulgiformes). Oilbirds breed and roost in caves, often at sufficient depth that no daylight can penetrate, and forage for fruits at night. Using standard microscopy techniques we investigated the retinal structure of oilbird eyes and used an ophthalmoscopic reflex technique to determine the parameters of these birds visual fields. The retina is dominated by small rod receptors (diameter 1.3±0.2 m; length 18.6±0.6 m) arranged in a banked structure that is unique among terrestrial vertebrates. This arrangement achieves a photoreceptor density that is the highest so far recorded (1,000,000 rods mm^–2) in any vertebrate eye. Cone photoreceptors are, however, present in low numbers. The eye is relatively small (axial length 16.1±0.2 mm) with a maximum pupil diameter of 9.0±0.0 mm, achieving a light-gathering capacity that is the highest recorded in a bird (f-number 1.07). The binocular field has a maximum width of 38° and extends vertically through 100° with the bill projecting towards the lower periphery; a topography that suggests that vision is not used to control bill position. We propose that oilbird eyes are at one end of the continuum that juxtaposes the conflicting fundamental visual capacities of sensitivity and resolution. Thus, while oilbird visual sensitivity may be close to a maximum, visual resolution must be low. This explains why these birds employ other sensory cues, including olfaction and echolocation, in the control of their behaviour in low-light-level environments.     

Tandem carrying,a new foraging strategy in ants: description,function, and adaptive significance relative to other described foraging strategies

An important aspect of social insect biology lies in the expression of collective foraging strategies developed to exploit food. In ants, four main types of foraging strategies are typically recognized based on the intensity of recruitment and the importance of chemical communication. Here, we describe a new type of foraging strategy, “tandem carrying”, which is also one of the most simple recruitment strategies, observed in the Ponerinae species Pachycondyla chinensis. Within this strategy, workers are directly carried individually and then released on the food resource by a successful scout. We demonstrate that this recruitment is context dependent and based on the type of food discovered and can be quickly adjusted as food quality changes. We did not detect trail marking by tandem-carrying workers. We conclude by discussing the importance of tandem carrying in an evolutionary context relative to other modes of recruitment in foraging and nest emigration.     

RNAi-mediated silencing of vitellogenin gene function turns honeybee (Apis mellifera) workers into extremely precocious foragers

The switch from within-hive activities to foraging behavior is a major transition in the life cycle of a honeybee (Apis mellifera) worker. A prominent regulatory role in this switch has long been attributed to juvenile hormone (JH), but recent evidence also points to the yolk precursor protein vitellogenin as a major player in behavioral development. In the present study, we injected vitellogenin double-stranded RNA (dsVg) into newly emerged worker bees of Africanized genetic origin and introduced them together with controls into observation hives to record flight behavior. RNA interference-mediated silencing of vitellogenin gene function shifted the onset of long-duration flights (>10 min) to earlier in life (by 3–4 days) when compared with sham and untreated control bees. In fact, dsVg bees were observed conducting such flights extremely precociously, when only 3 days old. Short-duration flights (<10 min), which bees usually perform for orientation and cleaning, were not affected. Additionally, we found that the JH titer in dsVg bees collected after 7 days was not significantly different from the controls. The finding that depletion of the vitellogenin titer can drive young bees to become extremely precocious foragers could imply that vitellogenin is the primary switch signal. At this young age, downregulation of vitellogenin gene activity apparently had little effect on the JH titer. As this unexpected finding stands in contrast with previous results on the vitellogenin/JH interaction at a later age, when bees normally become foragers, we propose a three-step sequence in the constellation of physiological parameters underlying behavioral development. David Santos Marco Antonio and Karina Rosa Guidugli-Lazzarini contributed equally to the present study.     

A trail pheromone component of the ant Mayriella overbecki Viehmeyer (Formicidae: Myrmicinae)

 The myrmicine ant Mayriella overbecki lays recruitment trails during foraging and nest emigrations. The trail pheromone originates from the poison gland. From ten identified components of the poison gland secretions only methyl 6-methylsalicylate 1 elicited trail following behavior. Received: 6 April 2000 / Accepted in revised form: 6 June 2000     

In-nest environment modulates nestmate recognition in the ant<Emphasis Type="Italic"> Camponotus fellah</Emphasis>

Multiple behavioral and chemical studies indicate that ant nestmate recognition cues are low-volatile substances, in particular hydrocarbons (HCs) located on the cuticular surface. We tested the hypothesis that in the ant Camponotus fellah, nest environment, in particular nest volatile odors, can modulate nestmate-recognition-mediated aggression. Workers were individually confined within their own nest in small cages having either a single mesh (SM = limited physical contact permitted) or a double mesh (DM = exposed to nest volatiles only) screen. Individual workers completely isolated outside their nest (CI) served as control. When reintroduced into a group of 50 nestmates, the CI workers were attacked as alien ants after only 2 weeks of separation, whereas the SM workers were treated as nestmates even after 2 months of separation. Aggression towards DM ants depended on the period of isolation. Only DM workers isolated for over 2 months were aggressed by their nestmates, which did not significantly differ from the CI nestmates. Cuticular HC analyses revealed that the profile of the non-isolated ants (NI) was clearly distinct from that of CI, SM and DM ants. Profile differences matched the aggressive response in the case of CI ants but were uncorrelated in the case of SM or DM ants. This suggests that keeping the ants within the nest environment affected nestmate recognition in additional ways than merely altering their HC profile. Nest environment thus appears to affect label–template mismatch by modulating aggressive behavior, as well as the direction at which cuticular HCs diverged during the separation period.