Nectar Foragers Research Articles

Floral scents affect the distribution of hive bees around dancers

Floral scents are important information cues used to organize foraging-related tasks in honeybees. The waggle dance, apart from encoding spatial information about food sources, might facilitate the transfer of olfactory information by increasing the dissipation of volatiles brought back by successful foragers. By assuming that food scents are more intensive on specific body parts of returning foragers, i.e., the posterior legs of pollen foragers and mouthparts of nectar foragers, we quantified the interactions between hive mates and foragers during dances advertising different types of food sources. For natural sources, a higher proportion of hive mates contacted the hind legs of pollen dancers (where the pollen loads were located) with their heads compared to non-pollen dancers. On the other hand, the proportion of head-to-head contacts was higher for non-pollen foragers during the waggle runs. When the food scent was manipulated, dancers collecting scented sugar solution had a higher proportion of head-to-head contacts and a lower proportion around their hind legs compared to dancers collecting unscented solution. The presence of food odors did not affect in-hive behaviors of dancers, but it increased the number of trophallaxes in-between waggle runs (i.e., during circle phases). These results suggest that the honeybee dance facilitates the olfactory information transfer between incoming foragers and hive mates, and we propose that excitatory displays in other social insect species serve the same purpose. While recent empirical and theoretical findings suggested that the colony level foraging benefits of the spatial information encoded in the waggle dance vary seasonally and with habitats, the role of the dance as a compound signal not only indicating the presence of a profitable resource but also amplifying the information transfer regarding floral odors may be important under any ecological circumstances.

Scaling of Nectar Foraging in Orchid Bees

Morphology influences the rate at which foraging bees visit nectar flowers, the quantity of nectar they must consume to fuel their activities, and, consequently, the profitability of flower species. Because feeding time is a major determinant of visitation rate, I used a biomechanical model to examine how energy intake rate (E) varies with sucrose concentration, body mass (M), and proboscis length in orchid bees (Apidae: Euglossini). Under geometric scaling, the optimal sugar concentration (Smax) should be largely independent of body size, and E proportional to M1.0. In a comparative study of 30 orchid bee species ranging from 50 to 800 mg, Smax fell between 35% and 40% w/w, but E proportional to M0.54, significantly less than model predictions. Proboscis length and radius scale geometrically with body mass, but proboscis length exhibits substantial size-independent variation, particularly in small bees. One cost of a long proboscis is a reduction in both E and Smax in accordance with the scaling model. This finding highlights a difference between the lapping mechanism used by bumblebees and the suction mechanism used by orchid bees. A field study confirms that orchid bees harvest nectars with between 34% and 42% sucrose, independent of body size.

Foraging loads of stingless bees and utilisation of stored nectar for pollen harvesting

We compared nectar, pollen and resin loads of individual workers among colonies from six Trigona species in Sabah, Borneo. Individual bees rarely collected large amounts of both nectar and pollen during the same foraging trip. Instead, comparison of crop contents across departing, flower-visiting, and returning bees suggests that pollen-collecting workers often carried highly concentrated nectar in their crop upon nest departure. During their foraging trip, this crop nectar volume decreased progressively until crops were largely empty when they returned to their nest. Individually marked pollen foragers carried highly concentrated nectar when they left their nest, while crops and corbiculae from marked nectar foragers were empty upon departure. We suggest that a large proportion of previously stored and highly concentrated nectar may be required for pollen adhesion to corbiculae and/or serve as fuel during foraging on nectar-poor flowers.

