The role of motivation in the performance of a conditioned switching-over of the maze habit in ants Myrmica rubra after a change in the quality of the food reinforcement

Active foragers Myrmica rubra were trained in a maze under conditions of different levels of colony need in food with carbohydrate (sugar syrup) or protein (ants Lasius niger pupae) reinforcement. Acquisition of the maze habit was better under conditions of reinforcement with pupae, especially by its time indices. Ants were able to modify the acquired habit when the reinforcement quality was changed. It was shown that learning was possible only when the colony and after a change pupae for the syrup was "hungry". Under these conditions, after a change of the syrup for pupae or visa versa the previously acquired optimum habit was transferred. Several hours later, with satiation of the colony, food reactions learned with protein reinforcement switched-over to "stochastic" non-optimized behavior with the dominance of exploratory reactions. Thus, it was shown that higher social insects ants were capable for conditioned switching-over. Different forms of this phenomenon depended on the level of the colony need in food and, consequently, on the level of the social food motivation of foragers ants.     

The capacity of ants for multiple alterations in the maze habit]

Ability was shown of ants Myrmica rubra to multiple reconstructions of the habit elaborated in symmetrical multialternative maze under motivation of care for the progeny (transportation of breed of the own species). Reconstruction consisted in the change of reinforcement location on the left or right aim spot. The ants showed the ability to carry out the series of eight reconstructions during one-two days. An improvement took place of the fulfillment of the last reconstructions in comparison with the first ones. Peculiarities of learning and reconstructions were found in two groups of animals differing by conditions of learning: at reinforcement on both ain spors or on one of them. The results obtained are considered as indices of high plasticity of the behaviour of ants of the studied species.     

The cost of being queen: Investment across Pogonomyrmex harvester ant gynes that differ in degree of claustrality

The role of the ant colony largely consists of non-reproductive tasks, such as foraging, tending brood, and defense. However, workers are vitally linked to reproduction through their provisioning of sexual offspring, which are produced annually to mate and initiate new colonies. Gynes (future queens) have size-associated variation in colony founding strategy (claustrality), with each strategy requiring different energetic investments from their natal colony. We compared the per capita production cost required for semi-claustral, facultative, and claustral gynes across four species of Pogonomyrmex harvester ants. We found that the claustral founding strategy is markedly expensive, costing approximately 70% more energy than that of the semi-claustral strategy. Relative to males, claustral gynes also had the largest differential investment and smallest size variation. We applied these investment costs to a model by Brown and Bonhoeffer (2003) that predicts founding strategy based on investment cost and foraging survivorship. The model predicts that non-claustral foundresses must survive the foraging period with a probability of 30–36% in order for a foraging strategy to be selectively favored. These results highlight the importance of incorporating resource investment at the colony level when investigating the evolution of colony founding strategies in ants.     

Semi-claustral colony founding in the seed-harvester ant Pogonomyrmex californicus: a comparative analysis of colony founding strategies

The evolution of queens that rear their first brood solely using body reserves, i.e. fully claustral, is viewed as a major advance for higher ants because it eliminated the need for queens to leave the nest to forage. In an apparently unusual secondary modification, the seed-harvester ant Pogonomyrmex californicus displays obligate queen foraging, i.e. queens must forage to garner the resources necessary to survive and successfully rear their first brood. I examined the potential benefits of queen foraging by comparing ecological and physiological traits between P. californicus and several congeners in which the queen can rear brood using only body reserves. The primary advantage of foraging appears to lie in providing the queens of P. californicus with the energy to raise significantly more brood than possible by congeners that use only body reserves; the workers reared in the first brood were also heavier in mass than that predicted by their head width. Other correlates of queen foraging in P. californicus relative to tested congeners included a significantly lower total fat content for alate queens, a small queen body size, and a low queen to worker body mass ratio. Queens also forage in several other well-studied species of Pogonomyrmex, suggesting the possibility that queen foraging may be more common than previously thought in higher ants.     

A technological approach to the description of group foraging in the ant <Emphasis Type="Italic">Myrmica rubra</Emphasis>

Group foraging in Myrmica rubra ants is considered as a cyclic process in which transition from one phase to another is determined by summation of actions of individual ants inside the nest and in the foraging territory. In its turn, individual behavior is considered as a labile sequence of tasks, such as territory exploration, acquiring and transportation of food, the completeness of the sequence depending on the individual experience. Data on foraging of three experimental M. rubra colonies were represented as a relational database in MS Access 2007, and the database tools were used to study the interrelated characteristics of the two levels of the foraging process (group and individual) and to analyze the quantitative parameters of individual and group behavior.     

