Trail Pheromone of the Argentine Ant,Linepithema humile (Mayr) (Hymenoptera: Formicidae)

The Argentine ant (Linepithema humile) is recognized as one of the world''s most damaging invasive species. One reason for the ecological dominance of introduced Argentine ant populations is their ability to dominate food and habitat resources through the rapid mobilization and recruitment of thousands of workers. More than 30 years ago, studies showed that (Z)-9-hexadecenal strongly attracted Argentine ant workers in a multi-choice olfactometer, suggesting that (Z)-9-hexadecenal might be the trail pheromone, or a component of a trail pheromone mixture. Since then, numerous studies have considered (Z)-9-hexadecenal as the key component of the Argentine ant trails. Here, we report the first chemical analyses of the trails laid by living Argentine ants and find that (Z)-9-hexadecenal is not present in a detectible quantity. Instead, two iridoids, dolichodial and iridomyrmecin, appear to be the primary chemical constituents of the trails. Laboratory choice tests confirmed that Argentine ants were attracted to artificial trails comprised of these two chemicals significantly more often than control trails. Although (Z)-9-hexadecenal was not detected in natural trails, supplementation of artificial dolichodial+iridomyrmecin trails with an extremely low concentraion of (Z)-9-hexadecenal did increase the efficacy of the trail-following behavior. In stark contrast with previous dogma, our study suggests that dolichodial and iridomyrmecin are major components of the Argentine ant trail pheromone. (Z)-9-hexadecenal may act in an additive manner with these iridoids, but it does not occur in detectable quantities in Argentine ant recruitment trails.     

The ecology and feeding habits of the arboreal trap-jawed ant Daceton armigerum

Here we show that Daceton armigerum, an arboreal myrmicine ant whose workers are equipped with hypertrophied trap-jaw mandibles, is characterized by a set of unexpected biological traits including colony size, aggressiveness, trophobiosis and hunting behavior. The size of one colony has been evaluated at ca. 952,000 individuals. Intra- and interspecific aggressiveness were tested and an equiprobable null model used to show how D. armigerum colonies react vis-à-vis other arboreal ant species with large colonies; it happens that D. armigerum can share trees with certain of these species. As they hunt by sight, workers occupy their hunting areas only during the daytime, but stay on chemical trails between nests at night so that the center of their home range is occupied 24 hours a day. Workers tend different Hemiptera taxa (i.e., Coccidae, Pseudococcidae, Membracidae and Aethalionidae). Through group-hunting, short-range recruitment and spread-eagling prey, workers can capture a wide range of prey (up to 94.12 times the mean weight of foraging workers).     

Arboreal Ants Use the “Velcro? Principle” to Capture Very Large Prey

Plant-ants live in a mutualistic association with host plants known as “myrmecophytes” that provide them with a nesting place and sometimes with extra-floral nectar (EFN) and/or food bodies (FBs); the ants can also attend sap-sucking Hemiptera for their honeydew. In return, plant-ants, like most other arboreal ants, protect their host plants from defoliators. To satisfy their nitrogen requirements, however, some have optimized their ability to capture prey in the restricted environment represented by the crowns of trees by using elaborate hunting techniques. In this study, we investigated the predatory behavior of the ant Azteca andreae which is associated with the myrmecophyte Cecropia obtusa. We noted that up to 8350 ant workers per tree hide side-by-side beneath the leaf margins of their host plant with their mandibles open, waiting for insects to alight. The latter are immediately seized by their extremities, and then spread-eagled; nestmates are recruited to help stretch, carve up and transport prey. This group ambush hunting technique is particularly effective when the underside of the leaves is downy, as is the case for C. obtusa. In this case, the hook-shaped claws of the A. andreae workers and the velvet-like structure of the underside of the leaves combine to act like natural Velcro® that is reinforced by the group ambush strategy of the workers, allowing them to capture prey of up to 13,350 times the mean weight of a single worker.     

