Temporal relationships of rubbing behavior with foraging and petiole enlargement inParapolybia indica (Hymenoptera: Vespidae)

Summary The frequency of application of ant repellent secreted from the metasomal sternum VI gland to the nest petiole (=rubbing behavior) inParapolybia indica colonies decreased significantly from the preemergence, single-foundress stage to the post-emergence stage. In the pre-emergence stage, rubbing occurred in close temporal association with the departure from the nest, which may maximize the antrepelling effect of the rubbing substance during the period when the nest is not attended by any wasps. On the other hand, only a small proportion of the departures was associated with rubbing in the post-emergence stage.Unlike in other independent-founding polistine wasps, rubbing inP. indica was not associated with petiole enlargement. Among independent-founding polistines,P. indica is unusual in that females enlarge the nest petiole with a large amount of plant fibers instead of strict use of adult saliva, and in that the petiole surface is rough, and may be much more absorbent than that of the secretion petiole. On the other hand, in the species showing a temporal association between petiole enlargement and rubbing, females typically rub immediately after petiole licking (application of oral secretion). This fact, and the lack of such a temporal association inP. indica, may suggest a possibility that the mixture of oral secretion and rubbing substance on the smooth surface of the secretion petiole makes the chemical barrier last longer.     

A latitudinal gradient in intensity of applying ant-repellent substance to the nest petiole in paper wasps (Hymenoptera: Vespidae)

Summary Observations on pre-emergence, single-foundress colonies of Japanese paper wasps (Polistes) revealed that there was a latitudinal gradient in intensity of application of an ant-repellent substance (secreted by the metasomal sternum VI glands) to the nest petiole. Thus the lower the latitude, the more frequently a foundress rubbed ant repellent onto the nest petiole. Estimation of potential ant predation on wasp brood using bait traps showed that there was a positive correlation between the frequency of rubbing and potential predation pressure from ants which are guided predominantly by substrate cues for foraging. There was also a latitudinal gradient in the degree of temporal association of rubbing behavior with foraging: the lower the latitude, the more closely foundress departure from the nest was associated with rubbing. Enlargement of the nest petiole by applying oral secretion potentially obliterated previous coats of ant repellent; however, this behavior was not always followed by rubbing behavior. The ant-repellent chemical barrier around the nest petiole may have evolved in tropical regions of the world as a defense against ant predation on wasp brood. I argue that as ant predation pressure diminishes towards the cooler regions, so does selection maintaining the behavioral sequence where foundress departure from the nest is preceded by rubbing behavior.     

Nest raiding by the invasive Argentine ant on colonies of the harvester ant, Pogonomyrmex subnitidus

Invasive ants often displace native ants, and published studies that focus on these interactions usually emphasize interspecific competition for food resources as a key mechanism responsible for the demise of native ants. Although less well documented, nest raiding by invasive ants may also contribute to the extirpation of native ants. In coastal southern California, for example, invasive Argentine ants (Linepithema humile) commonly raid colonies of the harvester ant, Pogonomyrmex subnitidus. On a seasonal basis the frequency and intensity of raids vary, but raids occur only when abiotic conditions are suitable for both species. In the short term these organized attacks cause harvester ants to cease foraging and to plug their nest entrances. In unstaged, one-on-one interactions between P. subnitidus and L. humile workers, Argentine ants behaved aggressively in over two thirds of all pair-wise interactions, despite the much larger size of P. subnitidus. The short-term introduction of experimental Argentine ant colonies outside of P. subnitidus nest entrances stimulated behaviors similar to those observed in raids: P. subnitidus decreased its foraging activity and increased the number of nest entrance workers (many of which labored to plug their nest entrances). Raids are not likely to be the result of competition for food. As expected, P. subnitidus foraged primarily on plant material (85% of food items obtained from returning foragers), but also collected some dead insects (7% of food items). In buffet-style choice tests in which we offered Argentine ants food items obtained from P. subnitidus, L. humile only showed interest in dead insects. In other feeding trials L. humile consistently moved harvester ant brood into their nests (where they were presumably consumed) but showed little interest in freshly dead workers. The raiding behavior described here obscures the distinction between interspecific competition and predation, and may well play an important role in the displacement of native ants, especially those that are ecologically dissimilar to L. humile with respect to diet. Received 15 July 2005; revised 19 October 2005; accepted 26 October 2005.     