The Behavior of <Emphasis Type="Italic">Acromyrmex crassispinus</Emphasis> (Hymenoptera: Formicidae) on Trail Bifurcations and the Influence of Ant Flow on Error Rates of Nestbound Laden Workers

Ants are ordinarily faced with a succession of bifurcations along their foraging networks. Given that there is no directionality in pheromone trails, each bifurcation is potentially an opportunity for error in the trajectory of laden workers to the nest, which could entail considerable inefficiencies in the transportation of food to the colony. Leaf-cutting ants (Atta and Acromyrmex) commonly show intense traffic and complex foraging trail systems, which make them ideal organisms to study worker behavior in trail bifurcations. The behavior of leaf-cutting ants of the genus Acromyrmex in trail bifurcations is still largely unexplored. Thus, this study aimed to assess the behavior of Acromyrmex crassispinus workers on trail bifurcations and to investigate whether differences in ant flow on foraging trails influence the error rate of nestbound laden workers at trail bifurcation. There was a negative relationship between ant flow and error rate of nestbound laden workers. Most workers walked in the central part of the foraging trails but occupied a broader area of the foraging trail when the ant flow was high. The results of this study provide valuable insight into the organization of traffic flow in A. crassispinus and its impacts on the foraging strategy of the species.     

Division of labor inPonera pennsylvannica (Formicidae: Ponerinae)

Summary We examined division of labor and colony demography in the antPonera pennsylvannica. Observation of three colonies with individually marked workers revealed a high degree of interindividual behavioral variation and a rough but consistent division of labor between brood tenders and foragers. This division was present both in colonies consisting entirely of workers produced in the previous summer and in colonies containing freshly eclosed ants. Two colonies showed typical age-based polyethism, with young ants focusing on brood care and overwintered ants on foraging. No such age basis was detected in the third colony. This difference may relate to variability in brood production schedules. Colonies showing temporal polyethism had two peaks of brood production and thus had relatively large brood populations when the first young workers eclosed, while the third colony had only one peak and little brood for the young workers to tend. Even if young ants have a lower threshold for brood care, it may have been concealed in the latter situation. Demographic data indicate that natural colonies produce one brood per year and that workers typically eclose into colonies with relatively low brood care demands. This suggests that overwintered workers do most of a colony's work and that the division of labor among overwintered ants is the more important one under natural conditions. The basis of this division is as yet unknown. These results also suggest that small colony size, univoltine brood schedule and a close association between foraging and brood care do not preclude division of labor among specialized castes, as has been suggested for another ponerine species (Traniello 1978).     

Mechanisms of dispersed central-place foraging in polydomous colonies of the Argentine ant

Many species of ants occupy multiple nests, a condition known as polydomy. Because of their decentralized structure, polydomous colonies may be removed from some of the constraints associated with classic central-place foraging. We used laboratory and field experiments to assess the mechanisms involved in dispersed central-place foraging in polydomous colonies of the Argentine ant Linepithema humile, a widespread invasive species. Both in the laboratory and in the field, Argentine ants established new nests at sites located near food. Laboratory colonies of L. humile redistributed workers, brood and resources among nests in response to the spatial heterogeneity of food resources. In addition, laboratory colonies formed recruitment trails between nests in the context of foraging, providing a mechanism for the transport of material between nests. This highly flexible system of allocating nests, workers and brood throughout a colony's foraging area potentially increases foraging efficiency and competitive ability. The importance of polydomy as a determinant of competitive ability is underscored by its prevalence among ecologically dominant ants, including most, if not all, highly invasive species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Division of Labor Associated with Brood Rearing in the Honey Bee: How Does It Translate to Colony Fitness?

