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.     

Specializations of birds that attend army ant raids: An ecological approach to cognitive and behavioral studies

Tropical birds forage at army ant raids on several continents. Obligate foraging at army ant raids evolved several times in the Neotropical true antbird family (Thamnophilidae), and recent evidence suggests a diversity of bird species from other families specialize to varying degrees on army ant exploitation. Army ant raids offer access to high prey densities, but the ant colonies are mobile and widely spaced. Successful army ant exploitation requires solving a complex foraging problem because army ant raids are unpredictable in space and time. Birds can counteract the challenges posed by the ants by using strategies that raise their chances of detecting army ant raids, and birds can use additional strategies to track army ant colonies they have located. Some features of army ant biology, such as their conspicuous swarms and columns, above-ground activity, and regular cycles of behavior, provide opportunities for birds to increase their effectiveness at exploiting raids. Changes in sensory, cognitive and behavioral systems may all contribute to specialized army ant exploitation in a bird population. The combination of specializations that are employed may vary independently among bird species and populations. The degree of army ant exploitation by birds varies geographically with latitude and elevation, and with historical patterns such as centers of distribution of obligate thamnophilid antbirds. We predict the set of specializations a given bird population exhibits will depend on local ecology, as well as phylogenetic history. Comparative approaches that focus on these patterns may indicate ecological and evolutionary factors that have shaped the costs and benefits of this foraging strategy. The development of army ant exploitation in individual birds is poorly understood, and individual expression of these specializations may depend on a combination of genetic adaptation with cognitive plasticity, possibly including social and experiential learning. Future studies that measure developmental changes and quantify individual differences in army ant exploitation are needed to establish the mechanisms underlying this behavior.     

Balancing organization and flexibility in foraging dynamics

Proper pattern organization and reorganization are central problems facing many biological networks which thrive in fluctuating environments. However, in many cases the mechanisms that organize system activity oppose those that support behavioral flexibility. Thus, a balance between pattern organization and pattern flexibility is critically important for overall biological fitness. We study this balance in the foraging strategies of ant colonies exploiting food in dynamic environments. We present discrete time and space simulations of colony activity that uses a pheromone-based recruitment strategy biasing foraging towards a food source. After food relocation, the pheromone must evaporate sufficiently before foraging can shift colony attention to a new food source. The amount of food consumed within the dynamic environment depends non-monotonically on the pheromone evaporation time constant—with maximal consumption occurring at a time constant which balances trail formation and trail flexibility. A deterministic, ‘mean field’ model of pheromone and foragers on trails mimics our colony simulations. This reduced framework captures the essence of the flexibility-organization balance, and relates optimal pheromone evaporation to the timescale of the dynamic environment. We expect that the principles exposed in our study will generalize and motivate novel analysis across a broad range systems biology.     

Ambush Predation of Stingless Bees (<Emphasis Type="Italic">Tetragonisca angustula</Emphasis>) by the Solitary-Foraging Ant <Emphasis Type="Italic">Ectatomma tuberculatum</Emphasis>

Social insect colonies are high-value foraging targets for insectivores, prompting the evolution of complex colony defensive adaptations as well as specialized foraging tactics in social insect predators. Predatory ants that forage on other social insects employ a diverse range of behaviors targeted at specific prey species. Here, we describe a solitary foraging strategy of the ant Ectatomma tuberculatum, on nest guards of the stingless bee Tetragonisca angustula. We observed multiple instances of E. tuberculatum ambushing and successfully capturing the hovering and standing guards of T. angustula near nest entrances. The unique hovering behavior of the guard caste of this bee species, an adaptation to frequent cleptoparasitism by other stingless bees, may make these guards particularly vulnerable to ground-based, ambush attacks by E. tuberculatum. Likewise, the behavior of the foraging ants appears to adaptively exploit the defensive formations and activity patterns of these bees. These observations suggest an adaptive and targeted predatory strategy aimed at gathering external guard bees as prey from these heavily fortified nests.     