An uneasy alliance:a nesting association between aggressive ants and equally fierce social wasps

Although the Neotropical territorially dominant arboreal ant Azteca chartifex Forel is very aggressive towards any intruder,its populous colonies tolerate the close presence of the fierce polistine wasp Polybia rejecta(F.).In French Guiana,83.33%of the 48 P.rejecta nests recorded were found side by side with those of A.chartifex.This nesting association results in mutual protection from predators(i.e.,the wasps protected from army ants;the ants protected from birds).We conducted field studies,laboratorybased behavioral experiments and chemical analyses to elucidate the mechanisms allowing the persistence of this association.Due to differences in the cuticular profiles of the two species,we eliminated the possibility of chemical mimicry.Also,analyses of the carton nests did not reveal traces of marking on the envelopes.Because ant forager flows were not perturbed by extracts from the wasps’Dufour’s and venom glands,we rejected any hypothetical action of repulsive chemicals.Nevertheless,we noted that the wasps"scraped"the surface of the upper part of their nest envelope using their mandibles,likely removing the ants'scent trails,and an experiment showed that ant foragers were perturbed by the removal of their scent trails.This leads us to use the term"erasure hypothesis."Thus,this nesting association persists thanks to a relative tolerance by the ants towards wasp presence and the behavior of the wasps that allows them to"contain"their associated ants through the elimination of their scent trails,direct attacks,"wing-buzzing"behavior and ejecting the ants.     

Host-ant trail following by myrmecophilous larvae of Liphyrinae (Lepidoptera,Lycaenidae)

In this study we report a case of ant-trail following by lycaenid caterpillars. Euliphyra mirifica and E. leucyana caterpillars are involved in a commensal association with the weaver ant Oecophylla longinoda. The host nests are made with leaves which over the course of time dry out or are broken open by storms, forcing the ants to migrate and build a new nest elsewhere. Euliphyra caterpillars are stimulated by recruitment behaviour which triggers the migration of their host. They then follow the host trails leading to the new nesting site. Laboratory experiments showed that these caterpillars are able to follow host trails under varied conditions: (1) fresh trails actually used by workers, (2) fresh trails in the absence of workers, (3) heterocolonial, 2-month-old trails, and (4) fresh trails washed with water (to simulate the effect of tropical rains). They can also bridge trail gaps of more than 1 cm. Under natural conditions, the trails are frequently situated along thin twigs. The forward progress of the ants in such a situation is not impeded by the presence of large Euliphyra larvae. Workers just climb over the caterpillars, even on larger trails where there is enough room to pass alongside them. This suggests that an allomone is secreted on the dorsal part of the caterpillars. When crawling along heterocolonial trails, the caterpillars are not attacked, even if about 21% of the workers from the new colony spread their mandibles when encountering them. They are then adopted and are admitted to the nest of the new host colony of O. longinoda.     

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.     

Chemical communication during foraging in the harvesting ants Messor pergandei and Messor andrei

We combined behavioral analyses in the laboratory and field to investigate chemical communication in the formation of foraging columns in two Nearctic seed harvesting ants, Messor pergandei and Messor andrei. We demonstrate that both species use poison gland secretions to lay recruitment trails. In M. pergandei, the recruitment effect of the poison gland is enhanced by adding pygidial gland secretions. The poison glands of both species contain 1-phenyl ethanol. Minute quantities (3 μl of a 0.1 ppm solution) of 1-phenyl ethanol drawn out along a 40 cm long trail released trail following behavior in M. pergandei, while M. andrei required higher concentrations (0.5–1 ppm). Messor pergandei workers showed weak trail following to 5 ppm trails of the pyrazines 2,5-dimethylpyrazine and 2,3,5-trimethylpyrazine, whereas M. andrei workers showed no behavioral response. Minute quantities of pyrazines were detected in M. pergandei but not in M. andrei poison glands using single ion monitoring gas chromatography–mass spectrometry.     

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.     

Stingless bees (<Emphasis Type="Italic">Scaptotrigona pectoralis</Emphasis>) learn foreign trail pheromones and use them to find food

Foragers of several species of stingless bees (Hymenoptera, Apidae and Meliponini) deposit pheromone marks in the vegetation to guide nestmates to new food sources. These pheromones are produced in the labial glands and are nest and species specific. Thus, an important question is how recruited foragers recognize their nestmates’ pheromone in the field. We tested whether naïve workers learn a specific trail pheromone composition while being recruited by nestmates inside the hive in the species Scaptotrigona pectoralis. We installed artificial scent trails branching off from trails deposited by recruiting foragers and registered whether newly recruited bees follow these trails. The artificial trails were baited with trail pheromones of workers collected from foreign S. pectoralis colonies. When the same foreign trail pheromone was presented inside the experimental hives while recruitment took place a significant higher number of bees followed the artificial trails than in experiments without intranidal presentation. Our results demonstrate that recruits of S. pectoralis can learn the composition of specific trail pheromone bouquets inside the nest and subsequently follow this pheromone in the field. We, therefore, suggest that trail pheromone recognition in S. pectoralis is based on a flexible learning process rather than being a genetically fixed behaviour.     

