Tandem Recruitment and Foraging in the Ponerine Ant <Emphasis Type="Italic">Pachycondyla harpax</Emphasis> (Fabricius)

Tandem running is a common recruitment strategy in ant species with small colony sizes. During a tandem run, an informed leader guides a usually naïve nestmate to a food source or a nest site. Some species perform tandem runs only during house hunting, suggesting that tandem running does not always improve foraging success in species known to use tandem running as a recruitment strategy, but more natural history information on tandem running under natural conditions is needed to better understand the adaptive significance of tandem recruitment in foraging. Studying wild colonies in Brazil, we for the first time describe tandem running in the ponerine ant Pachycondyla harpax (Fabricius). We asked if foragers perform tandem runs to carbohydrate- (honey) and protein-rich (cheese) food items. Furthermore, we tested whether the speed and success rate of tandem runs depend on the foraging distance. Foragers performed tandem runs to both carbohydrate food sources and protein-rich food items that exceed a certain size. The probability to perform a tandem run and the travelling speed increase with increasing foraging distances, which could help colonies monopolize more distant food sources in a competitive environment. Guiding a recruit to a food source is costly for leaders as ants are ~66% faster when travelling alone. If tandem runs break up (~23% of all tandem runs), followers do not usually discover the food source on their own but return to the nest. Our results show that tandem running to food sources is common in P. harpax, but that foragers modify their behaviour according to the type of food and its distance from the nest. Competition with other ants was intense and we discuss how tandem running in P. harpax might help colonies to build-up a critical number of ants at large food items that can then defend the food source against competitors.     

Sticking to their choice – honey bee subfamilies abandon declining food sources at a slow but uniform rate

Abstract. 1. The allocation of honey bee foragers among food patches is a result of decisions made by individual bees that are based on internal and external cues.
2. Decision-making processes are often based on internal thresholds. For example, if the quality of the food source is assessed by a forager as exceeding its internal threshold, the bee will continue foraging on that food source.
3. It is often assumed that all individuals have the same threshold and therefore use the same thresholds in decision-making, but because the honey bee queen mates with 12–30 males, the workers within a colony are genetically heterogeneous. Thus, the thresholds used by individual bees may be genetically variable within a colony.
4. Models of colony-level foraging behaviour of honey bees suggest that the rate of abandoning food sources is a critical parameter affecting foraging success. Moreover, these models show that variance among subfamilies in their abandonment rates may increase the colony's foraging efficiency.
5. Experimental data showing the relationship between the probability of abandoning a food source and its profitability are lacking, as is information on any variation in abandonment rates among subfamilies.
6. Abandonment rates were determined experimentally for four honey bee families for seven different sucrose concentrations. The results showed that abandonment rates appear to be invariant among (sub)families. The importance of forager fidelity to declining food sources is discussed with respect to foraging efficiency in a changing environment.     

Foraging arena size and structural complexity affect the dynamics of food distribution in ant colonies

Food acquisition by ant colonies is a complex process that starts with acquiring food at the source (i.e., foraging) and culminates with food exchange in or around the nest (i.e., feeding). While ant foraging behavior is relatively well understood, the process of food distribution has received little attention, largely because of the lack of methodology that allows for accurate monitoring of food flow. In this study, we used the odorous house ant, Tapinoma sessile (Say) to investigate the effect of foraging arena size and structural complexity on the rate and the extent of spread of liquid carbohydrate food (sucrose solution) throughout a colony. To track the movement of food, we used protein marking and double-antibody sandwich enzyme-linked immunosorbent assay, DAS-ELISA. Variation in arena size, in conjunction with different colony sizes, allowed us to test the effect of different worker densities on food distribution. Results demonstrate that both arena size and colony size have a significant effect on the spread of the food and the number of workers receiving food decreased as arena size and colony size increased. When colony size was kept constant and arena size increased, the percentage of workers testing positive for the marker decreased, most likely because of fewer trophallactic interactions resulting from lower worker density. When arena size was kept constant and colony size increased, the percentage of workers testing positive decreased. Nonrandom (clustered) worker dispersion and a limited supply of food may have contributed to this result. Overall, results suggest that food distribution is more complete is smaller colonies regardless of the size of the foraging arena and that colony size, rather than worker density, is the primary factor affecting food distribution. The structural complexity of foraging arenas ranged from simple, two-dimensional space (empty arenas) to complex, three-dimensional space (arenas filled with mulch). The structural complexity of foraging arenas had a significant effect on food distribution and the presence of substrate significantly inhibited the spread of food. Structural complexity of foraging arenas and the resulting worker activity patterns might exert considerable influence on socioecological processes in ants and should be considered in laboratory assays.     