Assessing Microhabitat Cover and Distance Effects on Harvester Ant Intraspecific Seed Preference

Harvester ants have long been known to exhibit interspecific seed preference and this preference has been thought to be associated with distance in a manner analogous with optimal foraging theory. However, little attention has been given to how intraspecific seed preference changes or how microhabitat (i.e. the composition of the terrain that the ants are moving through) impacts seed harvesting preference. We addressed these questions by conducting seed harvesting experiments in three different Ephedra viridis populations that contain harvester ants (Pogonomyrmex occidentalis) by using only E. viridis seeds and conducting trials over multiple distances and varying degrees of microhabitat cover. We found that increased microhabitat cover and increased seed mass decrease the likelihood of E. viridis seeds being harvested much more dramatically than distance. However, we found no effect of distance or microhabitat cover on which E. viridis seeds were harvested. We conclude that harvester ant E. viridis seed preference is distance and microhabitat independent. However, increases in microhabitat cover negatively impacts the likelihood of P. occidentalis harvesting E. viridis seeds of any size. Our findings suggest that harvester ant foraging behavior is influenced by structure of the microhabitat more than by distance. This provides a new context on how harvester ant foraging behavior and effectiveness should be considered.     

Spatial Distribution and Fruiting Phenology of Protium heptaphyllum (Burseraceae) Determine the Design of the Underground Foraging System of Atta sexdens L. (Hymenoptera: Formicidae)

Leaf-cutting ants have long been recognized to forage via complex trail systems but the nature and the ecological drivers of the different foraging strategies adopted remain a key topic. Here, we described the spatiotemporal use of belowground foraging galleries by Atta sexdens L. in the Brazilian Atlantic forest, and examined the adaptive advantages of this foraging strategy. Protium heptaphyllum adult trees (DBH?>?10?cm), seed/seedling clumps and ant gallery entrances were mapped across two 1-ha plots during two consecutive fruiting seasons (2002 and 2004). We recorded 75 ca. 40?cm deep gallery entrances beneath 26 P. heptaphyllum trees at nest distances ranging from 14 to 57?m. Furthermore, gallery abundance and galleries associated with seed/seedling clumps correlated positively with P. heptaphyllum density. Our results indicate that A. sexdens was able to set a permanent system of underground galleries targeting P. heptaphyllum trees and their seeds on the ground. Such network of galleries was spatially arranged according to both the spatial distribution and abundance of P. heptaphyllum trees in a way that most gallery entrances were disposed beneath or in close periphery of P. heptaphyllum crowns. Our findings suggest that underground trail systems shaped by fruit resources represent a foraging strategy clearly more common than existing literature on the subject would suggest. In addition, it reinforces the notion that the spatiotemporal availability of resources combined with predation risk largely influence trail configurations as well as overall foraging strategies adopted by leaf-cutting ants.     

Spatio-temporal Foraging Dynamics in Two Coexisting Harvester Ants (Hymenoptera: Formicidae)

Different aspects of the foraging strategies of two harvester ant species, Messor wasmanni and M. minor, were investigated in a Mediterranean dry grassland area. Baits were used to evaluate the existence of a trade-off between resource discovery and domination as well as the effect of three variables (air temperature, relative humidity and distance) on the trade-off. Baits were also utilized to explore random vs non random use of time by colonies. Random vs non random utilization of space was instead evaluated by mapping the daily foraging area of colonies in a grid of 900 plots of 1 m² each. Results revealed that species coexistence is not preferentially supported by a trade-off in resource utilization with no overall effect of the examined variables. The foraging activity of the two species widely overlapped whilst a clear competition for space occurred. The observed space partitioning could represent an advantageous strategy for the coexistence of the two ant species.     

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.     

