Spatial foraging patterns of the African honey bee,Apis mellifera scutellata

Recruitment patterns were investigated for the African honey bee in the Okavango River Delta, Botswana. The waggle dances of two observation colonies maintained in the field were monitored and used to construct maps of daily recruitment activity. These maps revealed that the African colonies frequently adjusted the allocation of recruits among food patches, recruited for 16–17 different food sites/day over areas of 55–80 km ² ,and concentrated the majority of recruitment within 1 km of the hives (median foraging distances for the two colonies were 295 and 563 m). In both colonies pollen foragers were more abundant than nectar foragers, and pollen sources indicated by waggle dancers were significantly closer to the hives than nectar sources. Compared to the recruitment patterns of temperate climate colonies, the African colonies had smaller recruitment areas, smaller mean recruitment distances, and a greater emphasis on pollen foraging. These differences may be related to the contrasting survival strategies followed by tropical-versus temperate-climate honey bees.     

The waggle dance of the honey bee: Which bees following a dancer successfully acquire the information?

During the waggle dance of the honeybee, the dancer is able to tell her nestmates the distance and direction to a rich food source (Frisch, 1967). Little is known about how waggle dance followers are able to read the waggle dance in the darkness of a hive. Initial observations showed that not all of the bees that appear to be dance followers behave the same. Some bees maneuver themselves behind the dancer, while others do not. The paths of a single dancer, trained to an artificial food source, and her followers were traced during the waggle runs. The success of these dance followers was compared to their position relative to the dancer. The results of this study show that during a waggle run a dance follower must position itself within a 30° arc behind the dancer in order to obtain the dance information. The results suggest that bees are using the position of their own bodies to determine direction.     

Do honey bees encode distance information into the wing vibrations of the waggle dance?

An optical technique detected the wing vibration frequency of worker honey bees in an observation hive during the straight run of the waggle dance. Wing oscillation frequencies were recorded from dancing bees after they had visited a feeding station located from 50 to 1600 m from the hive. The bees vibrated their wings more rapidly after they visited nearby stations than when they foraged at more distant feeding stations. For example, the mean frequency of 315 Hz at 50 m dropped to only 207 Hz at 1600 m. Wing vibration frequency appears to be another factor to be added to the elements in the dance known to indicate the distance bees must fly to food sources. These known elements include the duration of the straight run and the number of wagtail movements in the run.     

Nest characteristics and recruitment behavior of absconding colonies of the African honey bee,Apis mellifera scutellata,in Africa

Absconding behavior was investigated in a naturally occurring population of honey bees in the Okavango River Delta, Botswana. Fifty percent of all colonies excavated in the field between October and December had abandoned the nest or were preparing for absconding, suggesting that an absconding season began in the Delta in October or November. However, the factors influencing absconding during this period were unclear, and there were no distinct differences in nest characteristics of the absconding and nonabsconding colonies. Waggle dance activity in observation colonies preparing for absconding was not used to preselect a specific nest site prior to departure. However, in two of the three colonies examined recruitment activity indicated the general direction of colony travel. The distances indicated by these dancers ranged between 6 and 16 km. Since these distances were three to four times greater than those communicated by dancers in nonabsconding colonies, workers from absconding colonies may sample potential forage or nest sites well outside their regular foraging range.     

Inter‐individual variation in honey bee dance intensity correlates with expression of the foraging gene

Individual behavioural differences in responding to the same stimuli is an integral part of division of labour in eusocial insect colonies. Amongst honey bee nectar foragers, individuals strongly differ in their sucrose responsiveness, which correlates with strong differences in behavioural decisions. In this study, we explored whether the mechanisms underlying the regulation of foraging are linked to inter‐individual differences in the waggle dance activity of honey bee foragers. We first quantified the variation in dance activity amongst groups of foragers visiting an artificial feeder filled consecutively with different sucrose concentrations. We then determined, for these foragers, the sucrose responsiveness and the brain expression levels of three genes associated with food search and foraging; the foraging gene Amfor, octopamine receptor gene AmoctαR1 and insulin receptor AmInR‐2. As expected, foragers showed large inter‐individual differences in their dance activity, irrespective of the reward offered at the feeder. The sucrose responsiveness correlated positively with the intensity of the dance activity at the higher reward condition, with the more responsive foragers having a higher intensity of dancing. Out of the three genes tested, Amfor expression significantly correlated with dance activity, with more active dancers having lower expression levels. Our results show that dance and foraging behaviour in honey bees have similar mechanistic underpinnings and supports the hypothesis that the social communication behaviour of honey bees might have evolved by co‐opting behavioural modules involved in food search and foraging in solitary insects.     