Social organization of colony movement in the tropical ponerine ant,Diacamma rugosum (Le Guillou)

This work is part of a study on the social organization ofDiacamma rugosum, a large ponerine ant, which lacks a distinctive reproductive queen. This ant forms a small colony and frequently changes its nest site when the environmental conditions become unfavourable. Experiments in the laboratory showed that slight physical disturbances easily caused colony movement. The process of movement consisted of 3 successive phases: a) an exploration period, b) an movement period and c) a final movement period. The movement was organized by leader ants and 5 to 25% of all workers became leaders. These workers showed both tandem running and carrying behaviour during movement, tandem running being employed to recruit workers, whereas carrying behaviour was strictly limited to carrying eggs, larvae, pupae and males. During movement most of the tandem leader ants are those engaged in outdoor works in daily life. Potential of workers to become tandem leaders was correlated with outside works undertaken in daily life.     

To be or not to be faithful: flexible fidelity to foraging trails in the leaf‐cutting ant Acromyrmex lobicornis

1. Ants using trails to forage have to select between two alternative routes at bifurcations, using two, potentially conflicting, sources of information to make their decision: individual experience to return to a previous successful foraging site (i.e. fidelity) and ant traffic. In the field, we investigated which of these two types of information individuals of the leaf‐cutting ant Acromyrmex lobicornis Emery use to decide which foraging route to take. 2. We measured the proportion of foraging ants returning to each trail of bifurcations the following day, and for 4–7 consecutive days. We then experimentally increased ant traffic on one trail of the bifurcation by adding additional food sources to examine the effect of increased ant traffic on the decision that ants make. 3. Binomial tests showed that for 62% of the trails, ant fidelity was relatively more important than ant traffic in deciding which bifurcation to follow, suggesting the importance of previous experience. 4. When information conflict was generated by experimentally increasing ant traffic along the trail with less foraging activity, most ants relied on ant traffic to decide. However, in 33% of these bifurcations, ants were still faithful to their trail. Thus, there is some degree of flexibility in the decisions that A. lobicornis make to access food resources. 5. This flexible fidelity results in individual variation in the response of workers to different levels of ant traffic, and allows the colony to simultaneously exploit both established and recently discovered food patches, aiding efficient food gathering.     

On foraging,recruitment systems and optimum number of scouts in eusocial colonies

Summary A numerical model of an eusocial colony foraging for food showed that, for each set of values of resource density, resource size and recruitment system employed, a given optimal proportion of scouts in the colony maximize the amount of resources retrieved by a colony during a fixed period. The model predicts that ants using mass recruitment systems should have larger colonies with small foragers, and should forage on large food sources. Retrieval of small food sources by small colonies is best achieved with large workers using individual foraging strategies. For mass foragers, several food sources are best retrieved using democratic decision-making systems in recruitment, whereas for very large food sources at very low mean food patch density, autocratic decision-making systems are optimal. Some of the experimental evidence available is discussed in the light of these findings, as they confirm the prediction that large colonies with small workers have mass recruitment systems, whereas workers of small colonies with large workers are generally lone foragers.     