Scaling of Nectar Foraging in Orchid Bees

Scaling of Nectar Foraging in Orchid Bees

Honeybees learn floral odors while receiving nectar from foragers within the hive

Recent studies showed that nectar odors brought back by honeybee foragers can be learned associatively inside the hive. In the present study, we focused on the learning abilities of bees, which directly interact via trophallaxis with the incoming nectar foragers: the workers that perform nectar-receiving tasks inside the hive. Workers that have received food directly from foragers coming back from a feeder offering either unscented or scented sugar solution [phenylacetaldehyde (PHE) or nonanal diluted] were captured from two observational hives, and their olfactory memories were tested using the proboscis extension response paradigm. Bees that have received scented solution from incoming foragers showed significantly increased response frequencies for the corresponding solution odor in comparison with those that have received unscented solution. No differences in the response frequencies were found between food odors and colonies. The results indicate that first-order receivers learn via trophallaxis the association between the scent and the sugar solution transferred by incoming foragers. The implications of these results should be considered at three levels: the operational cohesion of bees involved in foraging-related tasks, the information propagation inside the hive related to the floral type exploited, and the putative effect of these memories on future preferences for resources.

Communication in ants

Research shows that ants, and also honeybees and other species of social insects, use several pheromones or other signals in organizing their foraging system. Two important and connected questions, therefore, are to determine why multiple signals are needed and how they work together. Some progress has been made in the honeybee, where four dances and a pheromone are known to be involved. The role of most of these signals is known. The waggle dance directs foragers to food and recruits them to foraging, the vibratory dance prepares foragers for work by causing them to move into the dance floor area where returning foragers make waggle dances, and the tremble dance recruits additional workers to the task of unloading nectar foragers. But what is not known is precisely how they work together and why five signals (and maybe more) are needed. Why not four?One possibility is that some of these signals are fine tuning. Multiple signals may be needed because of inherent limitations in the signals used. For example, the short-lived attractive and repellent trail pheromones used by Pharaoh's ants can direct foragers to the rewarding branch at a trail bifurcation but a single one of these pheromones can only direct about 75% to the rewarding branch. Perhaps the presence of two pheromones can increase this to 90%.We also need to understand communication mechanisms in relation to the foraging method. The solid substrate upon which ants walk from nest to food is suitable for depositing trail pheromones to guide nestmates. A trail pheromone is obviously less useful for flying social insects, such as honeybees. However, some stingless bees do mark routes to food with pheromone, which they deposit on vegetation as discrete beacons rather than a continuous trail. The use of a trail pheromone means channels of communication may be continuously open for ants, because they are capable of a continual, reactive exchange of information with nestmates whilst foraging. This is in marked contrast with the honeybee, where the signals used to organize foraging are communicated in the nest. Foraging is a dynamic process and an important role of communication is to recruit or direct nestmates rapidly to a food source. But the need to do more than this, for example to retain a longer term memory, may require additional pheromones or signals.The multiple signals used in social insect communication provide shared information and enable the colony (or system) to be more responsive or better regulated, so that it functions better. Similar complexity is found at other biological levels, such as cell signalling pathways, where positive and negative feedback provide the capacity for control at multiple levels and enable greater flexibility in system responsiveness. A major interdisciplinary challenge in modern biology is to understand how complex adaptive systems function, and how they function robustly yet flexibly. One goal in this research is to determine if there are any general principles underlying adaptive biological systems. The focus of this research, and the funding, is usually directed at the organismal level or below, particularly cells in a multicellular organism, or molecules within cells. Insect societies provide another level of organization for comparison.

The dioecious, sphingophilous species Citharexylum myrianthum (Verbenaceae): Pollination and visitor diversity

Citharexylum myrianthum is an example of cryptic dioecy in morphologically perfect flowers. Flowers are small, tubular, white-colored, and crepuscular, with a sweet, pleasant scent and occur in raceme-like inflorescences. Functionally, male flowers have a less developed ovary and females have anthers lacking pollen. They are pollinated by five species of Sphingidae. The low fruit set under natural conditions, compared with the very high fruit set after hand-pollination, apart from other possible factors, suggests that pollen flow is limited mainly by pollinators. The overabundance of nectar provided by C. myrianthum flowers attracts a large number of opportunistic nectar foragers in the morning. Hummingbirds, the most frequent visitors, are nectar thieves and display territorialism, being aggressive even to Passeriformes. Despite its visitor diversity C. myrianthum is pollinated by sphingids, and in this sense this species is a specialist rather than a generalist.