Coordination of Raiding and Emigration in the Ponerine Army Ant Leptogenys distinguenda (Hymenoptera: Formicidae: Ponerinae): A Signal Analysis

Several glandular sources of trail pheromones have been discovered in army ants in general. Nevertheless, at present the understanding of the highly coordinated behavior of these ants is far from complete. The importance of trail pheromone communication for the coordination of raids and emigrations in the ponerine army ant Leptogenys distinguenda was examined, and its ecological function is discussed. The secretions of at least two glands organize the swarming activities of L. distinguenda. The pygidial gland is the source of an orientation pheromone holding the group of raiding workers together. The same pheromone guides emigrations to new nest sites. In addition, the poison sac contains two further components: one with a weak orientation effect and another which produces strong, but short-term attraction and excitement. The latter component is important in prey recruitment and characterizes raid trails. This highly volatile recruitment pheromone allows the extreme swarm dynamic characteristic of this species. Emigration trails lack the poison gland secretion. Due to their different chemical compositions, the ants are thus able to distinguish between raid and emigration trails. Nest emigration is not induced chemically, but mechanically, by the jerking movements of stimulating workers.     

Zombie fire ant workers: behavior controlled by decapitating fly parasitoids

Laboratory observations were conducted on four separate red imported fire ant, Solenopsis invicta, colonies that contained workers parasitized by the decapitating fly, Pseudacteon tricuspis. Parasitized S. invicta workers remained inside the nest during parasitoid larval development and left the nest approximately 8 – 10 hours before decapitation by the parasitoid. When parasitized ants left the nest, they were highly mobile, were responsive to tactile stimuli, and showed minimal defensive behavior. Ants ultimately entered into a grass thatch layer, where they were decapitated and the fly maggots pupariated. This study reveals that parasitized ants exhibit behaviors that are consistent with host manipulation to benefit survival of the parasitoid. Received 9 November 2006; revised 26 January 2007; accepted 7 February.     

Sexual Calling by Workers Using the Metatibial Glands in the Ant, Diacamma sp., from Japan (Hymenoptera: Formicidae)

Several species of the ant genus Diacamma reproduce through mated workers (gamergates). Such gamergates have no wings and therefore are unable to conduct nuptial flight. Instead they perform a sexual calling behavior by standing outside the nest and rubbing the tibiae of their hindleg over the surface of the arched gaster. In a series of exclusion experiments we demonstrate that secretions from the metatibial gland are the most important component in making the virgin female attractive to the males.     

Dispersed central place foraging in Australian meat ants

Summary Australian meat ants often inhabit colonies with widely dispersed nest holes, and this study examines how resource is harvested and distributed in a colony ofIridomyrmex sanguineus Smith (Formicidae: Dolichoderinae). The three principal types of foragers (tenders, honeydew transporters, scavengers) exhibited nest hole fidelity, where harvested resource was consistently delivered to the same nest hole by each foraging individual. Australian meat ants thus use a harvesting system based on dispersed central place foraging. Evidence of frequent larval transport among nest holes, age polyethism developing in the direction of foraging, and the tendency for nest-associated workers to accept new nest holes more readily than foragers, suggests that workers develop fidelity to the particular nest hole in which they eclose. Coupled with larval transport, nest hole fidelity may allow a colony with widely dispersed nest holes to adjust its structure to more efficiently harvest a resource distributed unevenly in space or time.     

Simple rules based on pile slope are used in the self organization of sand pile formation by <Emphasis Type="Italic">Pheidole oxyops</Emphasis> ants

We tested the hypothesis that slope influences where worker ants deposit excavated soil on piles near the nest entrance. We predicted that ants will deposit their load near the top of a pile where the slope changes from upward to downward, to prevent material rolling back towards the entrance. We tested this hypothesis by studying five natural colonies of Pheidole oxyops ants at a field site at S?o Sim?o, Brazil. At this site, each colony was dumping sandy soil excavated from its underground nest in a crescent-shaped pile c. 13 cm from and perpendicular to the nest entrance. Each nest was given an experimental sand pile of symmetrical curved cross section on a plywood platform that could be tilted 15 degrees up or down. From videos, the locations where individual ants dumped their soil loads were measured in relation to the inner (position = 0) and outer (position = 1) edges of the pile. When the platform was tilted down the ants deposited their loads significantly closer to the inner edge (0.458 ± 0.007) than when not tilted (0.530 ± 0.006). When the platform was tilted up the ants deposited their loads significantly further from the inner edge (0.626 ± 0.006) than when not tilted (0.522 ± 0.006). These results support the hypothesis that ants use pile slope in deciding where to dump their load. A similar rule is probably used in other ant species that place excavated soil in steep piles near the nest entrance. Received 5 February 2007; revised 10 June 2007; accepted 9 October 2007.     

