Communication in the migratory termite-hunting ant Pachycondyla (= Termitopone) marginata (Formicidae, Ponerinae)

The Neotropical species Pachycondyla marginata conducts well-organized predatory raids on the termite species Neocapritermes opacus and frequently emigrates to new nest sites. During both activities the ants employ chemical trail communication. The trail pheromone orginates from the pygidial gland. Among the substances identified in the pygidial gland secretions, only citronellal was effective as a trail pheromone. Isopulegol elicited an increase in locomotory activity in the ants and may function as a synergist recruitment signal. The chemical signal is enhanced by a shaking display performed by the recruiting ant.     

Cleptobiosis in the antEctatomma ruidum in Nicaragua

Summary Observations of the ponerine antEctatomma ruidum suggested that this is a cleptobiotic species which appears to use the pheromone trails of other ant species to locate individual workers carrying food. To test this hypothesis an arena was set up to quantify the position of eachE. ruidum that entered the arena with respect to its position on or off a well-established foraging trail ofPheidole radoszkowskii, a myrmicine. Encounters betweenE. ruidum andP. radoszkowskii are described. Quantitative data and behavioral observations support the cleptobiosis hypothesis. This study adds yet another dimension to the diverse array of foraging strategies of the Ponerinae.     

Effect of gland extracts on digging and residing preferences of red imported fire ant workers (Hymenoptera: Formicidae)

There is evidence that ant‐derived chemical stimuli are involved in regulating the digging behavior in Solenopsis invicta Buren. However, the source gland(s) and chemistry of such stimuli have never been revealed. In this study, extracts of mandibular, Dufour's, postpharyngeal, and poison glands were evaluated for their effect on ant digging and residing preferences of S. invicta workers from three colonies. In the intracolonial bioassays, workers showed significant digging preferences to mandibular gland extracts in 2 of 3 colonies and significant residing preferences in 1 of 3 colonies; significant digging preferences to Dufour's gland extracts in 1 of 3 colonies and significant residing preferences in 2 of 3 colonies. No digging and residing preferences were found for postpharyngeal and poison gland extracts. In intercolonial bioassays, significant digging and residing preferences were found for mandibular gland extracts in 3 of 6 colony combinations. Significant digging preferences to Dufour's gland extracts were found in 4 of 6 colony combinations and significant residing preferences in all 6 colony combinations. For postpharyngeal gland extracts, significant digging preferences were found only in 1 of 6 colonial combinations and no significant residing preferences were found. For poison gland extracts, no significant digging preferences were found; significant residing preferences were found in 1 of 6 colony combinations. However, a significant residing deterrence (negative residing preference index) was found for 2 of 6 colony combinations. Statistical analyses using data pooled from all colonies showed that mandibular and Dufour's gland extracts caused significant digging and residing preferences in both intracolonial and intercolonial bioassays but not postpharyngeal and poison gland extracts. By analyzing the data pooled from the same three colonies used for gland extract bioassays, it was found that, in no cases, workers showed significant digging and residing preferences to 2‐ethyl‐3,6‐dimethylpyrazine, an alarm pheromone component from mandibular gland.     

Chemical Profiles of Two Pheromone Glands Are Differentially Regulated by Distinct Mating Factors in Honey Bee Queens (Apis mellifera L.)

