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Bee-collected pollen and nectar contain multiple phytochemicals that can have anti-pathogenic effects when ingested. For example, the plant alkaloid, nicotine, can reduce infections by the trypanosome gut parasite (Crithidia bombi) in bumblebees. Parasitized bumblebees may be drawn to nicotine and thereby self-medicate their infection. We tested the hypothesis that nicotine can reduce infections of a common microsporidian pathogen, Nosema ceranae, in the honey bee gut. We found, however, that that a field realistic exposure dose of 1 ppm nicotine was not preferentially consumed by Apis mellifera foragers fed live Nosema spores (5 × 104 spores per bee; N = 160). One-day-old bees infected with Nosema (1 × 104 spores per bee; N = 160) showed no repression of nosemosis over a chronically applied exposure gradient of 0, 10−2, 10−1, 100, 101, 102, 103 or 104 ppm nicotine. Since imbibed nicotine may not effectively reach the spores in the bee gut, we conducted an in vitro experiment, in which Nosema spores were exposed up to 104 ppm nicotine in vials, rinsed of nicotine, and then fed to 1 day old bees (2 × 104 spores per bee; N = 216). However, the in vitro nicotine-treated spores remained infectious. Nicotine did impair bee mortality at high concentrations. Dietary nicotine is evidently not a treatment for nosemosis, but future studies should continue to examine the role of phytochemicals and bee health.

Recent declines in the abundance and diversity of wild bee species have made it important to understand how introduced species such as honey bees contribute to pollinating native plants. In this study, we decoded the waggle dances of Apis mellifera pollen foragers and used DNA barcoding of bee-collected pollen over 17 months to characterize spatio-temporal patterns in recruitment behavior and dietary breadth in a diverse yet fragmented Mediterranean scrub environment. Foragers danced for small, nearby patches of pollen resources during the cool dormant season but danced for 1.6–2.7-fold more distant and more widely dispersed resources during the hot dry season, a time of seasonal drought and floral dearth. Individual foragers collected pollen from a wide variety of species, but colonies focused recruitment on a small subset of common species in flower during each season: 2.7, 6.3, and 10% of all species in bloom during the dormant, growth, and dry seasons, respectively. Pollen foragers danced almost exclusively for cold-adapted native species during the dormant season, equally for native and non-native plants during the short growth season, and primarily for non-native ornamental species during the dry season. Our results suggest that honey bee recruitment behavior and dietary breadth may be influenced by seasonal changes in pollen resources. Furthermore, they indicate that honey bees may be useful in pollinating common native plants, and that non-native ornamental species can provide a major source of colony protein during a seasonal dearth of flowering native species.

While foraging, animals can form inter- and intraspecific social signalling networks to avoid similar predators. We report here that foragers of different native Asian honey bee species can detect and use a specialized alarm pheromone component, benzyl acetate (BA), to avoid danger. We analysed the volatile alarm pheromone produced by attacked workers of the most abundant native Asian honey bee, Apis cerana and tested the responses of other bee species to these alarm signals. As compared to nest guards, A. cerana foragers produced 3.38 fold higher levels of BA. In foragers, BA and (E)-dec-2-en-1-yl acetate (DA) generated the strongest antennal electrophysiological responses. BA was also the only compound that alerted flying foragers and inhibited A. cerana foraging. BA thereby decreased A. cerana foraging for risky sites. Interestingly, although BA occurs only in trace amounts and is nearly absent in sympatric honeybee species (respectively only 0.07% and 0.44% as much in A. dorsata and A. florea), these floral generalists detected and avoided BA as strongly as they did to their own alarm pheromone on natural inflorescences. These results demonstrate that competing pollinators can take advantage of alarm signal information provided by other species.