Resource Assessment, Recruitment Behavior, and Organization of Cooperative Prey Retrieval in the Ant Formica schaufussi (Hymenoptera: Formicidae)

Foragers of the ant Formica schaufussi recruit nestmates to large anthropod prey and cooperatively transport the prey to the nest. The size of the group of ants retrieving prey is significantly correlated with the prey mass at the point at which the retrieval group reaches the nest entrance. To understand the mechanism involved in this size matching process, the regulation of retrieval group size was investigated by examining the modulatory role of trail pheromones in recruitment communication and the behavioral processes that might adjust retrieval group size to prey mass. Laboratory studies of hindgut, poison, and Dufour's gland extracts showed that the contents of the hindgut, which was determined to be the source of trail pheromone, induced recruitment and orientation behavior in ants and regulated the recruitment response of ants in the absence of any other communication signal. However, chemical mass communication alone did not appear to explain the regulation of retrieval group size. Scout ants assess whether to collect prey individually or recruit nestmates to group-retrieve 100-, 200-, or 400-mg prey but did not vary group size in relation to either the prey mass or the presence of interspecific competitors once the decision to initiate group retrieval was made. The number of recruits leaving the nest was independent of these factors and first matched prey mass during prey transport, possibly through a process of differential individual response to immobile versus mobile prey items. Unpredictable factors such as prey resistance to movement and rapidly changing degrees of interspecific competition may preclude scouts from fine-tuning the retrieval group size before it reaches the prey.     

Speed-versus-accuracy trade-offs during nest relocation in Argentine ants (Linepithema humile) and odorous house ants (Tapinoma sessile)

Animals are often forced to accommodate disturbance to their territories or nests. When nest relocation becomes necessary, it is important to efficiently evaluate alternative nest sites to choose the one most suitable under current conditions. However, if time is limiting, species may experience a speed-versus-accuracy trade-off when searching for a new home. We examined nest site selection under duress (in the form of flooding) in two species of ants: Linepithema humile and Tapinoma sessile. We predicted that if ants are able to assess and evacuate to the most suitable location, colonies should move to higher elevation, relative to their current nest site, in response to flooding. To test for a speed-versus-accuracy trade-off, we presented colonies with new nest chambers that were either higher, lower, or at the same height as their current nest and examined if their ability to efficiently choose a new site was influenced by the rate of flooding. When flooding rates were slow, both species favored the highest nest site and nearly always moved their entire nest to the same chamber. However, when the rate of flooding was doubled, colonies of T. sessile less often chose the highest nest site and were also more likely to split their nests between two of the available chambers. These results demonstrate a trade-off between speed and accuracy in nest site selection for odorous house ants, while L. humile retained their ability to adequately assess new nest sites under the conditions we presented. These patterns may arise from differences in exploratory behavior and activity between the two species. Despite having identical colony sizes, L. humile had approximately ten times more workers exploring the alternate nest sites 30 min into the experiment than did T. sessile.     

Anting in a Semifree-ranging Group of <Emphasis Type="Italic">Cebus apella</Emphasis>

Capuchins apply many organic materials, especially leaves, to their skin. Protection against ectoparasites is the most commonly discussed explanation for the behavior. We describe fur rubbing with carpenter ants(Camponotus rufipes) by semifree-ranging tufted capuchins(Cebus apella) in the Tietê Ecological Park, S?o Paulo, Brazil. Carpenter ants produce and secrete high concentrations of formic acid, which repels tick nymphs. Anting occurred significantly more often during months of seasonal incidence of nymphs of the tick Amblyomma cajennense, and the behavior was not related to ant-eating. We argue that anting behavior in tufted capuchins fits the hypothesis of protection against ectoparasites.     

Early learning of volatile chemical cues leads to interspecific recognition between two ant species