Recruitment-dance signals draw larger audiences when honey bee colonies have multiple patrilines

Honey bee queens (Apis mellifera) who mate with multiple males produce colonies that are filled with numerous genetically distinct patrilines of workers. A genetically diverse colony benefits from an enhanced foraging effort, fuelled in part by an increase in the number of recruitment signals that are produced by foragers. However, the influence of patriline diversity on the attention paid to these signals by audiences of potentially receptive workers remains unexplored. To determine whether recruitment dances performed by foragers in multiple-patriline colonies attract a greater number of dance followers than dances in colonies that lack patriline diversity, we trained workers from multiple- and single-patriline colonies to forage in a greenhouse and monitored their dance-following activity back in the hives. On average, more workers followed a dance if it was performed in a multiple-patriline colony rather than a single-patriline colony (33% increase), and for a greater number of dance circuits per follower. Furthermore, dance-following workers in multiple-patriline colonies were more likely to exit their hive after following a dance, although this did not translate to a difference in colony-level exit rates between treatment types. Recruiting nest mates to profitable food sources through dance communication is critical to a colony’s foraging success and long-term fitness; polyandrous queens produce colonies that benefit not only from increased recruitment signalling, but also from the generation of larger and more attentive audiences of signal receivers. This study highlights the importance of integrating responses of both signal senders and receivers to understand more fully the success of animal-communication systems.     

Foraging behavior of the queenless ant Dinoponera quadriceps Santschi (Hymenoptera: Formicidae)

The search for and ingestion of food are essential to all animals, which spend most of their lives looking for nutritional sources, more than other activities such as mating, intra-specific disputes or escaping from predators. The present study aims to describe and quantify several aspects of foraging behavior, diet and food transport in the queenless ant Dinoponera quadriceps Santschi in a secondary Atlantic forest, Northeastern Brazil. Three colonies were randomly selected at a distance of at least 50 m from one another. On leaving the colony, worker ants were followed until their return, with no nutritional provision or interference with their activities. Activities were recorded using focal time sampling with instantaneous recording every minute for 10 consecutive minutes. Each colony was observed 1 day/week, for at least 6 h/day resulting in 53.8h of direct observation of the workers. Foraging activities, success in transporting food, type of food, cleaning and interaction among the workers were recorded. Foraging was always individual, with no occurrence of recruitment. Diet was composed mainly of arthropods, mostly insects. The collection of small fruits (Eugenia sp.) was also observed. Foraging time was greater when workers transported food to the colony, the return time being shorter than the foraging period, suggesting the use of chemical and visual cues for orientation during their foraging and food-collecting activities.     

Distributed leadership and adaptive decision-making in the ant Tetramorium caespitum

In the ant species Tetramorium caespitum, communication and foraging patterns rely on group-mass recruitment. Scouts having discovered food recruit nestmates and behave as leaders by guiding groups of recruits to the food location. After a while, a mass recruitment takes place in which foragers follow a chemical trail. Since group recruitment is crucial to the whole foraging process, we investigated whether food characteristics induce a tuning of recruiting stimuli by leaders that act upon the dynamics and size of recruited groups. High sucrose concentration triggers the exit of a higher number of groups that contain twice as many ants and reach the food source twice as fast than towards a weakly concentrated one. Similar trends were found depending on food accessibility: for a cut mealworm, accessibility to haemolymph results in a faster formation of larger groups than for an entire mealworm. These data provide the background for developing a stochastic model accounting for exploitation patterns by group-mass recruiting species. This model demonstrates how the modulations performed by leaders drive the colony to select the most profitable food source among several ones. Our results highlight how a minority of individuals can influence collective decisions in societies based on a distributed leadership.     