In highly social bees, queen mandibular pheromone (QMP) is vital for colony life. Both Apis cerana (Ac) and Apis mellifera (Am) share an evolutionarily conserved set of QMP compounds: (E)-9-oxodec-2-enoic acid (9-ODA), (E)-9-hydroxydec-2-enoic acid (9-HDA), (E)-10-hydroxy-dec-2-enoic acid (10-HDA), 10-hydroxy-decanoic acid (10-HDAA), and methyl p-hydroxybenzoate (HOB) found at similar levels. However, evidence suggests there may be species-specific sensitivity differences to QMP compounds because Ac workers have higher levels of ovarian activation than Am workers. Using electroantennograms, we found species-specific sensitivity differences for a blend of the major QMP compounds and three individual compounds (9-HDA, 10-HDAA, and 10-HDA). As predicted, Am was more sensitive than Ac in all cases (1.3- to 2.7- fold higher responses). There were also species differences in worker retinue attraction to three compounds (9-HDA, HOB, and 10-HDA). In all significantly different cases, Am workers were 4.5- to 6.2-fold more strongly attracted than Ac workers were. Thus, Ac workers responded less strongly to QMP than Am workers, and 9-HDA and 10-HDA consistently elicited stronger antennal and retinue formation responses [corrected].

Nectar guides can enhance pollinator efficiency and plant fitness by allowing pollinators to more rapidly find and remember the location of floral nectar. We tested if a radiating nectar guide around a nectary would enhance the ability of naïve bumble bee foragers to find nectar. Most experiments that test nectar guide efficacy, specifically radiating linear guides, have used guides positioned around the center of a radially symmetric flower, where nectaries are often found. However, the flower center may be intrinsically attractive. We therefore used an off-center guide and nectary and compared "conjunct" feeders with a nectar guide surrounding the nectary to "disjunct" feeders with a nectar guide separated from the nectary. We focused on the innate response of novice bee foragers that had never previously visited such feeders. We hypothesized that a disjunct nectar guide would conflict with the visual information provided by the nectary and negatively affect foraging. Approximately, equal numbers of bumble bees (Bombus impatiens) found nectar on both feeder types. On disjunct feeders, however, unsuccessful foragers spent significantly more time (on average 1.6-fold longer) searching for nectar than any other forager group. Successful foragers on disjunct feeders approached these feeders from random directions unlike successful foragers on conjunct feeders, which preferentially approached the combined nectary and nectar guide. Thus, the nectary and a surrounding nectar guide can be considered a combination of two signals that attract naïve foragers even when not in the floral center. © 2014 Springer-Verlag Berlin Heidelberg.

Foraging specialization plays an important role in the ability of social insects to efficiently allocate labor. However, relatively little is known about the degree to which individual bumble bees specialize on collecting nectar or pollen, when such preferences manifest, and if individuals can alter their foraging preferences in response to changes in the colony workforce. Using Bombus impatiens, we monitored all foraging visits made by every bee in multiple colonies and showed that individual foragers exhibit consistent lifetime foraging preferences. Based upon the distribution of foraging preferences, we defined three forager types (pollen specialists, nectar specialists, and generalists). In unmanipulated colonies, 16-36 % of individuals specialized (≥90 % of visits) on nectar or pollen only. On its first day of foraging, an individual's foraging choices (nectar only, pollen only, or nectar and pollen) significantly predicted its lifetime foraging preferences. Foragers that only collected pollen on their first day of foraging made 1.61- to 1.67-fold more lifetime pollen foraging visits (as a proportion of total trips) than foragers that only collected nectar on their first foraging day. Foragers were significantly larger than bees that stayed only in the nest. We also determined the effect of removing pollen specialists at early (brood present) or later (brood absent) stages in colony life. These results suggest that generalists can alter their foraging preferences in response to the loss of a small subset of foragers. Thus, bumble bees exhibit individual lifetime foraging preferences that are established early in life, but generalists may be able to adapt to colony needs.

Multimodal communication plays an important role in pollination biology. Bees have evolved multimodal communication to recruit nestmates to rewarding food sources. Highly social bees can use visual and chemical information to recruit nestmates to rich food sources. However, no studies have determined if this information is redundant or has an additive effect such that multimodal information is more attractive than either modality presented by itself to free-flying bees. We tested the effect of two modalities, forager-deposited odor marks and the visual presence of foragers, on the orientation of stingless bee (Scaptotrigona mexicana) recruits. Our results show that odor marks alone were significantly more attractive than multimodal information, and that multimodal information was significantly more attractive than visual forager presence alone. Given the high olfactory sensitivity and limited visual acuity of insects, odor marks likely attracted recruits over a greater distance than the visual presence of nestmates. Thus, multimodal information in S. mexicana is redundant, not additive, in terms of orientation to food sources.

