Pygidial gland chemistry and potential alarm-recruitment function in column foraging,but not solitary,Nearctic Messor harvesting ants (Hymenoptera: Formicidae: Myrmicinae)

We investigated the role of the pygidial gland on foraging behavior in two ecologically dominant column foraging Nearctic harvesting ants (Messor pergandei and Messor andrei). Using chemical analyses and behavioral tests, we show that n-tridecane is the major biologically active compound of pygidial gland secretions in both species, and that this chemical functions as a powerful alarm-recruitment pheromone. Another major compound of pygidial gland contents is benzaldehyde; this substance does not release behavioral reactions in M. pergandei workers but might function as a defensive secretion. Six solitary foraging Nearctic Messor and two column foraging Palearctic Messor species, did not have large pygidial gland reservoirs.     

Worker size polymorphism and ethological role of sting associated glands in the harvester ant Messor barbarus

Summary: Though harvester ants are closely similar in ecology, species differ in their worker size polymorphism as well as in the glandular source of their trail pheromones and defensive compounds. In the harvester ant Messor barbarus, we find that the recruitment trail pheromone is located in the Dufour gland, while defence-alarm substances are produced in the poison gland. We also investigated how the glandular development and the ethological response to these abdominal glands are related to worker body size. For both glands, M. barbarus workers show monophasic and nonisometric growths with slopes of allometric regression lines lower than 1. The highest trail-following response is elicited by the Dufour gland secretion from media workers, responsible for most foraging activities in M. barbarus. Aggressive behaviour is more frequently observed in the presence of poison gland secretions from medium and large-sized workers. Differences between species and between worker size classes in the ethological role of sting associated glands are discussed in relation to the foraging ecology and defensive characteristics of harvester ants.     

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.     

Chemical and ethological studies of the trail pheromone of the ant Manica rubida (Hymenoptera: Formicidae)

ABSTRACT. The poison gland of Manica rubida contains nanogram quantities of four alkylpyrazines, methylpyrazine, 2,5-dimethylpyrazine, trimethylpyrazine and 3-ethyl-2,5-dimethylpyrazine, of which only the last induces pronounced trail-following behaviour. Myrmica rubra and M. rubida workers follow each other's trails equally well when allowance is made for the much greater size of M. rubida workers. The cross activity in trail-following between M. rubida, M. rubra and Tetramorium caespitum is understandable in terms of the amounts and proportions of the different pyrazines present in their glands and their responses to the synthetic substances and appropriate mixtures of them.     

Context-dependent navigation in a collectively foraging species of ant, Messor cephalotes

More than 100 years of scientific research has provided evidence for sophisticated navigational mechanisms in social insects. One key role for navigation in ants is the orientation of workers between food sources and the nest. The focus of recent work has been restricted to navigation in individually foraging ant species, yet many species do not forage entirely independently, instead relying on collectively maintained information such as persistent trail networks and/or pheromones. Harvester ants use such networks, but additionally, foragers often search individually for food either side of trails. In the absence of a trail, these ‘off-trail’ foragers must navigate independently to relocate the trail and return to the nest. To investigate the strategies used by ants on and off the main trails, we conducted field experiments with a harvester ant species, Messor cephalotes, by transferring on-trail and off-trail foragers to an experimental arena. We employed custom-built software to track and analyse ant trajectories in the arena and to quantitatively compare behaviour. Our results indicate that foragers navigate using different cues depending on whether they are travelling on or off the main trails. We argue that navigation in collectively foraging ants deserves more attention due to the potential for behavioural flexibility arising from the relative complexity of journeys between food and the nest.     

Recruitment pheromone in the harvester ant genus Pogonomyrmex

Workers of the harvester ant genus Pogonomyrmex employ recruitment trail pheromones discharged from the poison gland. In P. barbatus, P. maricopa, P. occidentalis and P. rugosus we identified three pyrazines [2,5-dimethylpyrazine, trimethylpyrazine and 3-ethyl-2,5-dimethylpyrazine (EDMP)] as major compounds of the volatile part of the poison-gland secretions. Laboratory and field tests revealed EDMP to be the main recruitment pheromone.     