Interspecific Trail Following and Commensalism Between the Ponerine Ant Gnamptogenys menadensis and the Formicine Ant Polyrhachis rufipes

Gnamptogenys menadensis (subfamily Ponerinae) foragers use chemical trails to home to their nests. Although prey capture and retrieval are generally performed solitarily, trails seem to enhance foraging to areas rich in prey or to sugar sources. Trail laying and following are most conspicuous during nest migration. These trails are laid down by tapping the sting onto the substrate. In laboratory tests, only extracts from the Dufour's gland were readily followed. Workers of Polyrhachis rufipes (Formicinae) use the trails of G. menadensis to gain access to otherwise nonavailable sugar sources. When they encounter Gnamptogenys foragers, P. rufipes workers show a typical aggressive antennal boxing, to which Gnamptogenys reacts with a submissive behavior. This is the first report of commensalism between a ponerine and a formicine ant.     

Trail Communication During Foraging and Recruitment in the Subterranean Termite Reticulitermes santonensis De Feytaud (Isoptera, Rhinotermitidae)

The search for food in the French subterranean termite Reticulitermes santonensis De Feytaud is organized in part by chemical trails laid with the secretion of their abdominal sternal gland. Trail-laying and -following behavior of R. santonensis was investigated in bioassays. During foraging for food termites walk slowly (on average, 2.3 mm/s) and lay a dotted trail by dabbing the abdomen at intervals on the ground. When food is discovered they return at a quick pace (on average, 8.9 mm/s) to the nest, laying a trail for recruiting nestmates to the food source. While laying this recruitment trail the workers drag the abdomen continuously on the ground. The recruitment trail is highly attractive: it is followed within a few seconds, by more nestmates, and at a quicker pace (on average, 6.4 mm/s) than foraging trails (on average, 2.9 mm/s). The difference between foraging and recruitment trails in R. santonensis could be attributed to different quantities of trail pheromone. A caste-specific difference in trail pheromone thresholds, with workers of R. santonensis being more sensitive to trails than soldiers, was also documented: soldiers respond only to trails with a high concentration of trail pheromone.     

Mandible-Powered Escape Jumps in Trap-Jaw Ants Increase Survival Rates during Predator-Prey Encounters

Animals use a variety of escape mechanisms to increase the probability of surviving predatory attacks. Antipredator defenses can be elaborate, making their evolutionary origin unclear. Trap-jaw ants are known for their rapid and powerful predatory mandible strikes, and some species have been observed to direct those strikes at the substrate, thereby launching themselves into the air away from a potential threat. This potential escape mechanism has never been examined in a natural context. We studied the use of mandible-powered jumping in Odontomachus brunneus during their interactions with a common ant predator: pit-building antlions. We observed that while trap-jaw ant workers escaped from antlion pits by running in about half of interactions, in 15% of interactions they escaped by mandible-powered jumping. To test whether escape jumps improved individual survival, we experimentally prevented workers from jumping and measured their escape rate. Workers with unrestrained mandibles escaped from antlion pits significantly more frequently than workers with restrained mandibles. Our results indicate that some trap-jaw ant species can use mandible-powered jumps to escape from common predators. These results also provide a charismatic example of evolutionary co-option, where a trait that evolved for one function (predation) has been co-opted for another (defense).     