Division of labor is a striking feature observed in honey bees and many other social insects. Division of labor has been claimed to benefit fitness. In honey bees, the adult work force may be viewed as divided between non-foraging hive bees that rear brood and maintain the nest, and foragers that collect food outside the nest. Honey bee brood pheromone is a larval pheromone that serves as an excellent empirical tool to manipulate foraging behaviors and thus division of labor in the honey bee. Here we use two different doses of brood pheromone to alter the foraging stimulus environment, thus changing demographics of colony division of labor, to demonstrate how division of labor associated with brood rearing affects colony growth rate. We examine the effects of these different doses of brood pheromone on individual foraging ontogeny and specialization, colony level foraging behavior, and individual glandular protein synthesis. Low brood pheromone treatment colonies exhibited significantly higher foraging population, decreased age of first foraging and greater foraging effort, resulting in greater colony growth compared to other treatments. This study demonstrates how division of labor associated with brood rearing affects honey bee colony growth rate, a token of fitness.     

Flexible task allocation and the organization of work in ants

Flexibility in task performance is essential for a robust system of division of labour. We investigated what factors determine which social insect workers respond to colony-level changes in task demand. We used radio-frequency identification technology to compare the roles of corpulence, age, spatial location and previous activity (intra-nest/extra-nest) in determining whether worker ants (Temnothorax albipennis) respond to an increase in demand for foraging or brood care. The less corpulent ants took on the extra foraging, irrespective of their age, previous activity or location in the nest, supporting a physiological threshold model. We found no relationship between ants that tended the extra brood and corpulence, age, spatial location or previous activity, but ants that transported the extra brood to the main brood pile were less corpulent and had high previous intra-nest activity. This supports spatial task-encounter and physiological threshold models for brood transport. Our data suggest a flexible task-allocation system allowing the colony to respond rapidly to changing needs, using a simple task-encounter system for generalized tasks, combined with physiologically based response thresholds for more specialized tasks. This could provide a social insect colony with a robust division of labour, flexibly allocating the workforce in response to current needs.     

Foraging for Work and Age-Based Polyethism: The Roles of Age and Previous Experience on Task Choice in Ants

In social insects, colonies commonly show temporal polyethism in worker behavior, such that a worker follows a predictable pattern of changes between tasks as it ages. This pattern usually leads from workers first doing a safe task like brood care, to ending their lives doing the most dangerous tasks like foraging. Two mechanisms could potentially underlie this pattern: (1) age‐based task allocation, where the aging process itself predisposes workers to switch to more dangerous tasks; and (2) foraging for work, where ants switch to tasks that need doing from tasks which have too many associated workers. We tested the relative influence of these mechanisms by establishing nests of Camponotus floridanus with predetermined combinations of workers of known age and previous task specialization. The results supported both mechanisms. Nests composed of entirely brood‐tending workers had the oldest workers preferentially switching to foraging. However, in nests initially composed entirely of foragers, the final distribution of tenders and foragers was not different from random task‐switching and therefore supportive of foraging for work. Thus, it appears that in C. floridanus there is directionality to the mechanisms of task allocation. Switching to more dangerous tasks is age‐influenced, but switching to less dangerous tasks is age‐independent. The results also suggest that older workers are more flexible in their task choice behavior. Younger workers are more biased towards choosing within‐nest tasks. Finally, there are effects of previous experience that tend to keep ants in familiar tasks. Task allocation based on several mechanisms may balance between: (1) concentrating the most worn workers into the most dangerous tasks; (2) increasing task performance levels; and (3) maintaining behavioral flexibility to respond to demographic perturbations. The degree to which behavior is flexible may correlate to the frequency of such perturbations in a species.     

Foraging behavior and recruitment of red imported fire ant Solenopsis invicta Buren in typical habitats of South China

The foraging behavior consisted of three steps: searching, recruitment and transportation. Searching time was different for different foods; searching time for honey was longer than that for any other food tested. It was also affected by habitats with the searching time of fire ants in a litchi orchard being significantly longer than that for other habitats (p<0.01). However, the weight of the food had no obvious effect on the searching time. The recruitment of fire ant workers during foraging was regular, and there was a strong relationship between the number of recruited workers and the transportation time. When the food was too heavy to transport immediately into the nest, the number of recruited workers was maximum at 30 min after the food was initially found. For smaller sized food sources maximum recruitment of workers was possible at a shorter time and the food was more rapidly transported back to the nest. For different foods, the dynamics of recruitment were similar although the number of recruits was different. The weight of the food and the habitats also deeply affected the time spent on transportation.     