Foraging activity of leaf-cutter ants is affected by barometric pressure

Among all activities displayed by ant colonies, searching for food is essential for all individuals survival. However, many external activities are hazardous or restrictive for the entire society. Even though leaf-cutter ants are highly successful insects, they are subject to extreme aspects of foraging, as raindrops and wind. Although recruitment and food exploitation are known to change with temperature and humidity, barometric pressure changes and how they affect ant behavior remain unknown. We aimed to determine how an increase or decrease in barometric pressure might modify foraging strategies of the leaf-cutter ant Atta sexdens compared to steady pressure. The first modification observed in the workers behavior was the scouts greater promptness in leaving the nest when the barometric pressure decreased. Regard to the foragers, there was no difference in the number of individuals recruited for collecting leaves. However, it was cut and brought into the nest 1.5 and 2 times more leaves during the pressure drop, respectively. The reason for this foraging efficiency as a whole was ultimately the sum of the efficiency of each forager. The shifts in behavior, therefore, could be related to the indirect consequences of a pressure decrease, such as rainfall and strong winds, both strong constraints on ants on a trail. This is the first report of barometric pressure affecting the behavior of a social insect under controlled conditions.     

Olfactory behavior and response of household ants (Hymenoptera) to different types of coffee odor: A coffee-based bait development prospect

Odor sensation is a sensory modality of considerable significance in the foraging behavior and interactional organization of ants. In the food bait technology, smell is the basis of attraction, which, in turn, is the line of bait use and a key parameter for judging efficacy. Yet, the currently available baits possess low attractiveness to many ant pests. Hence, strategies to produce ant bait with increased attractiveness are needed. Despite evidence that coffee has a diverse aroma complex that affects the behavior of honey bees and ants, its attraction to house-invading ants has yet to be investigated. In a series of Y-tube olfactometer bioassays, we examined the behavioral responses of Tapinoma indicum (TI), Monomorium pharaonis (MP) and Solenopsis geminata (SG) to various coffee-induced odor stimuli, comprised of extracts from Arabica, Robusta and Liberica. All coffee extracts showed an influence on the behavior of TI, MP and SG workers, with Arabica showed the most significant influence to the tested ants. The workers of TI, MP and SG were more attracted to the odor of 0.01% Arabica extract (ONE), in comparison with 0.05% Arabica extract (TWO) or 0.10% Arabica extract (THREE). Arabica extract mixed with sugar (S) elicited a significant attraction from workers of all three species in a balanced competition with either unsweetened Arabica extract or water. These results indicated that coffee, particularly Arabica, was attractive to the foragers of TI, MP and SG, thus, the use of coffee as a novel stimulus agent seems plausible in ant bait development.     

Plant design and non-random foraging by ants on Croton bonplandianum Baill. (Euphorbiaceae)

Croton bonplandianum bears female flowers in inflorescences which are arranged in a regular pattern. Foraging individuals of the ant Camponotus sericius feed on the nectar in the nectary glands of female flowers. The pattern of movement of ants while foraging between these regularly placed inflorescences was highly systematic and distinctly exploratory. The ants tended to visit new inflorescences at each move and avoided revisiting inflorescences. They followed this foraging pattern by adopting circular movements either to the left or to the right and avoiding other complex but equally effective moves. This was probably due to memory constraints. The ants predicted the resource quality of the subset of a patch by sampling a part of it. The inflorescences within a cluster were similar in quality. Using this relation ants could make decisions about continuing to forage in a cluster after sampling any one inflorescence. If the first inflorescence visited was of poor quality they abandoned the cluster. This ensured efficient foraging with minimal expenditure of time and energy.     

Bees do not use nearest-neighbour rules for optimization of multi-location routes

Animals collecting patchily distributed resources are faced with complex multi-location routing problems. Rather than comparing all possible routes, they often find reasonably short solutions by simply moving to the nearest unvisited resources when foraging. Here, we report the travel optimization performance of bumble-bees (Bombus terrestris) foraging in a flight cage containing six artificial flowers arranged such that movements between nearest-neighbour locations would lead to a long suboptimal route. After extensive training (80 foraging bouts and at least 640 flower visits), bees reduced their flight distances and prioritized shortest possible routes, while almost never following nearest-neighbour solutions. We discuss possible strategies used during the establishment of stable multi-location routes (or traplines), and how these could allow bees and other animals to solve complex routing problems through experience, without necessarily requiring a sophisticated cognitive representation of space.     