Pheromones mediate social interactions among individuals in a wide variety of species, from yeast to mammals. In social insects such as honey bees, pheromone communication systems can be extraordinarily complex and serve to coordinate behaviors among many individuals. One of the primary mediators of social behavior and organization in honey bee colonies is queen pheromone, which is produced by multiple glands. The types and quantities of chemicals produced differ significantly between virgin and mated queens, and recent studies have suggested that, in newly mated queens, insemination volume or quantity can affect pheromone production. Here, we examine the long-term impact of different factors involved during queen insemination on the chemical composition of the mandibular and Dufour''s glands, two of the major sources of queen pheromone. Our results demonstrate that carbon dioxide (an anesthetic used in instrumental insemination), physical manipulation of genital tract (presumably mimicking the act of copulation), insemination substance (saline vs. semen), and insemination volume (1 vs. 8 µl) all have long-term effects on mandibular gland chemical profiles. In contrast, Dufour''s gland chemical profiles were changed only upon insemination and were not influenced by exposure to carbon dioxide, manipulation, insemination substance or volume. These results suggest that the chemical contents of these two glands are regulated by different neuro-physiological mechanisms. Furthermore, workers responded differently to the different mandibular gland extracts in a choice assay. Although these studies must be validated in naturally mated queens of varying mating quality, our results suggest that while the chemical composition of Dufour''s gland is associated with mating status, that of the mandibular glands is associated with both mating status and insemination success. Thus, the queen appears to be signaling both status and reproductive quality to the workers, which may impact worker behavior and physiology as well as social organization and productivity of the colony.     

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.     

Communication in the primitive cryptobiotic ant Prionopelta amabilis (Hymenoptera: Formicidae)

Summary The Neotropical ant Prionopelta amabilis, a cryptobiotic species in the phylogenetically primitive tribe Amblyoponini, lives in subterranean habitats, where it preys preferentially on campodeid diplurans and other small arthropods. Here we report that the species employs chemical recruitment and orientation trails during foraging and nest emigrations. The trail pheromone originates in a hitherto unknown basitarsal gland located in the basitarsus of the hindlegs. Trails are laid by a special foot dragging behavior. During the recruitment process the chemical trail signal is complemented by body shaking on the part of the recruiting ant. Foragers frequently wipe the basitarsal gland opening in the hindlegs with the grooming apparatus of the front legs. This latter structure is equipped with unusual glands evidently specialized for this purpose.     

A sophisticated,modular communication contributes to ecological dominance in the invasive ant <Emphasis Type="Italic">Anoplolepis gracilipes</Emphasis>

The ecological success of ants is founded on cooperative behaviour and a well functioning communication. Particularly invasive ants are able to act highly cooperatively, out-compete other species, and become ecologically dominant. Since ant communication is to a large extent chemical, we investigated the pheromone functions involved in foraging and alarm behaviour of the invasive tropical formicine Anoplolepis gracilipes. Our results suggest that long-lasting orientation cues are located in hindguts, while Dufour glands contain short-term attractants that trigger an effective recruitment. Poison gland effects were intermediate between hindgut and Dufour gland in terms of orientation, attraction and longevity. In contrast to the other pheromone sources, mandibular glands have a repellent effect and are most likely involved in alarm behaviour. Taken together, the pheromone glands of A. gracilipes contain functionally distinct signals with considerable differences in persistence. In this respect, its communication is exceptional in formicine ants. A strikingly similar communication system was previously detected in Paratrechina longicornis, another opportunistic and invasive formicine ant. Based on these similarities and the differences compared to non-invasive formicine ants, we discuss the role of chemical signals for the coordination of efficient foraging. We conclude that a sophisticated communication system can contribute significantly to ecological dominance and invasive success, in concert with other well known traits.     

Road to Royalty – Transition of Potential Queen to Queen in the Primitively Eusocial Wasp Ropalidia marginata

Ropalidia marginata, a primitively eusocial wasp, is different from typical primitively eusocial species in having docile queens who cannot be using dominance to maintain reproductive monopoly and instead appear to use a pheromone from the Dufour's gland to do so. When a docile queen is removed from her colony, one of the workers (potential queen, PQ) becomes highly aggressive, and if the queen is not returned, gradually loses her aggression and becomes the new docile queen within a few days. We hypothesized that the decrease in aggression of the PQ with time since queen removal should be correlated with her change in ovaries and pheromone profile. Because the Dufour's gland hydrocarbon composition in R. marginata can be correlated with fertility, this also gave us an opportunity to test whether PQ is different from workers in her Dufour's gland hydrocarbons. In this study, we therefore trace the road to royalty in R. marginata, that is, the transition of the PQ during queen establishment, in terms of her ovaries, aggression, and Dufour's gland hydrocarbons. Our study focuses on queen establishment, which is important for understanding how reproductive conflict can be manifested and resolved.     

