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Pheromones are perhaps the most common form of intraspecific communication in the animal kingdom and used in various contexts. Their modulatory potential on cognitive processes has been demonstrated in both vertebrates and invertebrates. Particularly interesting in this regard are social insects, due to their extensive use of pheromones to organise collective behaviour. Recruitment pheromones might be expected to encourage learning, but could also hinder learning due to a blocking effect, whereby the pheromone already partially predicts the reward, hindering further cues being associated with the reward. Here, we use free-running learning assays using realistic pheromone strength to test for a modulation effect on learning in the black garden ant Lasius niger. We found no evidence that learning in three modalities (olfactory, visual, and spatial) is affected by the presence of a realistic pheromone trail. Interestingly, this is in contrast to findings in honeybees. The fact that associative learning does not seem to be influenced by recruitment pheromone in L. niger and reportedly the Argentine ant, while it is in honeybees, the possibly best-studied social insect species, is noteworthy. We speculate that a species-specific importance of social information use could drive modulatory effects of pheromones on a wide range of cognitive processes. Significance statement: Pheromones have been shown to modulate associative learning in a variety of animals. Among social insects, attractive pheromone has been found to enhance associative olfactory learning in honeybees but not in ants. In ants, recruitment pheromone predicts a food source; therefore, it might hinder learning of a new cue for a food reward. We use a free-running learning assay to test for an effect of trail pheromone on associative learning in three different modalities—olfactory, spatial, visual—in Lasius niger, but find no evidence of any effect. Our learning assay demonstrated fast olfactory learning, moderate spatial learning, and no visual learning after only one training visit. Based on our findings, and findings in two other ant species, we speculate that the ecological foraging conditions of mass-recruiting ants, i.e. following a trail, have not favoured a modulation potential of recruitment pheromone opposed to attractive pheromone in honeybees. [ABSTRACT FROM AUTHOR]

Social behaviours in termites are closely related to the chemical communication between individuals. It is well known that foraging worker termites can use trail pheromones to orient and locomote along trails so as to take food resources back to the nest. However, it is still unclear how termites recognize trail pheromones. Here, we cloned and sequenced the cGMP‐dependent protein kinase (PKG) gene from the termite Reticulitermes chinensis Snyder, and then examined the response of termites to trail pheromones after silencing PKG through RNA interference. We found that PKG knockdown impaired termite ability to follow trail pheromones accurately and exhibited irregular behavioural trajectories in response to the trail pheromone in the termite R. chinensis. Our locomotion assays further showed that PKG knockdown significantly increased the turn angle and angular velocity in the termite R. chinensis. These findings help us better understanding the molecular regulatory mechanism of foraging communications in termites. [ABSTRACT FROM AUTHOR]

Pollinators provide a key ecosystem service that can be influenced by predation and predator avoidance. However, it was unclear whether pollinators can avoid predators by eavesdropping, intercepting predator signals. Using a natural species assemblage, we show that a bee can eavesdrop on and avoid the trail pheromone of a sympatric ant, while foraging on a native plant. The giant Asian honeybee, Apis dorsata, avoided Calliandra haematocephala inflorescences with live weaver ants, Oecophylla smaragdina. Although few foraging bees were attacked, ants killed the bee in almost a third of attacks. Ant presence alone significantly reduced bee floral visits. Bees showed nearly equal avoidance of live ants and trail pheromone extracts, demonstrating that olfactory eavesdropping alone can elicit full avoidance. We then used GC-MS to analyse compounds deposited by ants walking and laying trail pheromone. The most abundant compounds were all trail pheromone components. However, bees did not avoid the most abundant and conspicuous trail pheromone compound, heneicosane. Foragers may instead detect a mixture of different trail pheromone compounds. Our results contribute to a growing understanding of how public information about predators and competitors can shape food webs, and show that pollinators can tap into the private signals of predators and use this information to their advantage.

Pollinators provide a key ecosystem service that can be influenced by predation and predator avoidance. However, it was unclear whether pollinators can avoid predators by eavesdropping, intercepting predator signals. Using a natural species assemblage, we show that a bee can eavesdrop on and avoid the trail pheromone of a sympatric ant, while foraging on a native plant. The giant Asian honeybee, Apis dorsata, avoided Calliandra haematocephala inflorescences with live weaver ants, Oecophylla smaragdina. Although few foraging bees were attacked, ants killed the bee in almost a third of attacks. Ant presence alone significantly reduced bee floral visits. Bees showed nearly equal avoidance of live ants and trail pheromone extracts, demonstrating that olfactory eavesdropping alone can elicit full avoidance. We then used GC-MS to analyse compounds deposited by ants walking and laying trail pheromone. The most abundant compounds were all trail pheromone components. However, bees did not avoid the most abundant and conspicuous trail pheromone compound, heneicosane. Foragers may instead detect a mixture of different trail pheromone compounds. Our results contribute to a growing understanding of how public information about predators and competitors can shape food webs, and show that pollinators can tap into the private signals of predators and use this information to their advantage.