Perceptual differences in trail-following leaf-cutting ants relate to body size

Leaf-cutting ants of the genus Atta have highly size-polymorphic workers, and size is related to division of labor. We studied trail-following behavior of different-sized workers in a laboratory colony of Atta vollenweideri. For small and large workers, we measured responsiveness and preference to artificial conspecific and heterospecific pheromone trails made from poison gland extracts of A. vollenweideri and A. sexdens. Responsiveness was measured as the probability of trail-following, and preference was measured by testing the discrimination between one conspecific and one heterospecific trail. Minute amounts of the releaser component methyl-4-methylpyrrole-2-carboxylate (0.4pg/1m), present in both, conspecific and heterospecific trails, suffice to elicit trail-following behavior. Workers followed heterospecific trails, and these trails (after normalizing their concentration) were as effective as conspecific trails. Small workers were less likely to follow a trail of a given concentration than large workers. In the discrimination test, small workers preferred the conspecific trail over the heterospecific trail, whereas large workers showed no significant preference. It is suggested that large workers primarily respond to the releaser component present in both trails, whereas small workers focus more on the conspecific traits provided by the blend of components contained in the trail pheromone.     

Foraging strategy quick response to temperature of Messor barbarus (Hymenoptera: Formicidae) in Mediterranean environments

Animals principally forage to try to maximize energy intake per unit of feeding time, developing different foraging strategies. Temperature effects on foraging have been observed in diverse ant species; these effects are limited to the duration of foraging or the number of foragers involved. The harvester ant Messor barbarus L. 1767 has a specialized foraging strategy that consists in the formation of worker trails. Because of the high permeability of their body integument, we presume that the length, shape, and type of foraging trails of M. barbarus must be affected by temperature conditions. From mid-June to mid-August 1999, we tested the effect on these trail characteristics in a Mediterranean forest. We found that thermal stress force ants to use a foraging pattern based on the variation of the workers trail structure. Ants exploit earlier well-known sources using long physical trails, but as temperatures increases throughout the morning, foragers reduce the length of the foraging column gradually, looking for alternative food sources in nonphysical trails. This study shows that animal forage can be highly adaptable and versatile in environments with high daily variations.     

Soil texture as an influence on the distribution of the desert seed-harvester ants Pogonomyrmex rugosus and Messor pergandei

Summary Pogonomyrmex rugosus and Messor pergandei are ecologically similar species of desert seed-harvester ants that coexist in numerous areas throughout the Sonoran and Mohave Deserts. However, these two species also commonly segregate along physical gradients, with each species predominating in areas that differ in soil texture and/or topographic relief. Along gradients that included bajada and alluvial flat habitats, P. rugosus occurred alone in coarse-textured soils near mountains, while M. pergandei occurred alone in finer-textured soils further away. Conversely, along a vegetation gradient that included creosote bush and saltbush habitats, P. rugosus occurred alone in finer-textured soils than those occupied by either M. pergandei alone or both species in coexistence. However, in both situations clay content was significantly higher in areas occupied by P. rugosus alone, and at the latter site clay content was correlated with relative abundance of each species. Moreover, local distribution pattern of these two species may be related to the effects of clay on water retention, with retention being highest in areas occupied by P. rugosus alone. Differences in reproductive ecology may also affect these patterns as P. rugosus reproductive flights follow summer monsoon rains, while those of M. pergandei occur during the milder winter and spring.     

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.     

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.     

Fire ant trail pheromones: Analysis of species specificity after gas chromatographic fractionation

The specificity of the trail pheromones of four Solenopsis species was determined using natural trails. Dufour's gland extracts, and purified fractions from Dufour's gland extracts collected after gas-chromatographic separation. S. richteri and S. invicta possess species-specific major trail pheromones, while S. geminata and S. xyloni appear to have a common trail pheromone. Preliminary chemical characterization of the main trail pheromone of S. richteri indicates a M.W. of 218 and empirical formula of C₁₆H₂₆. The trail pheromone system of S. richteri consists of a blend of compounds and this phenomenon may also occur in the other species. The lowest concentration of their trail pheromone that workers of S. richteri could detect was about 10 fg per cm. The significance of blends of pheromones being utilized to generate chemical trails is discussed.     