Sting,Carry and Stock: How Corpse Availability Can Regulate De-Centralized Task Allocation in a Ponerine Ant Colony

We develop a model to produce plausible patterns of task partitioning in the ponerine ant Ectatomma ruidum based on the availability of living prey and prey corpses. The model is based on the organizational capabilities of a “common stomach” through which the colony utilizes the availability of a natural (food) substance as a major communication channel to regulate the income and expenditure of the very same substance. This communication channel has also a central role in regulating task partitioning of collective hunting behavior in a supply&demand-driven manner. Our model shows that task partitioning of the collective hunting behavior in E. ruidum can be explained by regulation due to a common stomach system. The saturation of the common stomach provides accessible information to individual ants so that they can adjust their hunting behavior accordingly by engaging in or by abandoning from stinging or transporting tasks. The common stomach is able to establish and to keep stabilized an effective mix of workforce to exploit the prey population and to transport food into the nest. This system is also able to react to external perturbations in a de-centralized homeostatic way, such as to changes in the prey density or to accumulation of food in the nest. In case of stable conditions the system develops towards an equilibrium concerning colony size and prey density. Our model shows that organization of work through a common stomach system can allow Ectatomma ruidum to collectively forage for food in a robust, reactive and reliable way. The model is compared to previously published models that followed a different modeling approach. Based on our model analysis we also suggest a series of experiments for which our model gives plausible predictions. These predictions are used to formulate a set of testable hypotheses that should be investigated empirically in future experimentation.     

Chemical interference competition by Monomorium minimum (Hymenoptera: Formicidae)

Summary Workers of Monomorium minimum forage above-ground for dead arthropods. Small particles (<1 mg) are retrieved individually, but larger particles stimulate recruitment and are dissected by groups of workers. The recruitment pheromone originates in the Dufour's gland and the number of ants responding to a trail varies with pheromone concentration. When ants of other species are encountered at food resources, workers of M. minimum gaster-flag and extrude an irritating poison gland secretion from the sting. This chemical interference delays invasion by competitors and prolongs the period during which the colony can dissect and retrieve pieces of the food resource. M. minimum recruits at higher temperatures than sympatric ant species. The probability of interference at food baits rises from 5% to 100% when they become too large for a single worker to carry. The probability of food resource loss is higher for baits of intermediate weight (x=18.1 mg) than for those of low weight (x=0.1 mg) or high weight (x=403.1 mg).     

Ant Trail Pheromone Biosynthesis Is Triggered by a Neuropeptide Hormone

Our understanding of insect chemical communication including pheromone identification, synthesis, and their role in behavior has advanced tremendously over the last half-century. However, endocrine regulation of pheromone biosynthesis has progressed slowly due to the complexity of direct and/or indirect hormonal activation of the biosynthetic cascades resulting in insect pheromones. Over 20 years ago, a neurohormone, pheromone biosynthesis activating neuropeptide (PBAN) was identified that stimulated sex pheromone biosynthesis in a lepidopteran moth. Since then, the physiological role, target site, and signal transduction of PBAN has become well understood for sex pheromone biosynthesis in moths. Despite that PBAN-like peptides (∼200) have been identified from various insect Orders, their role in pheromone regulation had not expanded to the other insect groups except for Lepidoptera. Here, we report that trail pheromone biosynthesis in the Dufour''s gland (DG) of the fire ant, Solenopsis invicta, is regulated by PBAN. RNAi knock down of PBAN gene (in subesophageal ganglia) or PBAN receptor gene (in DG) expression inhibited trail pheromone biosynthesis. Reduced trail pheromone was documented analytically and through a behavioral bioassay. Extension of PBAN''s role in pheromone biosynthesis to a new target insect, mode of action, and behavioral function will renew research efforts on the involvement of PBAN in pheromone biosynthesis in Insecta.     