The Effects of the Conversion of a Primary to a Secondary Tropical Lowland Forest on Bullet ant (Paraponera clavata) Foraging Behavior in Costa Rica: A Possible Indicator of Ecosystem Condition

The use of bioindicators of habitat condition can help to better understand the effects of tropical forest degradation and the efficacy of strategies used in the restoration of these lands. The differences in feeding behavior of the ponerine ant Paraponera clavata may serve as such an indicator. The findings from the current study showed that P. clavata in an undisturbed primary forest returned to the nest with prey, nectar, and plant materials, while none of the ants within a 14 year old regenerating secondary forest returned with prey or nectar, few with plant materials, and most of the returns were unsuccessful in their foraging. This suggests a difference in P. clavata feeding behavior and/or food selection is occurring in the disturbed habitat; that P. clavata from the primary forest nest examined in the current study are feeding at a higher trophic level; and that the ants in the primary forest appeared to be more successful and efficient foragers than those in the secondary forest. Future studies should involve more comparisons of P. clavata foraging behavior in secondary to primary forests to determine if the patterns described in this current study are consistent with disturbance in these tropical forests in order to evaluate the possibility of this use of P. clavata as a valuable tool for bioindicators of habitat damage.     

Social predation by ants as a mortality source for an arboreal gregarious forest pest

Biocontrol of caterpillars by ants is highly variable, and we investigate how the strength of the trophic relationship between ants and an important outbreaking forest pest depends on phenological synchrony and on social foraging. We test the hypothesis that early spring foraging by ants, coupled with eusocial recruitment behavior, could undermine the caterpillar's strategies to achieve either enemy-free space or predator satiation.We use a series of field surveys and experiments in trembling aspen stands (Populus tremuloides) in the boreal forest of eastern Canada to assess the role of ants in early-instar mortality of the outbreaking, gregarious forest tent caterpillar (Malacosoma disstria). We also investigate individual-level mechanisms related to phenology and social behavior that underlie the effectiveness of ants as biocontrol on caterpillars. Our results show that ants climb trees early in the spring and harvest young forest tent caterpillars, suggesting that early phenology does not provide an entirely enemy-free space for caterpillars. Our findings further show that recruitment-based social foraging enables ants to deplete groups of gregarious prey, suggesting that these eusocial insects are particularly effective at generating predation pressure on gregarious herbivores since they do not satiate easily. Finally, a manipulative predator exclusion experiment confirms that ant predation is a significant mortality source for early-instar forest tent caterpillars. Taken together, these results suggest that phenology and sociality could modulate the role of ants as effective caterpillar predators and thus showcase the importance of considering natural history and behavioral traits when studying trophic interactions and their role in population dynamics.     

Effect of constant and fluctuating temperature on the circadian foraging rhythm of the red imported fire ant,Solenopsis invicta Buren (Hymenoptera: Formicidae)

Understanding circadian foraging rhythms activity of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae) foragers at different temperatures is an important step towards developing control measures in Integrated Pest Management (IPM) programs. In this study, the circadian foraging rhythm activities of S. invicta foragersat different temperature were investigated under laboratory and field conditions. Results indicated that the foraging activity increased after sunrise, and maximum foraging occurred at 14:00 (foraging rate was 69.22 ± 0.57 and 72.58 ± 1.15 foragers/min in the first and second year, respectively) in the tea fields of Guangzhou during autumn. Furthermore, foragers demonstrated circadian rhythms and exhibited a unimodal after 24 h. A significant correlation was found between foraging activity and temperature. S. invicta colonies were active at moderate soil temperatures (approximately 26.65 °C to 29.24 °C). The preferred temperature of the colonies was 26 °C, followed by 22 °C and 18 °C in the laboratory. The individual S. invicta activity was maximum at 17:00 (18.67 ± 1.66 times /10 min) and minimum at 5:00 (8.33 ± 2.51 times/10 min) at 26 °C. The fluctuating temperature had a significant impact on individual locomotor activity (r = 0.8979, P < 0.01) but did not alter the rhythm activity. Our results demonstrated that temperature might play an important role in circadian foraging rhythms activity of S. invicta. These results may have implications for the development of more effective fire ant management strategies.     