Foraging behavior and recruitment of red imported fire ant Solenopsis invicta Buren in typical habitats of South China

The foraging behavior consisted of three steps: searching, recruitment and transportation. Searching time was different for different foods; searching time for honey was longer than that for any other food tested. It was also affected by habitats with the searching time of fire ants in a litchi orchard being significantly longer than that for other habitats (p<0.01). However, the weight of the food had no obvious effect on the searching time. The recruitment of fire ant workers during foraging was regular, and there was a strong relationship between the number of recruited workers and the transportation time. When the food was too heavy to transport immediately into the nest, the number of recruited workers was maximum at 30 min after the food was initially found. For smaller sized food sources maximum recruitment of workers was possible at a shorter time and the food was more rapidly transported back to the nest. For different foods, the dynamics of recruitment were similar although the number of recruits was different. The weight of the food and the habitats also deeply affected the time spent on transportation.     

Observations onApoica pallens,a nocturnal neotropical social wasp (Hymenoptera: Vespidae,Polistinae, Epiponini)

Summary Colonies and nests ofApoica pallens in the llanos region of Venezuela range from small foundress nests to large mature colonies. Nests are sited on small diameter, near-horizontal branches in a variety of shrub and tree species. During the day, adult wasps cluster on the face of the nest in an array that seems to be determined by orientation to gravity; defense of the colony against parasitoids and ants by the resting wasps may be more a passive than an active behavior. Wasps fan their wings to cool the colony during the day, but no foraging for water accompanies the fanning behavior. Nightly foraging activity begins with the explosive departure from the nest of hundreds of wasps, most of which rapidly return. Moderate foraging levels early at night give way to very low foraging levels in pre-dawn hours. The period of moderate foraging may be extended for longer hours during increased moonlight. Foraging wasps collect arthropod provisions for larvae. Larvae produce a trophallactic saliva; adults engage in inter-adult trophallaxis; brood are cannibalized. During cluster formation prior to swarm emigration, adult wasps do not appear to scent-mark substrates such as leaves. Instead,A. pallens exhibits a calling behavior, unique among polistine wasps studied to date, in which the gaster is held rigidly away from the thorax and metasomal sternal glands are exposed. Swarms can emigrate during the day.A. pallens may incorporate absconding and colony relocation as features of its colony cycle in the highly seasonal llanos.     

A field experiment on the influence of load transportation and patch distance on the locomotion velocity of <Emphasis Type="Italic">Dorymyrmex goetschi</Emphasis> (Hymenoptera,Formicidae)

Summary Locomotion velocity during foraging activities is determined by factors such as travel distance, habitat structure and load mass among others. However, few studies on foraging behavior have analyzed the influence of spatial heterogeneity and food transportation on the locomotion velocity of ants under natural conditions. In order to study the mentioned factors, we selected 20 nests of the ant Dorymyrmex goetschi (subfamily Dolichoderinae), in a lower Andes locality of central Chile. Half of the nests were offered a food patch located at 10 cm from the nest entrance, and at 20 cm for the other half. We measured the duration of trips between nest and food patch and vice versa, and the distances traveled. We also recorded spatial heterogeneity of the substratum and soil temperature. Temperature was used as a covariate in the statistical analysis. Travel speed was significantly slower when worker ants returned to the nest with a food load, compared to the velocity of foragers without load that traveled from the nest to the patch. When the food patch was located at greater distance, locomotion velocity was significantly faster. Spatial heterogeneity did not affect movement speed. The reduction in locomotion velocity in ants carrying a load of 5.6 mg represents an energetic cost of transportation equivalent to 79% of the costs involved in moving a body mass of 1.6 mg. Faster velocities at larger patch distances can be interpreted as a strategy to maintain an efficient resource exploitation, by way of decreasing the time exposed to higher predation risk.Received 28 April 2003; revised 11 November 2003; accepted 22 January 2004.     

Ecology and behavior ofGnamptogenys horni (Formicidae: Ponerinae)

Summary In order to examine social behavior in the little-studied ponerine ant genusGnamptogenys, detailed observations were made on captive colonies ofG. horni. Compilation of a behavioral repertory gave evidence of age-based division of labor, with old ants more likely to forage and young ants more likely to tend brood. Workers were observed to line the walls of their nests with pieces of old cocoons, a behavior referred to as wallpapering and previously known from only one other ant species. Evidence was obtained for the use of trail recruitment pheromones in foraging and in nest-moving. Examination of prey remains in natural nests indicated thatG. horni feeds principally on a wide variety of ants, but also on other arthropods.     