Foraging by Male and Female Solitary Bees with Implications for Pollination

Both male and female solitary bees visit flowers for rewards. Sex related differences in foraging efficiency may also affect their probability to act as pollinators. In some major genera of solitary bees, males can be identified from a distance enabling a comparative foraging-behavior study. We have simultaneously examined nectar foraging of males and females of three bee species on five plant species in northern Israel. Males and females harvested equal nectar amounts but males spent less time in each flower increasing their foraging efficiency at this scale. The overall average visit frequencies of females and males was 27.2 and 21.6 visits per flower per minute respectively. Females flew shorter distances increasing their visit frequency, relative foraging efficiency and their probability to pollinate. The proportion of conspecific pollen was higher on females, indicating higher floral constancy and pollination probability. The longer flights of males increase their probability to cross-pollinate. Our results indicate that female solitary bees are more efficient foragers; females seem also to be more efficient pollinators but males contribute more to long-distance pollen flow.

Unlike nectar foragers, honeybee drones (Apis mellifera) are not able to utilize starch as fuel for flight

Des butineuses de nectar, prelevees lors de leur arrivee sur la source de nourriture, et des mâles d'abeilles .(Apis mellifera L.), definis par leur âge et leur comportement, ont recu en nourrissement diverses solutions de glucose et de glucose additionne d'amidon, puis ont ete places dans un carrousel de vol (Hrassnigg et Crailsheim, 1999). Apres leur capture les insectes ont d'abord ete soumis a un premier « vol de nettoyage » i.e. sans nourrissement, au cours duquel ils devaient utiliser toutes leurs reserves alimentaires. On leur a fourni ensuite une solution nutritive donnee et, apres une periode de repos de 6 a 8 min, ils ont ete incites a accomplir un autre vol. Pour une meme quantite de nourriture, les mâles ont vole moins longtemps et moins loin que les ouvrieres. mais leur vitesse de vol etait plus elevee (Fig. 2a, b). Les butineuses ont augmente leur temps de vol de 30,2 % lorsqu'elles ont recu une solution de glucose et d'amidon (10 μL, glucose 2 M + l'equivalent de glucose 1 M sous forme d'amylose) a la place d'une solution simple de glucose (10 μL, 2 M). L'augmentation du temps et de la distance de vol a ete a peu pres semblable avec une solution de glucose 3 M ou une autre solution de glucose et d'amidon (glucose 2,5 M et l'equivalent de glucose 0,5 M) comme nourrissement. Ni la duree, ni la distance de vol n'ont ete augmentees par l'addition d'amidon au sirop de nourrissement, que ce soit chez les mâles de poids normal (213,57 ± 15,37 mg, n = 28) ou chez les mâles nains (135,13 ± 16,94 mg, n = 7) (Fig. 1). Il en a ete de meme avec une solution de miel et d'amidon, qui correspondait en energie a une solution de glucose et d'amidon (2 + 1 M) et contenait l'amylase du miel, qui degrade l'amidon. Le temps de vol n'a pas ete non plus augmente lorsque les vols ont ete repetes avec les memes mâles suite a un nourrissement d'amidon (Tab. I), bien que dans ce cas l'amidon ait pu sejourner plus longtemps dans le tube digestif et ait pu etre digere sur une periode plus longue. La capacite des ouvrieres a digerer les polysaccharides est une donnee importante pour la pratique apicole en liaison avec le nourrissement au sirop. Pour les abeilles qui hivernent les oligosacharides produits par l'hydrolyse de l'amidon doivent avoir une action negative. Il decoule de nos resultats qu'au moins les butineuses de nectar possedent les enzymes pour degrader efficacement l'amidon soluble en glucose. Le fait que les mâles ne soient pas capables, contrairement aux ouvrieres, de degrader rapidement l'amylose, souligne le role central des ouvrieres comme elaboreuses de nourriture au sein de la colonie.