Using the waggle dance to determine the spatial ecology of honey bees during commercial crop pollination

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Influence of flight time and flight environment on distance communication by dancing honey bees

Forager honey bees communicate the distance of food sources to nest mates through waggle dances, but how do bees measure these distances? Recent work suggests that bees measure distance flown in terms of the extent of image motion (integrated optic flow) that is experienced during flight. However, it is known that optic flow also regulates the speed of flight. Therefore, the duration of the flight to a destination is likely to co-vary with the optic flow that is experienced en route. This makes it difficult to tease apart the potential roles of flight duration and optic flow as cues in estimating distance flown. Here we examine whether flight duration alone can serve as an indicator of distance. We trained bees to visit feeders at two sites located in optically different environments, but positioned such that the flight durations to the two sites were similar. The distance estimates for the two sites, as reported in the waggle dance, were compared. We found that dances differed significantly between the two sites, even though flight times were similar. Flight time perse was a poor predictor of waggle dance behaviour. We conclude that foraging bees do not simply signal flight time as their measure of distance in the waggle dance; the environment through which they fly plays a dominant role. Received 11 April 2005; revised 16 May 2005; accepted 3 June 2005.     

Implications of variation in worker body size for the honey bee recruitment system

Honey bee scouts seek food from flowers, return to the colony, and may perform a dance used to recruit dance followers to the flowers. Variation in body size of workers may result in the communication of misinformation because some information acquired by the scout and signaled to recruits is affected by body size. I tested two predictions of this hypothesis. (1) Recruitment communication takes place between bees of similar size despite the withincolony size distribution. (2) There is an inverse relationship between the size variation of foraging honey bees (Apis mellifera)and the rate at which nectar is returned to the colony. A positive relationship was found between the size of a dancer and that of its dance followers, which together comprise a dance group. There was less variation in size within dance groups than among groups. These two factors effectively lower the difference in size between signal sender and signal receiver and may enhance the flow of accurate size-dependent information. Also, an inverse relationship between size variation and rate of nectar intake was detected in each of six colonies using partial correlation analysis. This may be due to communication of misinformation when size variance is higher. The relationship was statistically significant in two colonies and the combined results were significant. The results of the first study suggest the generally weak relationships found in this second study.     

Informational conflicts created by the waggle dance

The honeybee (Apis mellifera) waggle dance is one of the most intriguing animal communication signals. A dancing bee communicates the location of a profitable food source and its odour. Followers may often experience situations in which dancers indicate an unfamiliar location but carry the scent of a flower species the followers experienced previously at different locations. Food scents often reactivate bees to resume food collection at previously visited food patches. This double function of the dance creates a conflict between the social vector information and the private navigational information. We investigated which kind of information followers with field experience use in this situation and found that followers usually ignored the spatial information encoded by the waggle dance even if they followed a dance thoroughly (five waggle runs or more). They relied on private information about food source locations instead (in 93% of all cases). Furthermore, foragers preferred to follow dancers carrying food odours they knew from previous field trips, independently of the spatial information encoded in the dance. Surprisingly, neither odour identity nor the location indicated by the dancer was an important factor for the reactivation success of a dance. Our results contrast with the assumption that (i) followers usually try to decode the vector information and (ii) dances indicating an unfamiliar location are of little interest to experienced foragers.     

Waggle dance behavior associated with seasonal absconding in colonies of the African honey bee,Apis mellifera scutellata

Summary Waggle dance activity associated with seasonal absconding (migration) was investigated in two colonies of the African honey bee. Prior to absconding, waggle dances regularly communicated distances up to 10–20 km from the nests. However, compared to waggle dances observed during nonabsconding periods, those occurring prior to migration were less associated with food sources, occurred during periods of little or no flight activity, and exhibited great variability in the communication of distance by consecutive waggle runs of individual bees. It is therefore unlikely that migration dances communicated the locations of, or stimulated immediate recruitment for, specific foraging or nesting sites. Rather, the dances may have functioned to establish a general route of travel. The majority of migration dances observed were oriented in an easterly direction, and upon departure both colonies traveled towards the E-SE. The orientation of migration dances occurred independently of the directions communicated by waggle dances associated with past foraging success or the sampling of alternate foraging areas. Migration dance orientation may have been affected by prevailing wind directions, because during the migration period winds blew primarily from the east. However, it is unlikely that wind direction was the only factor influencing migration dance orientation. The lack of immediate flight activity associated with migration dance performance suggests the dances may have gradually prepared colonies for migratory movement by conveying a message to fly for a long, but unspecified distance in a certain direction. Waggle dances associated with migration may therefore function differently from those associated with foraging and nest site selection, which convey both the distance and direction to specific locations.     