Colony foraging allocation is finely tuned to food distance and sweetness even close to a bee colony

Social bee colonies can allocate their foraging resources over a large spatial scale, but how they allocate foraging on a small scale near the colony is unclear and can have implications for understanding colony decision‐making and the pollination services provided. Using a mass‐foraging stingless bee, Scaptotrigona pectoralis (Dalla Torre) (Hymenoptera: Apidae: Meliponini), we show that colonies will forage near their nests and allocate their foraging labor on a very fine spatial scale at an array of food sources placed close to the colony. We counted the foragers that a colony allocated to each of nine feeders containing 1.0, 1.5, or 2.0 M sucrose solution [31, 43, and 55% sucrose (wt/wt), respectively] at distances of 10, 15, and 20 m from the nest. A significantly greater number of foragers (2.6–5.3 fold greater) visited feeders placed 10 vs. 20 m away from the colony. Foraging allocation also corresponded to food quality. At the 10‐m feeders, 4.9‐fold more foragers visited 2.0 M as compared to 1.0 M sucrose feeders. Colony forager allocation thus responded to both differences in food distance and quality even when the travel cost was negligible compared to normal colony foraging distances (10 m vs. an estimated 800–1 710 m). For a nearby floral patch, this could result in unequal floral visitation and pollination.     

Foraging decisions of individual workers vary with colony size in the greenhead ant Rhytidoponera metallica (Formicidae, Ectatomminae)

Summary. The ability of worker ants to adapt their behaviour depending on the social environment of the colony is imperative for colony growth and survival. In this study we use the greenhead ant Rhytidoponera metallica to test for a relationship between colony size and foraging behaviour. We controlled for possible confounding ontogenetic and age effects by splitting large colonies into small and large colony fragments. Large and small colonies differed in worker number but not worker relatedness or worker/brood ratios. Differences in foraging activity were tested in the context of single foraging cycles with and without the opportunity to retrieve food. We found that workers from large colonies foraged for longer distances and spent more time outside the nest than foragers from small colonies. However, foragers from large and small colonies retrieved the first prey item they contacted, irrespective of prey size. Our results show that in R. metallica, foraging decisions made outside the nest by individual workers are related to the size of their colony.Received 23 March 2004; revised 3 June 2004; accepted 4 June 2004.     

Bumble bees (Bombus terrestris) store both food and information in honeypots

Social insect foragers often transmit information about foodsources to nest mates. In bumble bees (Bombus terrestris), forexample, successful foragers use excited motor displays anda pheromone as communication signals. In addition, bees couldmake use of an indirect pathway of information flow, via thehoney stores. We show here that, indeed, bees in the nest continuouslymonitor honeypots and sample their contents, thus obtaininginformation on supply and demand of nectar. When there is aninflux of nectar into the nest, the colony deploys more workersfor foraging. The number of new foragers depends on sugar concentration.Foragers returning with high-quality sugar solution displaymore "excited runs" on the nest structure. The recruits' response,however, does not depend on modulated behavior by foragers:more workers start to forage with high quality of incoming nectar,even when this nectar is brought by a pipette. Moreover, weshow that the readiness of bees to respond to recruitment signalsor incoming nectar also depends on colony demand. When colonynectar stores are full, the response of bees to equal amountsof nectar influx is smaller than when stores are empty. Whencolony nectar stores are depleted, foragers spend more timerunning excitedly and less time probing pots in the nest andrun with higher average speed, possibly to disperse the alertingpheromone more efficiently. However, more bees respond to nectarinflux to empty stores, whether or not this is accompanied byforager signals. Thus, honeypots serve to store informationas well as food.     

Honey bee dance communication: waggle run direction coded in antennal contacts?