Food collection and response to pheromones in an ant species exposed to electromagnetic radiation

We used the ant species Myrmica sabuleti as a model to study the impact of electromagnetic waves on social insects' response to their pheromones and their food collection. We quantified M. sabuleti workers' response to their trail, area marking and alarm pheromone under normal conditions. Then, we quantified the same responses while under the influence of electromagnetic waves. Under such an influence, ants followed trails for only short distances, no longer arrived at marked areas and no longer orientated themselves to a source of alarm pheromone. Also when exposed to electromagnetic waves, ants became unable to return to their nest and recruit congeners; therefore, the number of ants collecting food increases only slightly and slowly. After 180 h of exposure, their colonies deteriorated. Electromagnetic radiation obviously affects social insects' behavior and physiology.     

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.     

Recruitment in starved nests: the role of direct and indirect interactions between scouts and nestmates in the ant <Emphasis Type="Italic">Lasius niger</Emphasis>

In social insects, the foraging activity usually increases with the length of food deprivation. In Lasius niger, a mass-recruiting ant species, the foraging adjustment to the level of food deprivation is regulated by the scout that fed at the food source and by the response of the nestmates to signals performed by the scout inside the nest. In this study, we look at the role of these direct interactions (antennations or trophallaxes) and indirect interactions (pheromonal emission) and how they are influenced by the level of food deprivation. At the beginning of recruitment, the relative number of nestmates leaving the nest to forage increases with the level of deprivation. The nestmates’ propensity to exit the nest is not influenced by a previous trophallactic and/or antennal contact with a scout. Our results strongly suggest that the exit of nestmates is triggered by a chemical signal emitted by a scout. Deprivation lowers the response threshold of nestmates to this chemical signal resulting in a more important exit from the nest. Surprisingly, 27% of starved nestmates that receive food from the scout relay the information by depositing a chemical signal before having discovered and drunk the food source. Both phenomena boost the recruitment process. Though successful foragers returning to the nest have a significant role in the recruitment to the food source, we observed that the response of the nestmates inside the nest also greatly influence regulation of the foraging activity.     

Predatory behavior of a seed-eating ant:Brachyponera senaarensis

The great flexibility of the feeding strategies exhibited by the ponerine ant Brachyponera senaarensis (Mayr) allows it to exploit either seeds or animal prey items as food resources. Predation is generally limited to small prey and is very similar to scavenging behavior. In laboratory conditions, the predatory behavior of B. senaarensis is not different in structure from that known in other carnivorous ants species. The workers forage individually and return to the nest using a series of cues involving light, a chemical graduated marking system near the nest entrance, and memory. During nest-moving, recruitment by tandem running was observed. However, in colonies where the food supply is regular, workers that discover food do not recruit nestmates, but make repeated trips between the nest and the food source. On the contrary, in starved colonies, the introduction of prey may produce a massive exit of foragers, corresponding to a primitive form of mass recruitment similar to that observed in some other ant species.     

Optimality of collective choices: a stochastic approach

Amplifying communication is a characteristic of group-living animals. This study is concerned with food recruitment by chemical means, known to be associated with foraging in most ant colonies but also with defence or nest moving. A stochastic approach of collective choices made by ants faced with different sources is developed to account for the fluctuations inherent to the recruitment process. It has been established that ants are able to optimize their foraging by selecting the most rewarding source. Our results not only confirm that selection is the result of a trail modulation according to food quality but also show the existence of an optimal quantity of laid pheromone for which the selection of a source is at the maximum, whatever the difference between the two sources might be. In terms of colony size, large colonies more easily focus their activity on one source. Moreover, the selection of the rich source is more efficient if many individuals lay small quantities of pheromone, instead of a small group of individuals laying a higher trail amount. These properties due to the stochasticity of the recruitment process can be extended to other social phenomena in which competition between different sources of information occurs.     