Spatial foraging patterns and colony energy status in the African honey bee,Apis mellifera scutellata

The relationship between changes in foraging patterns (inferred from waggle dance activity) and colony energy status (inferred from brood rearing activity, food storage, and colony weight) was examined for the African honey bee during a period of relative resource abundance and resource dearth. When resources were more abundant mean foraging distances (about 400 m) and foraging areas (4–5 km²) were small, and colonies recruited to 12–19 different sites per day. Colony foraging ranges and sites visited increased slightly during the dearth period, yet foraging continued to be concentrated within less than 10 km². The degree to which fluctuations in foraging patterns were correlated with colony energy status varied with the availability of floral resources. During periods of relative forage abundance, increases in foraging range and number of sites visited were significantly correlated with increases in brood rearing and colony weight. In contrast, colonies examined during periods of resource dearth exhibited no correlations between foraging areas, foraging distances, and fluctuations in brood rearing, food storage, or colony weight. Thus, during dearth periods colonies may not be able to coordinate foraging patterns with changes in colony energy status.     

Benefits of recruitment in honey bees: effects of ecology and colony size in an individual-based model

Why do some social insects have sophisticated recruitment systems,while other species do not communicate about food source locationsat all? To answer this question, it is necessary to identifythe social or ecological factors that make recruitment adaptiveand thus likely to evolve. We developed an individual-basedmodel of honey bee foraging to quantify the benefits of recruitmentunder different spatial distributions of nondepleting resourcepatches and with different colony sizes. Benefits of recruitmentwere strongly dependent on resource patch quality, density,and variability. Communication was especially beneficial ifpatches were poor, few, and variable. A sensitivity analysisof the model showed that under conditions of high resource densityrecruitment could even become detrimental, especially if foragingduration was short, tendency to scout was high, or recruitsneeded a long time to find communicated locations. Colony size,a factor often suspected to influence recruitment evolution,had no significant effect. These results may explain the recentexperimental findings that in honey bees, benefits of waggledance recruitment seem to vary seasonally and with habitat.They may also explain why some, but not other, species of socialbees have evolved a strategy to communicate food locations tonest mates.     

Factors influencing seasonal absconding in colonies of the African honey bee,Apis mellifera scutellata

Summary This study investigated the effects of colony growth and development, food storage, foraging activity and weather on the migration behavior of African honey bees in the Okavango River Delta, Botswana. Four observation colonies were studied during the honey bee migration season (November–May), at which time the availability of blooming species was reduced. Two of the colonies (colonies 1 & 2) migrated during the study period, while the remaining two (colonies 3 & 4) did not. During the 4–6 weeks preceding the onset of migration preparations, colonies 1 & 2 exhibited increasing population sizes, high levels of brood production with low brood mortality, relatively large stores of food, and increasing mass. In contrast, the populations of colonies 3 & 4 did not increase, brood-rearing activity was erratic and lower, brood mortality was higher, food stores became depleted and colony mass declined. Both colonies 3 & 4 ceased rearing brood, and colony 3 died of starvation. Colony foraging activity was examined by monitoring waggle-dance activity 2–3 days each week. For 4–6 weeks before the onset of migration in colonies 1 & 2, daily foraging areas and mean daily foraging distances became increasingly large and variable. Colonies 3 & 4 exhibited foraging patterns similar to those observed for colonies 1 & 2 preceding migration. There was no clear association between 7 weather parameters examined and migration behavior. These data suggest that migration is influenced by an interaction of intra-colony demographics, food reserves and foraging patterns. Migration may be feasible only for those colonies that possess (1) a population of appropriate size and age structure to compensate for the natural attrition of older workers during the emigration process, and (2) sufficient food reserves for long-distance travel and the establishment of a new nest. Changing foraging patterns may reflect a deteriorating foraging environment, which may trigger the onset of migration preparations, provided that colony demographics and food reserves are conducive. Colonies that show decreased brood production, higher brood mortality and reduced food stores may be incapable of migrating, even when experiencing deteriorating foraging conditions. Rather, such colonies may have a greater chance of survival if they attempt to persist in a given area.     