Effect of elevated atmospheric CO2 on oviposition behavior in Manduca sexta moths

AbstractMoths can detect changes in environmental carbon dioxide (CO2) with extremely high sensitivity, but the role of CO2 in the biology of these and other insects is not well understood. Although CO2 has been demonstrated to influence egg‐laying (oviposition) behavior of the pyralid moth Cactoblastis cactorum and nectar foraging of the sphingid moth Manduca sexta, information about the generalized role of CO2 in the behavioral biology of these species is lacking. Comparative data are necessary to properly assess how the behaviors of different species may be modified by steadily rising levels of greenhouse gases in the environment. Experiments carried out in Biosphere 2 addressed whether changes in ambient CO2 levels play a role in the oviposition behaviors of M. sexta moths. In the first series of experiments, oviposition was measured inside a flight cage with different levels of nearly ambient or elevated CO2 (400, 800 or 1200 ppm). For each concentration, hostplants used as oviposition sites were grown from seed at a CO2 level that matched the environment inside the flight cage. Under homogenous levels of CO2, we observed no significant difference in oviposition behavior at the concentrations tested. In a second series of experiments, two groups of hostplants, each surrounded by a mini free‐air CO2 enrichment (FACE) ring, were assembled inside a flight cage. In this choice test, a dynamic plume of artificially high CO2 was generated around one group of test plants, while ambient CO2 was released around the second (control) group. After eggs were counted on both plant groups, M. sexta females showed a small preference for ovipositing on the control plants. Therefore, in contrast to C. cactorum females tested under similar dynamic flow conditions, M. sexta female oviposition was not strongly inhibited by elevated CO2. To investigate this phenomenon further, we used electrophysiological recording and found that the CO2 receptor cells in M. sexta, unlike those in C. cactorum, are not readily affected by elevated levels of ambient CO2. These findings therefore suggest that elevated background levels of CO2 affect the physiology of the CO2 detection system of M. sexta to a lesser extent than that of C. cactorum, and this correlates well with the observed differences in oviposition behavior between the two species under elevated levels of environmental CO2. Hostplants of C. cactorum are crassulacean acid metabolism plants that generate nocturnal CO2 sinks on the cladode surfaces, whereas, M. sexta hostplants are nocturnal sources of respiratory CO2. We hypothesize that the abrupt and continuing increase in global ambient CO2 levels will differentially alter the behavior and physiology of moths that use CO2 sinks and sources as sensory cues to find hostplants.

Nectar foraging behaviour is affected by ant body size in Camponotus mus

The nectivorous ant Camponotus mus shows a broad size variation within the worker caste. Large ants can ingest faster and larger loads than small ones. Differences in physiological abilities in fluid ingestion due to the insect size could be related to differences in decision-making according to ant size during nectar foraging. Sucrose solutions of different levels of sugar concentration (30% or 60%w/w), viscosity (high or low) or flow rate (ad libitum or 1 μl/min) were offered in combination to analyse the behavioural responses to each of these properties separately. Differences were found depending on ant body size and the property compared. A regulated flow produced smaller crop loads for medium and large ants compared to the same solution given ad libitum. All foragers remained longer times feeding at the regulated flow source but larger ants often made longer interruptions. When sugar concentration was constant but viscosity was high, only large ants increased feeding time. Constant viscosity with different sugar concentration determined longer feeding time and bigger loads for the most concentrated solution for small but not for large ants. Small ants reached similar crop loads in a variety of conditions while large ants did not. These differences could be evidence of a possible specialization for nectar foraging based on ant body size.

Floral biology and behavior of Africanized honeybees Apis mellifera in soybean (Glycine max L. Merril)