Contents of the poison apparatus of some species of Pheidole ants

Four Old World species of Pheidole ants contain different mixtures of farnesene-type hydrocarbons in their poison apparatus, and the mixture is different between the minor and major workers within a species. A bishomofarnesene (C₁₇H₂₈) provides approximately half of the secretion of the Dufour glands of minor workers of Pheidole pallidula. (Z,E)-α-Farnesene constituted 96% of the Dufour secretion of major workers of P. pallidula, but only 20% of that of minors. The Dufour glands of minor workers of Pheidole sinaitica contain a mixture of farnesene homologues with (Z,E)-α-farnesene and the bishomofarnesene also found in P. pallidula predominant. The mixture in major workers was similar but had, in addition, a small amount of (E)-β-farnesene. The Dufour glands of Pheidole teneriffana minors contain chiefly the same bishomofarnesene found in P. pallidula and P. sinaitica while major workers contain (Z,E)-α-farnesene. Pheidole megacephala minor workers contained small amounts of eight farnesenes, while major workers contained essentially no farnesenes. The poison glands of minor workers of P. pallidula contain 3-ethyl-2,5-dimethylpyrazine. No pyrazine compounds were found in the major workers of P. pallidula or the minor workers of P. sinaitica. The poison glands of the major workers of P. sinaitica contained larger amounts of tetra-substituted pyrazines. No pyrazines were found in the poison reservoirs of major or minor workers of P. teneriffana or P. megacephala.     

The trail of the african urticating antTetramorium aculeatum: Source,potency, and workers' behavior (Hymenoptera: Formicidae)

This paper studies the production of and the response to the trail in the African urticating ant,Tetramorium aculeatum under a variety of laboratory conditions. The trail was found to contain a complex mix of substances. Two of these components are secreted by the poison gland: The most volatile one is an attractant and increases the ants' linear speed; the other is the trail pheromone, which may act for days on a dry substrate. A third component is present on the last abdominal sternite. It acts as an attractant and a locostimulant and is synergistic of the trail pheromone. The activity of these substances increases with the age of the workers. While following a trail, foragers, even unrewarded, reinforce it with both the poison gland contents and the synergistic compound. The ants follow trails better in darkness than in light. A wetted trail rapidly loses its activity. The article suggests an explanation for the functioning ofT. aculeatum's natural trails, including the role of its different components.     

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.     

Phéromones agrégeant les ouvrières de Myrmica rubra

The workers of Myrmica rubra aggregate around a source of one of their secretions, which can be called ‘alarm pheromone’, and also around workers of Lasius flavus. The mechanism of these aggregations differ.Both L. flavus workers and a solution in liquid paraffin of 3-octanol, one of the mandibular gland compounds, act as an arrestant for the workers of M. rubra. Both Dufour's gland secretion and a source of 3-octanone, the major compound of the mandibular gland secretion, are true attractants.The poison gland secretion, a mixture of 3-octanone and 3-octanol in liquid paraffin and a solution in liquid paraffin of 3-nonanone, a minor mandibular gland compound, all induce klinokinesis. The secretion of the mandibular glands and the secretion of the venom apparatus both cause positive klinokinesis and taxis. These locomotory reactions increase the probability that an object, marked by nest mates with these secretions, will be detected by several workers.When presented alone, 3-octanone is the only attractive compound in the mandibular gland secretion. However, a mixture of 3-octanone and 3-octanol (15 per cent of 3-octanol in the vapour phase) is detected more easily by the ants. The diffusion coefficients of the two compounds are different, and a mixture of these substances creates not only a quantitative but also a qualitative odour gradient. This may explain the synergy of the mixture.     