The ability of a successful forager to activate colony foraging allows colonies to rapidly exploit ephemeral resources and is an important innovation in the evolution of sociality. We tested the ability of the species, Bombus occidentalis, to stimulate colony foraging for food varying in quality. We then analyzed the behavior of successful foragers inside the nest to learn more about potential foraging activation movements. The number of bees entering a foraging arena was positively correlated with food sucrose concentration (0.5, 1.0, and 2.5 M sucrose, equal to 16–65% w/w). Foragers spent significantly more time imbibing higher concentration solutions. Foragers then returned to the nest where they moved in elaborate paths at variable speeds. There was no significant effect of sucrose concentration on average forager velocity or time spent inside the nest. However, the length of a forager’s path inside the nest (total of all distances moved each 0.1 s) significantly increased with sucrose concentration. On average, individuals foraging on 2.5 M and 1.0 M solution walked paths respectively 1.6 fold and 1.4 longer than the paths of individuals foraging on 0.5 M solution. These longer paths could result in a greater number of nestmate contacts, a factor shown to be important in the activation of B. impatiens foragers and also reported in B. terrestris foragers.

Collective decision making in the social insects often proceeds via feedback cycles based on positive signaling. Negative signals have, however, been found in a few contexts in which costs exist for paying attention to no longer useful information. Here we incorporate new research on the specificity and context of the negative stop signal into an agent based model of honey bee foraging to explore the adaptive basis of negative signaling in the dance language. Our work suggests that the stop signal, by acting as a counterbalance to the waggle dance, allows colonies to rapidly shut down attacks on other colonies. This could be a key adaptation, as the costs of attacking a colony strong enough to defend itself are significant. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10905-010-9229-5) contains supplementary material, which is available to authorized users.

The regulation of protein collection through pollen foraging plays an important role in pollination and in the life of bee colonies that adjust their foraging to natural variation in pollen protein quality and temporal availability. Bumble bees occupy a wide range of habitats from the Nearctic to the Tropics in which they play an important role as pollinators. However, little is known about how a bumble bee colony regulates pollen collection. We manipulated protein quality and colony pollen stores in lab-reared colonies of the native North American bumble bee, Bombus impatiens. We debut evidence that bumble bee colony foraging levels and pollen storage behavior are tuned to the protein quality (range tested: 17–30% protein by dry mass) of pollen collected by foragers and to the amount of stored pollen inside the colony. Pollen foraging levels (number of bees exiting the nest) significantly increased by 55%, and the frequency with which foragers stored pollen in pots significantly increased by 233% for pollen with higher compared to lower protein quality. The number of foragers exiting the nest significantly decreased (by 28%) when we added one pollen load equivalent each 5 min to already high intranidal pollen stores. In addition, pollen odor pumped into the nest is sufficient to increase the number of exiting foragers by 27%. Foragers directly inspected pollen pots at a constant rate over 24 h, presumably to assess pollen levels. Thus, pollen stores can act as an information center regulating colony-level foraging according to pollen protein quality and colony need.

Nestmate foraging activation and interspecific variation in foraging activation is poorly understood in bumble bees, as compared to honey bees and stingless bees. We therefore investigated olfactory information flow and foraging activation in the New World bumble bee species, Bombus impatiens. We (1) tested the ability of foragers to associate forager-deposited odor marks with rewarding food, (2) determined whether potential foragers will seek out the food odor brought back by a successful forager, and (3) examined the role of intranidal tactile contacts in foraging activation. Bees learned to associate forager-deposited odor marks with rewarding food. They were significantly more attracted to an empty previously rewarding feeder presented at a random position within an array of eight previously non-rewarding feeders. However, foragers did not exhibit overall odor specificity for short-term, daily floral shifts. For two out of three tested scents, activated foragers did not significantly prefer the feeder providing the same scent as that brought back by a successful forager. Finally, bees contacted by the successful forager inside the nest were significantly more likely to leave the nest to forage (38.6% increase in attempts to feed from empty feeders) than were non-contacted bees. This is the first demonstration that tactile contact, a hypothesized evolutionary basal communication mechanism in the social corbiculate bees, is involved in bumble bee foraging activation.