Exocrine glands of the ant Myrmoteras iriodum

This paper describes the morphological characteristics of nine major exocrine glands in workers of the formicine ant Myrmoteras iriodum. The elongate mandibles reveal along their entire length a conspicuous intramandibular gland, which contains both class‐1 and class‐3 secretory cells. The secretory cells of the mandibular glands show a peculiar appearance, with a branched end apparatus, which is unusual for ants. The other major glands (pro‐ and postpharyngeal gland, infrabuccal cavity gland, labial gland, metapleural gland, venom gland and Dufour gland) show common features for formicine ants. The precise function of the glands could not yet be experimentally demonstrated, and to clarify this will depend on the availability of live material of these enigmatic ants in future.     

The dynamics of collective exploration and trail-formation in Monomorium pharaonis: experiments and model

Abstract. When exploring a chemically unmarked area devoid of food sources, workers of the pest ant Monomorium pharaonis L. (Formicidae, Myrmicinae) leave scent marks on the ground and after 30–60min a network of diverging exploratory trails begins to emerge.
Exploratory activity is affected by the nutritional state of the colony and a period of food deprivation induces a dramatic increase in the number of workers leaving the nest. A mathematical model based on a logistic growth equation is proposed to describe the exploratory recruitment observed. When travelling along exploratory trails the proportion of ants displaying trail-laying behaviour is higher for outbound than for nestbound workers. Outbound ants also show a greater propensity than nestbound ants to follow the scent marks of their nestmates. The chemical used to mark a novel area does not appear to be colony-specific and thus does not have a territorial function sensu stricto. The adaptive value of the collective exploratory behaviour observed in this study is discussed in relation to the common features of other pest ant species described in the literature.     

Initial behavior in colony fragments of an introduced population of the invasive ant Wasmannia auropunctata

We investigated in the laboratory the initial behavior of propagules of the invasive ant Wasmannia auropunctata in Cameroon where it has been introduced. Both workers and queens at first feigned death (thanatosis), and then the workers slowly moved around the experimental arena; the queens did the same about 10seconds later. Each queen antennated selected workers that then aggregated together by grasping the hind leg of another ant with their mandibles. When encountering the queen again, the lead worker climbed up the queen's hind leg and onto her back, followed by some other individuals. The remaining workers followed the queen to a location in the experimental arena. When brood was present, the workers transferred it to this location. Orphaned workers did not aggregate, but gathered the brood together and took care of it. By permitting propagules to survive, these behaviors likely contribute to the success of W.?auropunctata as an invader.     

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.     

Leaf density and a trade-off between load-size selection and recruitment behavior in the ant Atta cephalotes

This study considers the interplay between individual load-size selection and recruitment behavior in the leaf-cutting ant Atta cephalotes. Foraging workers anchor themselves on the leaf edge by their hind legs and pivot around them while cutting arcs from leaves. Since workers not only cut leaves but also lay chemical trails to recruit nestmates, we investigated whether there is conflict of motivation affecting the workers' decision either to quickly inform nestmates about a newly discovered food source, or instead to cut full-load leaf fragments, which could delay recruitment. Workers were presented with leaves of privet of three different grades of toughness (measured as leaf density=mass/area) as sources of different quality, and load-size selection and recruitment behavior by harvesting-satiated and harvesting-deprived workers were measured. The following results were obtained. (1) Leaf density affected individual load-size selection: both harvesting-satiated and harvesting-deprived workers were found to cut smaller leaf fragments from the denser leaves. (2) Harvesting-deprived workers cut smaller fragments than harvesting-satiated workers, and therefore saved cutting time. The fragments cut were smaller only during the initial phases of the recruitment process, when information about the discovery needed to be transferred. (3) Harvesting-deprived workers showed higher recruitment rates than harvesting-satiated workers. A considerable number of ants were observed to return to the nest unladen. During the initial phases, the ratio of laden/unladen workers was lower than that for harvesting-satiated workers, and increased with the development of the tograging process. (4) Scout workers confronted with familiar leaves ran back to the nest laying chemical trails without even contacting the leaves. They relied on olfactory cues to start recruiting nestmates, and leaf density played no role in their decisions. (5) When confronted with unfamiliar leaves, on the other hand, they assessed leaf quality by probing bites at the leaf edge, although no actual cuts occurred. In this situation, the resulting recruitment rates depended on physical leaf traits, being higher for the tenderer leaves. (6) Workers foraging on unfamiliar leaves cut smaller fragments than workers cutting familiar leaves, and most of them displayed trail-laying behavior when returning to the nest. The results support the hypothesis of a trade-off between time spent collecting and that invested to recruit nestmates. During the initial phases of exploitation of a newly discovered food source, workers reduced their individual carrying performance in order to return earlier to the colony for further recruitment.     