The vibration dance behavior of queenless workers of the honey bee,Apis mellifera (Hymenoptera: Apidae)

The vibration dance was investigated in queenless (QL) colonies of honey bees. Workers performing the dance had significantly less-developed ovaries than recipients. Vibrators were more likely to be mauled by nestmates (an aggressive act) and were more strongly associated with foraging than were nonvibrating controls. Recipients responded to the dance by increasing the amount of time spent performing tasks. The vibration dance may therefore be associated with aggression in QL colonies and may give workers with less-developed ovaries a degree of control over the behavior of bees with greater ovarian development.     

The effects of season,pretraining, and scent on the efficiency of traps for capturing recruited honey bees (Hymenoptera: Apidae)

A portable trap was designed to capture honey bees recruited to the field by dancers. An infrared phototransistor placed in the entrance tunnel of the trap sensed an incoming bee and turned on a talking clock, which in turn activated a voice-actuated audio tape recorder that recorded the time. We tested the effectiveness of traps for capturing bees recruited by four dancer bees (1) during two seasons when local flower densities differed, (2) with or without a group of bees pretrained to enter traps for food, and (3) when the scent used in traps and at the dancers' feeding station was changed just prior to recruitment trials or was not changed. One trap was put out at each of four distances (50, 100, 150, and 200 m) from the hive, while dancers fed on concentrated sucrose at the feeding station located at 150 m in the same direction. Recruited bees that approached the traps but did not enter were counted by observers. More bees were recruited and captured in traps when the local flora was sparse (fall) than when flowers were abundant (summer), when bees were pretrained versus not pretrained, and when the scent was not changed just prior to recruitment trials versus changed. The distributions of number of bees counted at the four distances at scented recruit stations and trapped were similar only when bees were pretrained and the scent was not changed during recruitment trials. However, the highest proportion of bees trapped in a trial at 150 m (distance to dancers' feeding station) was when bees were pretrained and the scent was changed.     

An exploration of the relationship between recruitment communication and foraging in stingless bees

Social information is widely used in the animal kingdom and can be highly adaptive. In social insects, foragers can use social information to find food, avoid danger, or choose a new nest site. Copying others allows individuals to obtain information without having to sample the environment. When foragers communicate information they will often only advertise high-quality food sources, thereby filtering out less adaptive information. Stingless bees, a large pantropical group of highly eusocial bees, face intense inter- and intra-specific competition for limited resources, yet display disparate foraging strategies. Within the same environment there are species that communicate the location of food resources to nest-mates and species that do not. Our current understanding of why some species communicate foraging sites while others do not is limited. Studying freely foraging colonies of several co-existing stingless bee species in Brazil, we investigated if recruitment to specific food locations is linked to 1) the sugar content of forage, 2) the duration of foraging trips, and 3) the variation in activity of a colony from 1 day to another and the variation in activity in a species over a day. We found that, contrary to our expectations, species with recruitment communication did not return with higher quality forage than species that do not recruit nestmates. Furthermore, foragers from recruiting species did not have shorter foraging trip durations than those from weakly recruiting species. Given the intense inter- and intraspecific competition for resources in these environments, it may be that recruiting species favor food resources that can be monopolized by the colony rather than food sources that offer high-quality rewards.     

The distribution of Paenibacillus larvae spores in adult bees and honey and larval mortality, following the addition of American foulbrood diseased brood or spore-contaminated honey in honey bee (Apis mellifera) colonies

Within colony transmission of Paenibacillus larvae spores was studied by giving spore-contaminated honey comb or comb containing 100 larvae killed by American foulbrood to five experimental colonies respectively. We registered the impact of the two treatments on P. larvae spore loads in adult bees and honey and on larval mortality by culturing for spores in samples of adult bees and honey, respectively, and by measuring larval survival. The results demonstrate a direct effect of treatment on spore levels in adult bees and honey as well as on larval mortality. Colonies treated with dead larvae showed immediate high spore levels in adult bee samples, while the colonies treated with contaminated honey showed a comparable spore load but the effect was delayed until the bees started to utilize the honey at the end of the flight season. During the winter there was a build up of spores in the adult bees, which may increase the risk for infection in spring. The results confirm that contaminated honey can act as an environmental reservoir of P. larvae spores and suggest that less spores may be needed in honey, compared to in diseased brood, to produce clinically diseased colonies. The spore load in adult bee samples was significantly related to larval mortality but the spore load of honey samples was not.