Social insects can modulate body temperature to increase foraging efficiency; however, little is known about how the relative value of protein resources affects forager body temperature. Such regulation may be important given that colony growth is often limited by protein availability. In this paper, we present what are, to our knowledge, the first data for social insects showing that thoracic temperatures (T (th)) of foragers increase with the protein content of food resources. In an introduced population of western yellowjacket (Vespula pensylvanica), we measured T (th) of foragers collecting high-quality protein (100% canned chicken) and low-quality protein (50% canned chicken, 50% indigestible alpha-cellulose by volume) at different ambient air temperatures (T (a)). Wasps foraging on 100% chicken consistently exhibited higher T (th) compared to wasps foraging on 50% chicken. After correcting for T (a), the mean T (th) for wasps collecting 100% chicken were 1.98 degrees C higher than those of individuals collecting 50% chicken. We suggest that this mechanism may increase foraging efficiency in this and other social wasp species.

We show that the stingless bees Melipona panamica and Partamona peckolti have ah igh pre- cision of intra-patch recruitment that is influenced by forager-deposited odor marks in the field. We trained foragers to a 2.5 M sucrose feeder in the center of an array of five identical feeders (20 cm between feeders) at different distances and directions from the nest and measured the distribution of recruit visitations. In the free-foraging phase foragers could odor mark a filter paper around the experimental feeder, and in the odor-removal phase we substituted it each five minutes by a clean one. Significantly more recruits in both species chose the experimental feeder over the controls in the distance and directional arrays (P 0.034) and odor removal significantly decreased precision of recruitment in both species (P 0.034). Scent marks in both species thus play a significant role in orienting recruits to already known profitable food sources. odor marking / recruitment / stingless bees / intra-patch precision / Meliponini

Xenobiotics such as the neonicotinoid pesticide, imidacloprid, are used globally, but their effects on native bee species are poorly understood. We studied the effects of sublethal doses of imidacloprid on olfactory learning in the native honey bee species, Apis cerana, an important pollinator of agricultural and native plants throughout Asia. We provide the first evidence that imidacloprid can impair learning in A. cerana workers exposed as adults or as larvae. Adults that ingested a single imidacloprid dose as low as 0.1 ng/bee had significantly reduced olfactory learning acquisition, which was 1.6-fold higher in control bees. Longer-term learning (1-17 h after the last learning trial) was also impaired. Bees exposed as larvae to a total dose of 0.24 ng/bee did not have reduced survival to adulthood. However, these larval-treated bees had significantly impaired olfactory learning when tested as adults: control bees exhibited up to 4.8-fold better short-term learning acquisition, though longer-term learning was not affected. Thus, sublethal cognitive deficits elicited by neonicotinoids on a broad range of native bee species deserve further study.

Foragers of the stingless bees genus Melipona may produce intranidal sounds that are correlated with food location and quality. In this study, we provide the first detailed analysis of pulsed sounds produced by Melipona panamica foragers while feeding on a carbohydrate food source. We trained foragers to a 2.5-M sucrose feeder under normal, ambient temperature (23–33°C) and lower temperature (11–25°C) conditions. We recorded forager sounds under both conditions and tested the effect of temperature of the thorax, feeder plate, and air on sound temporal characteristics. Forager energetic expenditure and the number of pulses per visit were significantly higher in the cold condition than in the normal condition. Foragers spent a longer time at the feeder under the cold condition than during the normal condition. Interpulse durations were significantly shorter in the cold condition than in the normal condition and became progressively and significantly shorter at the end of each performance. Thus, pulse production increased before departure. Foragers increased their thoracic temperatures above ambient at all experimental air temperatures. Under chilled conditions, foragers had a significantly greater difference between thorax temperature and ambient air temperature than under normal conditions. Foragers must achieve a minimum flight muscle temperature before take-off, and thus forager sounds may be linked to muscle warm-up.

Group aggression influences communication and defense strategies in many social insect communities. Such aggression plays a particularly significant role in the lives of stingless bees, important native Neotropical pollinators, in which the battle for food resources can be deadly and critical to colony survival. However, the effects of group size on individual aggression levels and the spatio-temporal aggression strategy of communal aggressors have not been fully explored. We therefore investigated how group size affects the aggression levels and the spatio-temporal attack strategy (which body parts, and the amount of time spent in attacking each part) in close combats between Trigona spinipes foragers and a natural competitor, Melipona rufiventris. In all trials, T. spinipes foragers competitively excluded M. rufiventris foragers from nearby feeders, exhibiting four levels of aggressive behavior ranging from threat displays to prolonged grappling and decapitation. Surprisingly, aggression levels and spatial strategy corresponded to the size of group attacks. Larger groups of attackers used individually lower aggression levels than small groups of attackers. Smaller groups also attacked appendages linked to escape (legs and wings) with greater frequency than larger groups, which focused on vital central body areas (abdomen, thorax, and head). Increased aggression corresponded to increased risks for attackers and the attacked. All combatants engaging at the highest level of aggression died (100% mortality). Thus the dominance style of T. spinipes may minimize attack risk and maximize victim harm with finely tuned hostility.