Nestmate recognition in social insects generally involves matching a label to the template that is acquired through the early learning of non-volatile cuticular hydrocarbon cues. However, a possible role of the volatile chemical cues that exist in the nest, and which may also affect template formation, has not been studied. We investigated this possibility using experimental mixedspecies groups composed of the two ant species Manica rubida and Formica selysi. The experimental set-up either allowed full contact between workers of the two species or interspecific contact was hindered or prohibited by a single or a double mesh. After three months, workers of M. rubida ants were selected as focal ants for aggression tests including the following target ants: F. selysi workers from the same mixed-species group (for each of the three rearing conditions) or from a single-species group (control). Workers of M. rubida were always amicable towards their group-mates, irrespective of the experimental group (contact, single or double mesh). However, M. rubida that were not imprinted on F. selysi, expressed high levels of aggression towards the non-familiar F. selysi workers. The finding that F. selysi workers in the mixed-species groups appeared familiar to their M. rubida group-mates even without physical contact between them, suggests that the volatile cues produced by F. selysi affected nestmate recognition in M. rubida. In an attempt to identify these volatile cues we performed SPME analysis of the head space over groups of F. selysi workers. The findings revealed that F. selysi Dufour’s gland constituents, with undecane as the major product, are released into the head space, rendering them likely candidates to affect template formation in M. rubida. Analysis of Dufour’s gland secretion of F. selysi revealed a series of volatile alkanes, including undecane as a major product. These alkanes were not present in the glandular secretion of M. rubida, whose secretion was mainly composed of isomers of farnesene. We therefore hypothesize that callow M. rubida workers in the mixed-species groups had become imprinted by the above alkanes (in particular undecane, being the major heterospecific volatile in the head space) and incorporated them into their own template. Received 18 October 2007; revised 2 January 2008; accepted 7 January 2008.     

Behavioral mechanisms of collective nest-site choice by the ant Temnothorax curvispinosus

This paper examines the individual behavior underlying collective choice among nest sites by the ant Temnothorax (formerly Leptothorax) curvispinosus. Colonies can actively compare options, rejecting a mediocre site when it is paired with a good one, but accepting the same mediocre design if it is instead paired with a worse site. This ability emerges from the behavior of an active minority of workers who organize emigrations. When one of these finds a promising site, she recruits nest mates to it, but only after a delay that varies inversely with site quality. Ants first recruit fellow active ants via slow tandem runs, but eventually switch to speedier transports of the colony’s passive majority. Later transports grow faster still, as ants improve their speed with experience. An ant’s choice of recruitment type is governed by a quorum rule, such that her likelihood of starting to transport increases with the population of the new site. The size of the quorum depends on experience, with ants demanding a larger population to launch immediately into transport than they do to switch to transport after first leading a few tandem runs. Perception of quorum attainment requires direct contact between ants. The ants’ behavior qualitatively matches that of T. albipennis, where models have shown that decentralized choice of the best site depends on quality-dependent recruitment delays, amplified by a quorum rule for initiating transport. Parameter estimates for an agent-based model show significant quantitative differences between the species, and suggest that T. albipennis may place relatively greater emphasis on emigration speed. Received 11 February 2005; revised 10 May 2005; accepted 20 May 2005.     

Nest Defense and Conspecific Enemy Recognition in the Desert Ant Cataglyphis fortis

This study focuses on different factors affecting the level of aggression in the desert ant Cataglyphis fortis. We found that the readiness to fight against conspecific ants was high in ants captured close to the nest entrance (0- and 1-m distances). At a 5-m distance from the nest entrance the level of aggression was significantly lower. As the mean foraging range in desert ants by far exceeds this distance, the present account clearly shows that in C. fortis aggressive behavior is displayed in the context of nest, rather than food-territory defense. In addition, ants were more aggressive against members of a colony with which they had recently exchanged aggressive encounters than against members of a yet unknown colony. This finding is discussed in terms of a learned, enemy-specific label-template recognition process.     

Orientation and Communication in the Neotropical Ant Odontomachus bauri Emery (Hymenoptera,Formicidae, Ponerinae)

The Neotropical species Odontomachus bauri employs canopy orientation during foraging and homing. An artificial canopy pattern above the ants is much more effective as an orientation cue than horizontal landmarks or chemical marks. However, both horizontal visual cues and chemical marks on the ground can serve in localizing the nest entrance. Successful O. bauri foragers recruit nestmates to leave the nest and search for food. However, the recruitment signals do not contain directional information. Antennation bouts and pheromones from the pygidial gland most likely serve as stimulating recruitment signals. Secretions from the mandibular and poison gland elicit alarm and attack behavior.     

Supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes, on an oceanic island: Forager activity patterns, density and biomass

Summary. Ants have the capacity to reach unusually high densities, mostly in their introduced ranges. Numerical dominance is often cited as key to the ability of exotic ants to displace native ant species, reduce the abundance of invertebrates and negatively impact upon bird, land crab and other vertebrate populations. On Christmas Island, Indian Ocean, the yellow crazy ant, Anoplolepis gracilipes (Jerdon), forms supercolonies, where extremely high densities of foraging ants have contributed to ‘invasional meltdown’ in rainforest areas. Densities of up to 2254 foraging ants per m² and a biomass of 1.85 g per m² were recorded, and nest densities reached 10.5 nest entrances per m². Populations of A. gracilipes can overcome and kill red endemic land crabs (Gecarcoidea natalis) over 100 times their own biomass. This is the highest recorded density of foraging ants, and adds another element to the definition of ‘supercolony’ of unicolonial ants. This paper documents one extreme in a continuum of densities of unicolonial, invasive ant species and highlights the need to incorporate forager densities into invasive ant research.Received 17 November 2004; revised 14 February 2005, accepted 21 February 2005.     

Group hunting in a ponerine ant,Leptogenys nitida Smith

Field observations on the emigration and foraging behaviours of the southern African ponerine ant, Leptogenys nitida, were undertaken at Mtunzini, Natal, South Africa. These colonies have a single ergatoid queen and 200–1000 workers. The nest sites are found in the leaf litter and these nests are moved frequently over distances ranging from 0.5 to 5 m. Leptogenys nitida is a diurnal predator of arthropods dwelling in the leaf litter. Up to 500 workers participate in each foraging trail, and are not led by definite scouts. Ants form clear trunk trails and fan out at various intervals to search for prey. The prey is searched for and retrieved cooperatively. From laboratory tests it was determined that ants will follow pygidial gland extracts, with the poison gland extract eliciting a limited response. The type of army ant behaviour observed in L. nitida seems to be different to that observed in other ponerine ants.     

Behavioral Interactions Between <Emphasis Type="Italic">Aphaenogaster rudis</Emphasis> (Hymenoptera: Formicidae) and <Emphasis Type="Italic">Reticulitermes flavipes</Emphasis> (Isoptera: Rhinotermitidae): The Importance of Physical Barriers

Predation pressure from ants is a major driving force in the adaptive evolution of termite defense strategies and termites have evolved elaborate chemical and physical defenses to protect themselves against ants. We examined predator–prey interactions between the woodland ant, Aphaenogaster rudis (Emery) and the eastern subterranean termite, Reticulitermes flavipes (Kollar), two sympatric species widely distributed throughout deciduous forests in eastern North America. To examine the behavioral interactions between A. rudis and R. flavipes we used a series of laboratory behavioral assays and predation experiments where A. rudis and R. flavipes could interact individually or in groups. One-on-one aggression tests revealed that R. flavipes are vulnerable to predation by A. rudis when individual termite workers or soldiers are exposed to ant attacks in open dishes and 100% of termite workers and soldiers died, even though the soldiers were significantly more aggressive towards the ants. The results of predation experiments where larger ant and termite colony fragments interacted provide experimental evidence for the importance of physical barriers for termite colony defense. In experiments where the termites nested within artificial nests (sand-filled containers), A. rudis was aggressive at invading termite nests and inflicted 100% mortality on the termites. In contrast, termite mortality was comparable to controls when termite colonies nested in natural nests comprised of wood blocks. Our results highlight the importance of physical barriers in termite colony defense and suggest that under natural field conditions termites may be less susceptible to attacks by ants when they nest in solid wood, which may offer more structural protection than sand alone.     

Sand Pile Formation in <Emphasis Type="Italic">Dorymyrmex</Emphasis> Ants

We studied circular sand pile formation by two colonies of Brazilian Dorymyrmex ants, in which workers dumped sand excavated from their underground nest around the nest entrance hole. In most cases a worker dumped its load just beyond the ridge of the pile. Each dumped piece either stayed where it was deposited (81.9% in colony A and 73.0% in colony B) or rolled down the outer slope of the sand pile away from the entrance (17.9% in colony A and 27.0% in colony B). Ants almost never dumped in a way that resulted in the load rolling back to the entrance. When one side of the sand pile was experimentally removed, ants preferentially dumped soil on the now flat side, thereby restoring the original circular shape.     

Colony defence against ants inVespa

Summary On Ishigaki Island in southern Japan, despite the prevalence of ants in the study area, none of the failures of 54Vespa affinis (L.) colonies located could be directly attributed to attacks from ants. The long vestibule of theV. affinis embryo nest was not effective in preventing access to the nest by small species of ants.V. affinis andV. tropica (L.) females produce a substance which is repellent to ants. The substance is produced by the 6th and 7th abdominal sternal glands and is thought to be applied to the embryo nest petiole via the sternal brush. As the substance is produced by workers and queens during the entire life of the colony, it probably has a dual function.