This research was carried out to evaluate the pollination by Africanized honeybees Apis mellifera, the floral biology and to observe the hoarding behavior in the soybean flowers (Glycine max Merril), var. BRS-133. The treatments were constituted of demarcated areas for free visitation of insects, covered areas by cages with a honeybee colony (A. mellifera) and also covered areas by cage without insects visitation. All areas had 24 m² (4m x 6m). The soybean flowers stayed open for a larger time (82.82 ± 3.48 hours) in covered area without honeybees. The stigma of the flowers was also more receptive (P=0.0021) in covered area without honeybees (87.3 ± 33.0%) and at 10:42 o'clock was the schedule of greater receptivity. The pollen stayed viable in all treatments, the average was 99.60 ± 0.02%, which did not present differences among treatments. The percentage of abortion of the flowers was 82.91% in covered area without honeybees, this result was superior (P=0.0002) to the 52.66% and 53.95% of the treatments uncovered and covered with honeybees, respectively. Honeybees were responsible for 87.7% of the pollination accomplished by the insects. The medium amounts of total sugar and glucose measured in the nectar of the flowers were, 14.33 ± 0.96 mg/flower and 3.61 ± 0.36 mg/ flower, respectively, not showing differences (P<0.05) among the treatments. The total solids, measured through the manual refratometer were 21.33 ± 0.22% in uncovered area and 22.33 ± 0.38% in covered with honeybees and differed to each other (P=0.0001). The honeybees were the most frequent insect (95.18%). Other observed insects were the Lepidoptera with 3.51% and other bees with 1.32%, in uncovered area. Honeybees visited 2.24 flowers on average in uncovered area and 1.58 in covered with honeybees and presented behavior for nectar hoarding and hoarding nectar/pollen in this period. In uncovered area the time of nectar hoarding was 2.55 ± 0.07 seconds, this time was smaller (P=0.0039) than 2.87 ± 0.08 seconds observed in covered area with honeybees. The behavior for the hoarding type observed in honeybees foraging the soybean flowers, through the content of its honey stomach and pollen loads of its pollen basket showed that the nectar forager did not show a pattern for the nectar collection, but for the pollen collection the schedule of pollen peak of the forager was at 11:36 o'clock. The soybean flowers showed alteration in floral biology when exposed to honeybees.

Locomotion and the pollen hoarding behavioral syndrome of the honeybee (Apis mellifera L.)

Honeybees selected for the colony level phenotype of storing large quantities of pollen (pollen hoarding) in the nest exhibit greater walking activity than those selected against pollen hoarding. In this study, we use a simple walking assay to demonstrate that walking activity increases with the proportion of high pollen-hoarding alleles in pure and backcrossed strains of bees (high-strain bees > offspring generated from a high backcross > offspring generated from a low backcross > low-strain bees). The trait is heritable but is not associated with markers linked to three quantitative trait loci (QTL) mapped for their effects on pollen hoarding with demonstrated pleiotropic effects on pollen and nectar foraging and learning behavior. However, locomotion in non-selected bees is correlated with responsiveness to sucrose, a trait that correlates with foraging and learning behavior. We propose that pollen-hoarding behavior involves a syndrome of behavioral traits with complex genetic and regulatory architectures that span sensory sensitivity, foraging behavior, and learning. We propose that locomotor activity is the component of this syndrome and reflects the early maturation of the bees that become pollen foragers.

Trophallaxis within the dancing context: a behavioral and thermographic analysis in honeybees (Apis mellifera)

Honeybee workers that follow a dancing bee within the hive may contact its mouthparts to receive a food sample. It is currently unknown which proportion of begging bees actually receive food samples via trophallaxis from a dancer. We combined behavioral and thermographic recordings to analyze trophallactic behavior considering the informational context in which these interactions occurred. Dance followers engaged in shorter oral contacts and achieved a lower proportion of effective receptions (26%) than non-followers (58%). These results show that oral contacts often occur between dancers and followers, but their brief duration suggests that followers may just probe the incoming nectar. However, short contacts might allow unemployed nectar foragers either to taste or smell (or both) the solution exposed between the dancer's mandibles, which may contribute to the acquisition of information involved in the decision to visit that food source.