It is unclear whether stingless bees in the genus Melipona (Hymenoptera, Apidae, Meliponini) can reli- ably encode the distance to a food source through recruitment sounds produced inside the nest, in part because the sound features correlated with distance also vary with food quality. We therefore trained marked foragers of two species, Melipona mandacaia and M. bicolor, to feeders at different distances and to different sucrose concentrations at the same distance. In both species, foragers successfully recruited to a rich 2.5-m food source and produced pulsed recruitment sounds in which pulse duration was significantly and positively correlated with distance to the rich food source. When returning from poorer food sources (0.6-1.5 m), foragers of both species decreased sound production, producing shorter sound pulses and longer sound interpulses than they did for 2.5 m food located at the same distance. Thus the temporal structure of M. mandacaia and M. bicolor recruitment sounds varies with distance and food quality. However, nestmates were not recruited by performances for poorer food sources (0.6-1.5 m), whose sucrose concentration was sufficiently low to affect recruitment sounds. Surprisingly, the interphase (the time between behavioral phases that communicate location) also in- creases with decreasing food quality in the closely related honeybees (Apis), suggesting a potential homology in the effect of food quality on the recruitment systems of Apis and Melipona. We explore the evolutionary implications of these similarities.

Social bees can deposit specialized glandular secretions, or signals, that allow foragers to revisit rewarding and to avoid unrewarding food sources. However, it is not known if bees can orient towards olfactory cues such as excreta deposited near food sources. We report that Melipona mandacaia foragers (stingless bees) deposit an odor cue, anal droplets, and a previously undescribed ventro-abdominal odor on food sources. Surprisingly, foragers deposited attractive odor marks on good food sources to which they recruited and on poor food sources to which they did not recruit. Foragers left the most anal droplets on dilute food sources to which they did not recruit (1.25-M sucrose solution), yet returning foragers were attracted to anal droplets obtained on poor food sources and presented in bioassays. Foragers were attracted to ventro-abdominal odors obtained on good food sources (2.5-M sucrose solution). Chemical extractions suggest that odor marks contain attractive polar compounds. We also provide the first detailed description of forager waggling and spinning behavior on poor and good food sources. Waggling may be a method of dispersing anal droplets and spinning may help foragers learn local landmarks.

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 100 m from the nest).

Foragers of the stingless bee Meliponapanamica can communicate the location of a good food source to nestmates and evidently communicate part of this information inside the nest. However there is no careful description of within-nest recruitment behavior for this species or for any other stingless bee. Therefore the goal of this paper is to provide a detailed description of the behaviors of recruiting M. panamica foragers within the nest. A recruiting forager enters the nest, begins producing pulsed sounds as food-unloading bees collect her food (unloading phase), and then performs a dance by rapidly executing clockwise and counterclockwise turns while continuing to produce sound pulses (dance phase). To investigate whether directional information is encoded in the dance, I alternately recorded the behavior of foragers trained to two food sources, each 175 m from the colony but in opposite directions (north and south). I examined the following parameters and found no differences between the dances of foragers feeding in opposite directions: (1) order of clockwise and counterclockwise turns, (2) turn direction, (3) angular start position, (4) angular stop position, (5) turn magnitude, and (6) turn angular velocity. Foragers recruiting for a rich food source (2.5 M) initially unloaded food with their bodies oriented 180° from the entrance. They began turns at random orientations, but tended to end these turns facing the nest entrance (0°). Dancers for poor food sources (1.0 M sucrose solution) turned at significantly lower velocities than dancers for good food sources (2.5 M sucrose solution), and exhibited random initial, start-turn, and stop-turn orientations. Throughout her stay inside the nest, the recruiting forager produced sounds. During sound production, her folded wings vibrated dorsoventrally over her abdomen and she attracted the attention of follower bees who positioned their antennae closely around her body. Foragers recruiting for 1.0 M and 2.5 M food sources attracted the same number of food-unloading bees, but 1.0 M recruiters attracted significantly fewer followers around their abdomens.