The behaviour of 38 honeybee dance followers and the patterns of antennal contact between followers and dancer were monitored during ten waggle runs for a feeding site 1200 m from the hive. The analysis was restricted to waggle runs with a maximum of 5 followers, allowing the followers to choose between different positions around the dancer. At the beginning of the waggle run, followers are rather evenly spaced around the dancer. During the waggle run, the followers tend to accumulate at the rear end of the dancer. At the end of the waggle run, all followers are found in a ±60° arc behind the dancer. The body orientation angles of the followers depend on their position relative to the dancer. The follower bees have intense antennal contact with the dancer. At least one temporal parameter of the contact pattern may inform the followers about their position relative to the dancer, may guide the dance followers to the rear end of the dancer and may allow them to extract information about the location of the food source advertised by the dance. The role of antennal contact for dance communication appears to have been underestimated in previous studies. Accepted: 20 February 1999     

Genetic diversity within honeybee colonies increases signal production by waggle-dancing foragers

Recent work has demonstrated considerable benefits of intracolonial genetic diversity for the productivity of honeybee colonies: single-patriline colonies have depressed foraging rates, smaller food stores and slower weight gain relative to multiple-patriline colonies. We explored whether differences in the use of foraging-related communication behaviour (waggle dances and shaking signals) underlie differences in foraging effort of genetically diverse and genetically uniform colonies. We created three pairs of colonies; each pair had one colony headed by a multiply mated queen (inseminated by 15 drones) and one colony headed by a singly mated queen. For each pair, we monitored the production of foraging-related signals over the course of 3 days. Foragers in genetically diverse colonies had substantially more information available to them about food resources than foragers in uniform colonies. On average, in genetically diverse colonies compared with genetically uniform colonies, 36% more waggle dances were identified daily, dancers performed 62% more waggle runs per dance, foragers reported food discoveries that were farther from the nest and 91% more shaking signals were exchanged among workers each morning prior to foraging. Extreme polyandry by honeybee queens enhances the production of worker-worker communication signals that facilitate the swift discovery and exploitation of food resources.     

Foraging in honeybees--when does it pay to dance?

Honeybees are unique in that they are the only social insectsthat are known to recruit nest mates using the waggle dance.This waggle dance is used by successful foragers to convey informationabout both the direction and distance to food sources. Nestmates can use this spatial information, increasing their chancesof locating the food source. But how effective is the bees'dance communication? Previous work has shown that dancing doesnot benefit a honeybee colony under all foraging conditionsand that the benefits of dancing are small. We used an individual-basedsimulation model to investigate under which foraging conditionsit pays to dance. We compared the net nectar intake of 3 typesof colonies: 1) colonies that use dance communication; 2) coloniesthat did dance but could not use the dance's spatial information;and 3) colonies that did not dance. Our results show that dancingis beneficial when the probability of independent discoveryof food sources is low. Low independent discovery rates occurwhen patches are very small or very far away. Under these conditions,dancing is beneficial as only a single individual needs to finda patch for the whole colony to benefit. The main benefit ofthe honeybee's dance communication, however, seems to be thatit enables the colony to forage at the most profitable patchesonly, ignoring forage patches that are of low quality. Thus,dancing allows the colony to rapidly exploit high-quality patches,thereby preventing both intra- and interspecific competitorsfrom using that same patch.     

The influence of forager number and colony size on food distribution in the odorous house ant, Tapinoma sessile

Stomodeal trophallaxis plays a major role in ant colony nutrition and communication. While the rate of food distribution at the individual level (worker to worker) is rapid, factors affecting the rate of food distribution at the colony level remain poorly understood. We used the odorous house ant, Tapinoma sessile (Say), as a model species to investigate the factors affecting the rate of spread of liquid carbohydrate food throughout a colony. To track the movement of the food we used protein marking and double antibody sandwich enzyme-linked immunosorbent assay, DAS-ELISA. Increasing colony size while keeping the number of donor workers constant significantly decreased the number of individuals testing positive for the marker. After 8 h of trophallactic interactions with ten donors, 92 ± 5% of recipient workers tested positive in a colony of 125 and 38 ± 5% tested positive in a colony of 1,000. Interestingly, as colony size increased and the percentage of workers testing positive decreased, the proportion of workers actually receiving food increased. Food originating from a single donor fed approximately 12 individuals in colonies comprised of 125 recipients and approximately 38 individuals in colonies comprised of 1,000 recipients. Thus, the per capita consumption of food decreased as colony size increased, most likely because the amount of food reaching the colony was limited. Increasing the number of donors while keeping colony size constant significantly increased the number of recipient ants testing positive for the marker. As the number of donor workers doubled, the percentage of recipients testing positive more than doubled suggesting that the number of individuals receiving food increases with increasing colony size, while the per capita amount of food decreases. When food was available ad libitum and in close proximity to the nest, numerous workers fed directly at the food source. This dramatically increased the rate and the extent of food distribution to both the workers and the queens and colony size had no significant effect on the spread of the marker in the workers or the queens. The rate and the extent of food distribution at the colony level may depend on a number of factors including the number of successful foragers, the size and density of the recipient colony, and the recipient caste.     