Synergy between visual and olfactory cues in nectar feeding by wild hawkmoths, Manduca sexta

We performed field experiments to measure the relative importance of olfactory and visual cues in nectar foraging by wild tobacco hornworm moths, Manduca sexta (Lepidoptera, Sphingidae) in the Sonoran Desert of Arizona, U.S.A. We manipulated flowers of sacred Datura (Datura wrightii; Solanaceae) to experimentally decouple floral scent from visual display and presented these cues to free-flying moths in mixed and homogeneous arrays. Moths did not feed from cloth-bagged fragrant flowers lacking strong visual contrast, nor did they feed from paper model flowers lacking plant odours. Unexpectedly, moths fed from paper model flowers that were associated solely with vegetative odours, albeit at lower levels than when floral scent was present. Subsequent experiments revealed that the combination of floral and vegetative odours did not incrementally increase nectar feeding and that floral scent without vegetation was sufficient to elicit feeding when paper flowers were present. Thus, wild M. sexta in our study did not show generalized feeding responses to natural or artificial flowers with single sensory stimuli; like naïve laboratory-reared moths, they required a combination of visual and olfactory cues. However, given the prior foraging experience of our study population on Datura flowers, their lack of generalized feeding responses may reflect a learned preference for the full complement of floral cues, rather than the persistence of innate sensory constraints. Future efforts to distinguish between these hypotheses should focus on whether M. sexta can be conditioned to associate nectar with visual cues alone, and whether moths that feed ad libitum from nectar-rich plants learn floral attributes as a search image or generalize to single-modality stimuli.

Foraging behavior and pollinating effectiveness of Osmia cornuta (Hymenoptera: Megachilidae) and Apis mellifera (Hymenoptera: Apidae) on ?Comice? pear

We studied the pollinating effectiveness of Osmia cornuta and Apis mellifera on 'Comice' pear. Osmia cornuta visited more flowers per minute (13.8) than A. mellifera (7.1-9.8). Both species visited similar numbers of flowers per tree (6.7-7.9), and switched rows with similar frequency (4.0-7.9%). Rate of stigma contact was 98.7% for O. cornuta, 51.8% for A. mellifera pollen-nectar foragers, and 19.0% for A. mellifera nectar foragers. Fruit-set in flowers visited once was 28.9, 29.3, and 12.9%, respectively. Seed- set was similar (7-8 seeds per fruit) in all three types of flowers. Osmia cornuta females provisioned their nests with 94.4% pear pollen. Stepwise multiple regression showed that fruitlet-set across the orchard was mostly related to tree size (trees with fewer flowers set more fruit per flower) (β = -0.64; P <0 .001), whereas seed-set at harvest was best explained by O. cornuta (β = 0.47; P < 0.005) and A. mellifera (β = 0.35; P < 0.05) spatial distribution. Osmia cornuta / Apis mellifera / pollinating effectiveness / pear pollination

The communal crop: modulation of sucrose response thresholds of pre-foraging honey bees with incoming nectar quality

We examined whether the quality (concentration) of incoming sucrose solutions returned by foraging honey bees affected the response thresholds of pre-foraging members of the colony. Six pairs of colonies were given ad libitum access to sucrose solution feeders. A colony from each pair was switched from 20–50% sugar concentration feeders while the other continued to have access to 20% sucrose feeders. Proboscis extension response (PER) scores to an increasing series of sucrose concentrations were significantly higher in pre-foragers of colonies foraging on 20% sucrose throughout compared to pre-foragers in colonies where foraging was switched to 50% sucrose. Although all colonies had honey stores, the concentration of sugar solution in non-foraging bees’ crops were significantly lower in bees from colonies foraging on 20% sucrose compared to those from colonies foraging on 50% sucrose. Because response thresholds to sugar of young bees were modulated by the concentration of sucrose solution returned to colonies, we repeated the 2000 study of Pankiw and Page that potentially confounded baseline response thresholds with modulated scores due to experience in the colony. Here, we examined PER scores to sucrose in bees within 6 h of emergence, prior to feeding experience, and their forage choice 2 to 3 weeks later. Pollen foragers had higher PER scores as newly emerged bees compared to bees that eventually became nectar foragers. These results confirm those of the 2000 study by Pankiw and Page. Combined, these experiments demonstrate that variation in pre-forager sucrose response thresholds are established prior to emerging as adults but may be modulated by incoming resources later on. Whether this modulation has long-term effects on foraging behavior is unknown but modulation has short-term effects and the potential to act as a means of communication among all bees in the colony.

Multiple unloadings by nectar foragers in honey bees: a matter of information improvement or crop fullness?