Melipona panamica foragers can deposit a scent beacon that influences the orientation of foragers near a food source. In misdirection experiments, new- comers (bees from the same colony as trained foragers) consistently preferred the feeder at which trained for- agers had fed (training feeder) over an identical feeder at which bees had never fed (control feeder) even when the training feeder was placed at a site where experienced foragers had never foraged. Through similar misdirec- tion experiments, the eAective radius of the scent beacon was determined to be greater than 6 and less than 12 m. Foragers may deposit this beacon during a sequence of departure behaviors performed at the feeder. Prior to leaving the feeder with a load of sugar solution, bees tended to perform the following sequence of behaviors: (1) spinning, (2) grooming, (3) abdomen dragging, (4) excreting anal droplets, and (5) producing sounds, al- though not all behaviors were performed prior to each departure or at all sucrose concentrations (0.5-2.5 M). As sucrose concentration increased, the number of newcomers significantly increased, and the number of experienced foragers producing sounds and spinning on the feeder increased. The exact source of the scent bea- con remains a mystery. However, three important sources have been excluded. When choosing between identical paired feeders, foragers were not attracted to the feeders with (1) anal droplets, (2) extracts of sucrose solution at which foragers had fed, or (3) mandibular gland extracts. They were indiAerent to the first two preparations and exhibited only typical alarm behavior towards the mandibular gland (MG) extract: they ori- ented towards the feeder with MG extract but consis- tently landed on the feeder with no MG extract. Other authors have suggested that Melipona foragers deposit anal droplets to attract recruits, however the frequency of anal droplet production and the mass of anal droplets produced by M. panamica foragers are negatively cor- related with sucrose concentration. Thus the scent bea- con is evidently not deposited with anal droplets, infused into the feeder solution, or produced by mandibular glands.

Received: 21 March 1997 /Accepted after revision: 30 August 1997 Abstract This study explores the meaning and func- tional design of a modulatory communication signal, the honey bee shaking signal, by addressing five questions: (I) who shakes, (II) when do they shake, (III) where do they shake, (IV) how do receivers respond to shaking, and (V) what conditions trigger shaking. Several results confirm the work of Schneider (1987) and Schneider et al. (1986a): (I) most shakers were foragers (at least 83%); (II) shaking exhibited a consistent temporal pattern with bees producing the most signals in the morning (0810- 1150 hours) just prior to a peak in waggle dancing ac- tivity; and (IV) bees moved faster (by 75%) after re- ceiving a shaking signal. However, this study diAers from previous work by providing a long-term, temporal, spatial, and vector analysis of individual shaker behav- ior. (III) Bees producing shaking signals walked and delivered signals in all areas of the hive, but produced the most shaking signals directly above the waggle dance floor. (IV) Bees responded to the signal by changing their direction of movement. Prior to receiving a signal, bees selected from the waggle dance floor moved, on average, towards the hive exit. After receiving a signal, some bees continued moving towards the exit but others moved directly away from the exit. During equivalent obser- vation periods, non-shaken bees exhibited a strong ten- dency to move towards the hive exit. (V) Renewed for- aging activity after food dearth triggered shaking signals, and, the level of shaking is positively correlated with the duration of food dearth. However, shaking signal levels also increased in the morning before foraging had begun and in the late afternoon after foraging had ceased. This spontaneous afternoon peak has not previously been reported. The shaking signal consequently appears to convey the general message ''reallocate labor to diAerent activities'' with receiver context specifying a more pre- cise meaning. In the context of foraging, the shaking signal appears to activate (and perhaps deactivate) col- ony foraging preparations. The generally weak response elicited by modulatory signals such as the shaking signal may result from a high receiver response threshold which allows the receiver to integrate multiple sources of information and which thereby increases the probability that receiver actions will be appropriate to colony needs.

The stop signal of honey bees has long been regarded as a vibrational begging signal produced by dance followers to elicit food from waggle dancers (Esch 1964). On the basis of playback experiments and behavioral analysis, this study presents the following evidence for a different signal function. Stop signals (1) can be produced by tremble dancers, dance followers, and waggle dancers; (2) rarely elicit trophallaxis; and (3) evidently cause waggle dancers to leave the dance floor. Subsequent work by Kirchner (submitted) using vibrational playback experiments confirms the latter observation. When the colony's food storers are temporarily overwhelmed by a large nectar influx, returning foragers will search for prolonged periods before unloading food and consequently begin to tremble dance (Seeley 1992). In this study, tremble dancers were the major producer of stop signals on the dance floor. The stop signal may thus retard recruitment until balance is restored.