Recruitment and Other Communication Behavior in the Ponerine Ant Ectatomma ruidum

The ponerine ant Ectatomma ruidum, though previously reported to possess only rudimentary recruitment ability, was found to lay chemical trails for mass recruitment to rich or difficult food sources. The pheromone originates from the Dufour's gland, a new source of trail pheromones in the primitive ant subfamily Ponerinae. During nest emigrations, E. ruidum practices stereotyped social carrying in the myrmicine mode. The discovery of this form of social carrying and of a recruitment pheromone in the Dufour's gland secretions support the hypothesis that the subfamily Myrmicinae is derived from an ectatommine ancestor. Other communication behaviors exhibited by E. ruidum include exchange of liquid food carried between the mandibles, chemical alarm communication, nest entrance marking, and an additional social carrying posture previously unknown in ants.     

Marking of Nest Entrances and Vicinity in Two Related Tetramorium Ant Species (Hymenoptera: Formicidae)

Workers of the related ants Tetramorium impurum and T. caespitum mark the vicinity of their nest entrances in a species-specific manner, as seen by similarities between the behavior of nestmates and that of alien conspecifics (e.g., concerning aggregation, locomotion, orientation, tendency to move, and agonistic behavior). Additionally, they mark the inside of their nest entrances in a colony-specific manner, as seen by the following differences in behavior. Nestmates aggregate on these areas, walk rather slowly, but freely and essentially in the middle of the areas, come toward and very near such areas, are not inclined to escape, and are ready to attack possible intruders. Alien conspecifics do not aggregate, walk quickly, and are reluctant to stay on the areas, come neither toward nor very near the areas, are inclined to escape, and often open their mandibles, mainly when in front of a resident. The marking of the nest entrances is performed by T. impurum in 30 min and by T. caespitum in 15 min. If not reinforced, the marking by both species vanishes in 60 and 50 min, respectively. Extracts of hindlegs, metathorax, or metapleural glands produce in unmarked areas the ethological effect of marked entrances. It may be hypothesized that the marking factor is produced by the workers' metapleural glands and deposited onto the ground, via the hindlegs of ants leaving the nest. A worker's head has a species- but not a colony-specific ethological effect. An isolated alien conspecific's head is never attacked, whereas a thorax with abdomen is. This explains why, by opening its mandibles (and then presumably emitting a mandibular gland pheromone), a conspecific ant momentarily inhibits the attack of a nonnestmate. According to Hölldobler and Wilson (1990), the marking of the inside of T. impurum and T. caespitum nest entrances is a territorial and nest-entrance marking, whereas the marking of the close vicinity of the entrances is a home-range marking, as is the marking of the foraging area. These markings are in accordance with the fact that T. impurum foragers deposit their trail pheromone as far as the opening of the nest entrance.     

Courtship with two spoons—Anatomy and presumed function of the bizarre antennae of Cardiocondyla zoserka ant males

Mating in ants often occurs on the wing during nuptial flights or on the ground when scattered female sexuals attract males by pheromones. In both scenarios, there is little opportunity for males to engage in prolonged aggressive competition or elaborate courtship displays. Male morphology is therefore adapted to locating female sexuals and mating, and it lacks specific weapons or other traits associated with courtship. In contrast, sexuals of the ant genus Cardiocondyla typically mate in their natal nests. As a consequence, in many species winged males have been replaced by wingless fighter or territorial males, which kill or expel rival males with their strong mandibles and show complex mating behavior. However, no wingless males are known from Cardiocondyla zoserka from West Africa, and instead, winged males have evolved a bizarre secondary sexual trait: uniquely shaped antennae with spoon‐like tips that show heavily sculptured ventral surfaces with numerous invaginations. We here report on the courtship behavior of C. zoserka males and describe antennal glands with class 3 gland cells, which presumably secrete a close range sex pheromone. Antennal glands have not yet been found in males of other ant species, including a close relative of C. zoserka, suggesting that in ants with intranidal mating sexual selection can rapidly lead to highly divergent adaptations and the evolution of novel structures.