Lethal and sublethal effects of thiacloprid on non-target carpenter ant,Camponotus japonicus Mayr (Hymenoptera: Formicidae)

To control population of Monochamus beetles that transmit pine wood nematode, Bursaphelenchus xylophilus, a variety of insecticides have been applied to forest ecosystems in Korea. Non-target predatory insects can be directly or indirectly exposed to insecticides. We evaluated potential lethal and sublethal effects of thiacloprid on survival and behavior of carpenter ants, Camponotus japonicus Mayr. Field-collected ants were directly exposed to several food items such as thiacloprid-exposed Monochamus beetles, 10% sugar water with thiacloprid concentrations, and 10% sugar water at group and individual levels. In experiment for groups of individuals, dead beetle bodies generally had possible adverse effects on ants through dietary exposure, because two forager ants were dead or paralysis after they were exposed to thiacloprid-exposed Monochamus beetles. At individual level, dietary exposure to thiacloprid at concentrations of 10 and 50?mg/L was lethal to ants, causing paralysis and impaired walking. Mortality of ant workers was higher in direct or indirect exposure treatments than that in the control. Some ants exposed to thiacloprid showed abnormal behavior within a few days, especially at thiacloprid concentrations of 10 and 50?mg/L. However, some of them sometimes recovered from the abnormal behavior in a day. In consequence, application of thiacloprid in pine forests may disrupt species interaction and foraging behavior of ants, but the effect of thiacloprid through trophallaxis behavior should be further assessed using more extensive colonies composed of queen, workers, brood, and so on.     

Predation of army ants by Toppin’s titi monkey, <Emphasis Type="Italic">Plecturocebus toppini</Emphasis> Thomas 1914 (Primates: Pitheciidae), in an urban forest fragment in eastern Acre,Brazil

The predation of army ants (Eciton rapax) was recorded during an observational study of the feeding behavior of a group of titi monkeys (Plecturocebus toppini) in an urban fragment of forest in Acre, Brazil. During one observed event, the group’s adult female used its tail to retrieve ants, a type of behavior not observed previously in this genus. All incidents of on-forest floor foraging occurred during the dry season, when fruit was least abundant in the forest, while on other occasions, the ants were captured from tree branches and leaves. The observation of predation and ground-level foraging recorded in this study reinforce the adaptive capacity of P. toppini for survival in fragmented forests, and this was also the first record of the predation of army ants by this titi species.     

Division of labour and specification of castes in the red imported fire ant Solenopsis invicta buren

Division of labour in Solenopsis invicta follows a familiar pattern: younger, smaller ants tend toward brood care while older, larger ants tend toward foraging. However, long-term observations of marked individuals reveal that length of nursing and foraging ‘careers’ and the age of transition between these activities vary considerably between and within size groups, and are related to length of life. Experiments with entire colonies show that larger ants are more likely than smaller ants to forage for insect prey. There are two main worker castes, ‘nurses’ and ‘foragers’, whose members span a wide age-size range, and a large ‘reserve’ subcaste, heterogeneous in age, size, and behaviour: reserves may nurse, forage, store liquid food, or relay food from nurses to foragers. The proportion of ants engaged in foraging decreases with colony size because many ants in large colonies are not exposed to recruitment signals.     

Optimization, conflict, and nonoverlapping foraging ranges in ants

An organism's foraging range depends on the behavior of neighbors, the dynamics of resources, and the availability of information. We use a well-studied population of the red harvester ant Pogonomyrmex barbatus to develop and independently parameterize models that include these three factors. The models solve for an allocation of foraging ants in the area around the nest in response to other colonies. We compare formulations that optimize at the colony or individual level and those that do or do not include costs of conflict. Model predictions were compared with data collected on ant time budgets and ant density. The strategy that optimizes at the colony level but neglects costs of conflict predicts unrealistic levels of overlap. In contrast, the strategy that optimizes at the individual level predicts realistic foraging ranges with or without inclusion of conflict costs. Both the individual model and the colony model that includes conflict costs show good quantitative agreement with data. Thus, an optimal foraging response to a combination of exploitation and interference competition can largely explain how individual foraging behavior creates the foraging range of a colony. Deviations between model predictions and data indicate that colonies might allocate a larger than optimal number of foragers to areas near boundaries between foraging ranges.