Polarized odor-trail communication, in which a receiver can orient towards the correct endpoint from within the trail, is documented in relatively few animals and is poorly understood, although such directionality could significantly enhance resource localization. Among animals, stingless bees exhibit the unique behavior of depositing long substrate-borne odor trails that assist the orientation of flying nestmates to a specific three-dimensional food location. However, relatively little is known about the spatial structure of such odor trails, particularly vertical trails, and whether these trails are polarized to indicate the correct terminus. We show that a stingless bee, Trigona spinipes, can rapidly recruit nestmates in large bursts to a food source at a specific distance, direction, and height. In conjunction with a major recruitment burst, foragers deposited odor marks that attracted nestmates for up to 20 min. Surprisingly, these odor marks formed a short odor trail instead of a complete odor trail extending from the feeder to the nest (the classic description of a meliponine odor trail). The length of the odor trails varied between different feeder locations with different colonies, from a minimum of 3 m to a maximum of 29 m. The odor marks formed a polarized trail that newcomers followed to the end with the most concentrated odor marks (the feeder), even when the entire odor trail was rotated 180° and clean test feeders were set out at locations that foragers had never previously fed at. Thus locale odor or the potential communication of food location inside the nest do not account for the ability of newcomers to find the correct terminus. This result provides the first strong evidence for odor-trail polarization in social insects.

Scent marking of profitable food sources improves foraging efficiency and helps social bees meet colony demands for unpredictable floral resources (Giurfa and Nunez, 1992). Sophisticated marking has evolved in the stingless bees (Apidae, Meliponini); several genera recruit nestmates to profitable food sources with scent signals (reviewed in Nieh, 2004). Scent cues such as “footprints” (Wilms and Eltz, 2008) can also facilitate navigation and orientation to rewarding parts of food patches. Scent marks may improve colonies’ competitive ability, especially in the tropics, where social bee abundance and diversity are high. We assessed scent mark use by the stingless bee Melipona quadrifasciata. This species poorly communicates to nestmates the location of rich food sources (Jarau et al., 2000), thus could benefit from within-patch orientation information provided by attractive odor marks. However, its ability to deposit and use fieldbased information is not known. We studied four Melipona quadrifasciata anthidioides colonies at the Universidade de Sao Paulo, Ribeirao Preto in July 2007, and July– August 2008, using feeder choice tests (see, for example, Hrncir et al., 2004). To begin a trial, we allowed foragers trained to feed on 1.5 M sucrose solution to recruit 15 nestmates not previously used in the experiment. The 15 bees freely fed at a “visited” feeder for 10 min, during which we counted the number of visits. Next, we aspirated all bees and replaced the original apparatus with the visited and clean feeders on clean tripods, separated by 30 cm.

The regulation of protein collection through pollen foraging plays an important role in pollination and in the life of bee colonies that adjust their foraging to natural variation in pollen protein quality and temporal availability. Bumble bees occupy a wide range of habitats from the Nearctic to the Tropics in which they play an important role as pollinators. However, little is known about how a bumble bee colony regulates pollen collection. We manipulated protein quality and colony pollen stores in lab-reared colonies of the native North American bumble bee, Bombus impatiens. We debut evidence that bumble bee colony foraging levels and pollen storage behavior are tuned to the protein quality (range tested: 17–30% protein by dry mass) of pollen collected by foragers and to the amount of stored pollen inside the colony. Pollen foraging levels (number of bees exiting the nest) significantly increased by 55%, and the frequency with which foragers stored pollen in pots significantly increased by 233% for pollen with higher compared to lower protein quality. The number of foragers exiting the nest significantly decreased (by 28%) when we added one pollen load equivalent each 5 min to already high intranidal pollen stores. In addition, pollen odor pumped into the nest is sufficient to increase the number of exiting foragers by 27%. Foragers directly inspected pollen pots at a constant rate over 24 h, presumably to assess pollen levels. Thus, pollen stores can act as an information center regulating colony-level foraging according to pollen protein quality and colony need.