Experimental investigation of information transmission in Formica pratensis (Hymenoptera, Formicidae) using “binary tree” maze

Organization of foraging and information transmission in the ant Formica pratensis were studied using the “binary tree” maze. The ants were shown to use distant homing. They were able to memorize and transmit up to four bits of information. The foraging mode was shown to depend on the colony size: an increase in the number of ants was accompanied by switching from solitary to group foraging. A relay mode of information transfer (an ant relays the information to several others, etc.) was revealed. The organization of work and information flows in the colonies of Formica polyctena and F. pratensis were found to be essentially different. The communicative systems in dominant ant species are variable and species-specific.     

Intraspecific Thievery in the Ant Ectatomma ruidum is Mediated by Food Availability

Animals modify their foraging strategies in response to environmental changes that affect foraging performance. In some species, cleptobiosis represents an alternative strategy for resource access. The environmental factors that favor the incidence or prevalence of cleptobiosis, however, are poorly described. The cleptobiotic Neotropical ant Ectatomma ruidum is characterized by a high frequency of thievery behavior, a specific type of intraspecific cleptobiosis, in which specialized thief workers insinuate themselves into nests of neighboring colonies and intercept food items brought into these nests. Here, we evaluate how colonies adjust thievery behavior in response to food availability. We supplemented food availability and measured how the incidence and intensity of thievery responded to resource availability. We found that the incidence and intensity of thievery decline in response to supplemental food, suggesting that thievery behavior is a response to resource limitation at the population scale. This finding indicates that the phenomenon of intraspecific thievery, although a rare strategy in among colonies of social animals, is a viable alternative foraging tactic in the context of competition and food limitation.     

Reliability theory and foraging by ants

Reliability theory is used to explore the consequences of ant colony's foraging techniques for the evolution of individual competence. Five fundamental strategies are outlined according to Oster & Wilson (1978) and corresponding probabilities of food being returned to the nest are derived. The strategies differ in redundancy schemes and levels of worker reliability. Colony-level selection produces workers of imperfect competence. System reliability can be very high even when the workers are inept, if the foraging strategy is complex and redundant. Individual competence of foragers in a colony depends on diet breadth, caste polymorphism, and tempo. The implications of each variable for colony survival are discussed.     

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.     

Foraging behavior and morphology: seed selection in the harvester ant genus, Pogonomyrmex

Optimally foraging animals can be behaviorally or morphologically adapted to reduce the energetic and time costs of foraging. We studied the foraging behavior and morphology of three seed harvester ant species, Pogonomyrmex barbatus, P. desertorum, and P. occidentalis, to determine the importance of behavioral strategies and morphological features associated with load carriage in reducing the costs of foraging. We found that none of five morphological features we measured had a significant impact on seed selection. Also, body size did not influence running speed, an important variable in time costs of foraging. Temperature had the largest effect on running speed in these species. Our results show that these species have foraging strategies which minimize the time costs of traveling with seeds. We also describe a pattern where the running speed in individual-foraging species is less affected by increasing seed size than in trunk-trail foragers, when temperature and body mass are held constant. These results support previous work which showed that time costs are most important in seed selection for Pogonomyrmex, and suggest that central place foraging theory may need to accommodate variation in foraging strategy to more accurately predict optimal seed size selection in harvester ants. Received: 16 June 1997 / Accepted: 15 December 1997