Impact of natural parasitism by two eucharitid wasps on a potential biocontrol agent ant in southeastern Mexico

Eucharitids are specialized parasitoids of ants. The biology, life cycle and chemical ecology are known for a number of species, but the study of the impact of eucharitid wasps upon their ant hosts has been seldom addressed. Here, we determine the prevalence of the parasitism of two sympatric Kapala species upon a population of the neotropical ant Ectatomma ruidum, along a 12-month sampling period. Adult and immature parasitoids were present in the nests all year round, and several cases of superparasitism were observed. Parasitism varied strongly among the nests for any collecting date and among collecting dates, but the prevalence of Kapala parasitoids increased significantly during the rainy season, and the probability for a nest of being parasitized was positively correlated with colony size, particularly with cocoon number. At the population scale, more than 28% of all E. ruidum pupae produced during the ant reproductive and dispersal period (June) were infested. Our results are discussed from the point of view of the impact of these parasitoids on the colonies of E. ruidum, a potential biocontrol agent in coffee and cocoa plantations in southeastern Mexico.     

Intraspecific Food‐Robbing and Neighborhood Competition: Consequences for Anti‐Robber Vigilance and Colony Productivity

Most social animals have mechanisms to distinguish group members from outsiders, in part to prevent the exploitation of resources reserved for members of the group. Nevertheless, specialized thieves of the Neotropical ant, Ectatomma ruidum, also known as the ‘thieving ant’, regularly enter and steal resources from distinct, neighboring colonies. Here, we examine the mechanisms and consequences of thievery in a population of E. ruidum. We show that (1) individuals from nearby colonies were accepted more often than those from farther colonies; (2) rejection rates decreased as individuals interacted more with non‐nestmates from the same source colony; and (3) colonies that were experimentally treated to reduce thievery rates had improved productivity. The boost in productivity with thievery reduction was greater in low density populations than in high density populations. We conclude that, as in other species, thievery has negative fitness costs to E. ruidum. However, greater acceptance of neighbors than non‐neighbors and increased acceptance after habituation to non‐nestmates suggest a proximate explanation for the presence of thievery. Moreover, lower fitness costs of thievery at high nesting density, combined with observations of extraordinarily high densities of E. ruidum throughout its range, suggest there is little selection pressure among these ants to guard against thieves, thus providing an ultimate explanation why thievery persists among litter‐foraging ants.     

The orientation inducer pheromone of the fire ant Solenopsis invicta

Abstract Foraging ants recruit nestmate workers to food sources by a variety of mechanisms. We report that one behavioural subcategory of the recruitment pheromone complex of Solenopsis invicta Buren involves orientation induction. The orientation inducer pheromone exerts its effects by changing the physiological state of the recipient rather than by releasing a measurable behaviour. Some ant species use a physical 'waggle' behaviour to motivate (change physiological state) nestmate workers to follow their chemical trail. The orientation inducer pheromone can be interpreted as a chemical analogue of the physical 'waggle' inducing effects. This behaviour is not elicited by the recruitment pheromone components responsible for orientation and/or attraction. Each of these behavioural categories is mediated by a different blend of chemicals from the Dufour's gland. Activity-concentration thresholds indicate that the attraction and inducer part of the recruitment pheromone require about 250 times more worker equivalents for a response than the orientation pheromone. Therefore, the recruitment sub-categories are differentially activated by the amount of Dufour's gland material released.     

Alarm communication in <Emphasis Type="Italic">Ropalidia</Emphasis> social wasps

Summary Alarm pheromones, chemical substances produced by social insects to alert the colony to threat, are the principal means by which colony defence is co-ordinated. We present the results of a study on alarm behaviour in 5 swarming species of wasps belonging to the genus Ropalidia. These species show a remarkably efficient strategy of alarm communication, including visual display and attack synchronization. We show that pheromones released from the venom gland play an important role in alarm recruitment in species belonging to the Ropalidia flavopicta group, but not in Ropalidia sumatrae. We analysed the contents of the venom reservoirs content of four of the studied species by gas chromatography-mass spectrometry. Glands were found to contain a complex mixture of volatile compounds as well as spiroacetals of higher molecular weight. Interestingly, despite all species producing similar chemical compounds from the venom gland, these were found to elicit alarm behaviour in only those species that build nest envelopes, suggesting a link between chemical release of alarm behaviour and the evolution of nest architecture in Ropalidia wasps.Received 19 August 2003; revised 29 February 2004; accepted 10 March 2004