Monomorium ant's trail pheromones: Glandular source,optimal concentration,longevity and specificity

Many ants use pheromone trails to organize collective foraging. Trail pheromones are produced from different glandular sources and they may be specific to a single species or shared by a number of species. I investigated the source of trail pheromones in three Monomorium ant species: Monomorium niloticum (Emery), M. najrane (Collingwood & Agosti) and M. mayri (Forel). I also examined the optimal concentration, longevity and specificity of the pheromones. M. niloticum and M. najrane secrete trail pheromone from their venom glands, whereas M. mayri secrete trail pheromone from its Dufour's gland. The optimum concentration was 1.0 and 0.1 gaster equivalent (GE)/30 cm trail in M. niloticum, 1.0 GE in M. najrane and 5.0 GE in M. mayri. Longevity of the optimal concentration was about one day for all species. There is no species specificity among the three species of Monomorium in their trail pheromone.     

An Overlooked Mandibular-Rubbing Behavior Used during Recruitment by the African Weaver Ant,Oecophylla longinoda

In Oecophylla, an ant genus comprising two territorially dominant arboreal species, workers are known to (1) use anal spots to mark their territories, (2) drag their gaster along the substrate to deposit short-range recruitment trails, and (3) drag the extruded rectal gland along the substrate to deposit the trails used in long-range recruitment. Here we study an overlooked but important marking behavior in which O. longinoda workers first rub the underside of their mandibles onto the substrate, and then—in a surprising posture—tilt their head and also rub the upper side of their mandibles. We demonstrate that this behavior is used to recruit nestmates. Its frequency varies with the rate at which a new territory, a sugary food source, a prey item, or an alien ant are discovered. Microscopy analyses showed that both the upper side and the underside of the mandibles possess pores linked to secretory glands. So, by rubbing their mandibles onto the substrate, the workers probably spread a secretion from these glands that is involved in nestmate recruitment.     

Chemical and behavioural studies of the trail-following pheromone in the leaf-cutting ant Atta opaciceps,Borgmeier (Hymenoptera: Formicidae)

To understand the significance of the trail pheromone used in chemical communication of the leaf-cutting ants Atta opaciceps we investigated, under laboratory conditions, the trail-following behaviour of different castes. We observed a clear behavioural discrimination of conspecific venom gland extract of foraging ants from those of other species. Additionally, we determined the pheromone composition of A. opaciceps venom gland secretion using a two-dimensional gas chromatography coupled with mass spectrometry. Chemical analyses revealed the presence of three nitrogen-containing compounds, identified as 2,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine and methyl 4-methylpyrrole-2-carboxylate (M4MPC). Four different bioassays performed with workers from different castes of A. opaciceps suggested that the trail pheromone elicits the trail-following behaviour in conspecifics of all castes, but the foragers respond more strongly to their own pheromone than to that of other castes (gardeners, generalists and soldiers). In addition, A. opaciceps foragers follow the trails made with the venom gland extracts of the unrelated Acromyrmex subterraneus subterraneus foragers as well as they follow the trails made with their own venom gland extract. M4MPC was identified to be the most abundant and the most behaviourally active component of the venom gland extract of A. opaciceps foragers.     

Dufour gland secretions of Myrmica rugulosa and Myrmica schencki workers

The chemical composition and behavioural activities of the secretions of the Dufour glands of Myrmica rugulosa and M. schencki have been studied, as part of an extended study on Myrmica ants. Chemically, the Dufour gland of M. rugulosa is filled with a mixture of hydrocarbons dominated by straight chain alkanes and alkenes with 13 to 19 carbon atoms, as found in M. rubra. Significant quantities of (Z,E)-α-farnesene and its homologues, homofarnesene and bishomofarnesene, are also present. In M. schencki, the major compounds present are homofarnesene and bishomofarnesene. In both species, the very volatile portion of the Dufour gland secretion is identical to that analysed in M. rubra. From an ethological point of view, this very volatile part is efficient in attracting workers at a distance (6 to 8 cm) and in decreasing their wandering movements. No specificity was observed when performing cross-tests with Dufour glands freshly isolated from workers of other Myrmica species, but obvious specificities were detected when testing the less volatile part of the Dufour glands' contents, known to be used for marking newly discovered areas.