When a honey bee forager returns to her hive and unloads nectar, she sometimes transfers her entire load to one bee, but other times she makes a series of unloadings to several bees. One intriguing hypothesis for why foragers make multiple unloadings is the Information Improvement hypothesis: multiple unloadings improve a forager’s estimate of the difficulty in finding a receiver bee, and thus of the allocation of labor between nectar collecting and nectar processing. In this paper, we discuss a possible weakness in the empirical evidence in support of the Information Improvement hypothesis. We also present a competing hypothesis, the Crop Fullness hypothesis: multiple unloadings arise from a mismatch between the amount of nectar a forager has to unload and the amount of nectar a receiver can imbibe. Finally, we test the two hypotheses by checking their predictions regarding the conditions under which multiple unloadings occur and which bee (forager or receiver) breaks off the first unloading when a forager makes multiple unloadings. We find that multiple unloadings are common only at times of high nectar influx and that most often it is the receiver, not the forager, who breaks off the first unloading. We argue that both of these findings are contradictory to the Information Improvement hypothesis but are consistent with the Crop Fullness hypothesis. Furthermore, we relate our findings to a recent theoretical study (Gregson et al., 2003) which shows, by means of a simulation model, that the level of multiple unloadings observed can be accounted for by a mismatch between the crop loads of foragers and the crop capacities of receiver bees. We combine our measurements with the Gregson et al. model to identify the rule used by receiver bees in deciding when to stop receiving more nectar. We conclude that receivers make this decision during the course of an unloading, not after completing an unloading. Finally, with this conclusion in hand, we test the Gregson et al. model by comparing predictions and observations on how full receivers are when they decide to break off an unloading. We find a remarkable agreement (prediction: 60%, observation: 52–59%), in strong support of the model.

Colour learning in two behavioural contexts: how much can a butterfly keep in mind?

Here we examine the ability of butterflies to learn colour cues in two different behavioural contexts, nectar foraging and oviposition, more or less simultaneously. We first trained female Battus philenor (Papilionidae) butterflies to associate a given colour with the presence of host plant leaf extract and assayed their colour preference; we then trained a subset of these butterflies to associate a second colour with the presence of sucrose solution and assayed colour preference once more. When offered an array of four unscented and unrewarding coloured models, ‘single-trained’ butterflies consistently alighted most frequently on their oviposition training colour. Green-trained butterflies landed on nontrained colours only about 4% of the time, while butterflies trained to red, yellow or blue made about 23% of their landings on nontrained colours; of those nontrained landings, most were on green. The majority of ‘dual-trained’ butterflies made the greatest number of visits to both training colours in the appropriate behavioural context; that is, they probed the models of their sucrose-associated colour and alighted on the models of their oviposition-associated colour. Landings or probes on nontrained colours in one context were consistently biased towards what was learned in the alternative context, suggesting an information–processing constraint in the butterflies. This paper provides a clear demonstration that butterflies can learn in two behavioural contexts within a short span of time. A capacity for such dual conditioning presumably permits female butterflies to forage effectively for egg-laying sites and nectar resources even when those activities are intermingled in time. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Worker piping in honey bees (Apis mellifera): the behavior of piping nectar foragers

This study investigates the brief piping signals ("stop signals") of honey bee workers by exploring the context in which worker piping occurs and the identity and behavior of piping workers. Piping was stimulated reliably by promoting a colony's nectar foraging activity, demonstrating a causal connection between worker piping and nectar foraging. Comparison of the behavior of piping versus non-piping nectar foragers revealed many differences, e.g., piping nectar foragers spent more time in the hive, started to dance earlier, spent more time dancing, and spent less time on the dance floor. Most piping signals (approximately 99%) were produced by tremble dancers, yet not all (approximately 48%) tremble dancers piped, suggesting that the short piping signal and the tremble dance have related, but not identical, functions in the nectar foraging communication system. Our observations of the location and behavior of piping tremble dancers suggest that the brief piping signal may (1) retard recruitment to a low-quality food source, and (2) help to enhance the recruitment success of the tremble dance.