Red-gartered Coot Fulica armillata feeding on the grapsid crab Cyrtograpsus angulatus: advantages and disadvantages of an unusual food resource

The behaviour of Red-gartered Coots feeding on an unusual food source was examined at Mar Chiquita Coastal Lagoon, Argentina. The grapsid crab Cyrtograpsus angulatus made up all observed prey items, and 61% were small. Both handling and foraging duration increased with the size of captured crabs, but foraging efficiency decreased. Crab availability affected both the dive duration of the Coots and their foraging decisions with regard to prey-size selection. Two species of gull were observed kleptoparasitizing Coots, especially when the Coot was handling medium or large crabs. Feeding by Coots on Cyrtograpsus angulatus has not been previously documented and may be a feeding innovation. Our estimations suggest that Coots were foraging optimally, since smaller crabs were more energetically profitable.     

Adjustments in the Time,Distance and Direction of Foraging in Dinoponera quadriceps Workers

We measured individual decisions regarding the adjustments of time, distance and direction of foraging in Dinoponera quadriceps. We observed two colonies in an area of secondary Atlantic Forest, FLONA-ICMBio, in Northeastern Brazil. The workers were individually marked. We recorded the displacement of workers, their returns to the nest with and without food, the time spent searching for food, maximum and total distance, inter-trip latency and direction of trips. The time spent searching for food, maximum distance and transport velocity did not vary with food size. The previous trip success reduced the latency between foraging trips and increased the percentage of success on the next trip. However, this previous success did not demonstrate a significant variation relative to the time spent searching on the next trip or direction of search. The workers maintained an individual directional fidelity during foraging. The adjustments of these foraging variables under individual control contributed to the efficiency at the colony level. D. quadriceps is compatible with the central place theory and risk sensitivity model of behavior.     

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.     

Negative Feedback Enables Fast and Flexible Collective Decision-Making in Ants

Positive feedback plays a major role in the emergence of many collective animal behaviours. In many ants pheromone trails recruit and direct nestmate foragers to food sources. The strong positive feedback caused by trail pheromones allows fast collective responses but can compromise flexibility. Previous laboratory experiments have shown that when the environment changes, colonies are often unable to reallocate their foragers to a more rewarding food source. Here we show both experimentally, using colonies of Lasius niger, and with an agent-based simulation model, that negative feedback caused by crowding at feeding sites allows ant colonies to maintain foraging flexibility even with strong recruitment to food sources. In a constant environment, negative feedback prevents the frequently found bias towards one feeder (symmetry breaking) and leads to equal distribution of foragers. In a changing environment, negative feedback allows a colony to quickly reallocate the majority of its foragers to a superior food patch that becomes available when foraging at an inferior patch is already well underway. The model confirms these experimental findings and shows that the ability of colonies to switch to a superior food source does not require the decay of trail pheromones. Our results help to resolve inconsistencies between collective foraging patterns seen in laboratory studies and observations in the wild, and show that the simultaneous action of negative and positive feedback is important for efficient foraging in mass-recruiting insect colonies.