The pre-excavation activity of the neonate larvae of Cactoblastis cactorum (Lepidoptera: Pyralidae) is typically confined to an arena that encircles the base of their egg stick. If the caterpillars are unable to penetrate the host plant within the arena, they strike off en masse in search of a more favorable site, marking their pathway with secretions from their mandibular glands. One component of this secretion, 4-hydroxy-2-oleoylcyclohexane-1,3-dione (an acylcyclohexanedione, ACHD), has been previously shown to function as a trail pheromone. In this paper, we report the characterization, synthesis, and bioassays of a family of 3-acyl fatty acid methyl esters (which we named cactoblastins), a chemically distinct group of mandibular gland compounds that also elicit trail following behavior. The relative effectiveness in eliciting trail following of the ACHD and six, chemically distinct, synthetic cactoblastins was determined. The most bioactive of the cactoblastins was also compared to whole mandibular gland extract to assess its ability to disrupt the aggregative behavior of the neonates and to serve as a biorational alternative to pesticides for managing invasive populations of the caterpillar. [ABSTRACT FROM AUTHOR]

Ants (Hymenoptera: Formicidae), especially the Argentine ant, Linepithema humile (Mayr), can be significant nuisance pests in urban and suburban environments. Conventional interventions have primarily relied on the use of chemical insecticides, namely fipronil and bifenthrin, applied as residual, contact treatments around the outside perimeter of infested structures. Despite tightening regulation limiting the scope of insecticide applications in urban settings, dependence on these products to manage ants continues, resulting in significant water contamination. The U.S. EPA, in response, has further restricted the use patterns of many insecticides used for ant control in professional and over-the-counter markets. The purpose of this review is to summarize the relevant literature associated with controlling nuisance pest ants, with emphasis on L. humile, without the use of liquid broadcast applications of EPA-registered insecticides while focusing on low-impact, alternative (to broadcast applications) pest control methods. Specific subsections include Trail Pheromone; Use of Behavior-Modifying Chemicals; Mass Trapping; Hydrogels, “Virtual” Baiting, and Exceedingly-Low Bait Concentrations; Food Source Reduction; Deterrents; and RNA Interference (RNAi).

Trail pheromones deposited by ants lead nestmates to food sources. Based on previous evidence that the trail pheromone of the carpenter ant Camponotus modoc originates from the hindgut, our objective in this study was to identify the key component(s) of the pheromone. We collected C. modoc colonies from conifer forests and maintained them in an outdoor enclosure near our laboratory for chemical analyses and behavioral experiments. In gas chromatographic-electroantennographic detection and gas chromatography-mass spectrometric analyses of worker ant hindgut extracts, we identified five candidate components: 2,4-dimethylhexanoic acid, 2,4-dimethyl-5-hexanolide, pentadecane, dodecanoic acid and 3,4-dihydro-8-hydroxy-3,5,7-trimethylisocoumarin. In a series of trail-following experiments, ants followed trails of synthetic 2,4-dimethyl-5-hexanolide, a blend of the five compounds, and hindgut extract over similar distances, indicating that the hexanolide accounted for the entire behavioral activity of the hindgut extract. The hexanolide not only mediated orientation of C. modoc foragers on trails, it also attracted them over distance, indicating a dual function. Further analyses and bioassays with racemic and stereoselectively synthesized hexanolides revealed that the ants produce, and respond to, the (2S,4R,5S)-stereoisomer. The same stereoisomer is a trail pheromone component in several Camponotus congeners, indicating significant overlap in their respective trail pheromone communication systems. [ABSTRACT FROM AUTHOR]

The Japanese pavement ant Tetramorium tsushimae Emery (Hymenoptera: Formicidae) has a mass recruitment system for foraging. We successfully separated the trail pheromone from the ant worker extract by preparative gas chromatography, and estimated it as methyl 6-methylsalicylate based on the Kováts retention indices and mass spectra, which coincided with those of the synthetic compound. We also confirmed that the synthetic methyl 6-methylsalicylate elicited a trail-following response in the workers even at approximately 0.3 pg/cm of the trail line. The strength for this response was similar to the estimated level of trail pheromone in the abdominal extracts of workers. It seems likely that the glandular source was the poison gland, because poison gland extract evoked trail-following responses in significantly more workers than other gland extracts. We therefore identified the trail pheromone of this ant species as methyl 6-methylsalicylate and tentatively identified its source as the poison gland. [ABSTRACT FROM AUTHOR]

The little fire ant (LFA), Wasmannia auropunctata (Hymenoptera: Formicidae), is native to the neotropics, but has become one of the world's most widespread and destructive invasive ants. In Hawaii, LFA was first discovered in 1999 on the Big Island and since then has rapidly spread to neighboring islands, causing ecological and economic damage. LFA can develop fully functional nests on the ground and arboreally, and their foraging and retrieval of food resources is facilitated by a well-developed recruitment system. LFA were found to form recruitment trails on epiphytic moss growing on macadamia nut trees. As a first step to identify LFA recruitment pheromone components, we tested the LFA worker trail-following response to naturally marked epiphytic moss trails. Significantly more LFA workers placed on a natural trail followed the trail and made 90° turns to continue following the trail compared to when they were placed on a fake trail that had no trail marking substance(s). In laboratory choice assays using hexane extracts of moss with and without LFA trail, LFA workers preferred to follow a trail drawn with a hexane extract of moss that had a recruitment trail over a trail drawn with a hexane extract of moss only. Our results confirm that LFA workers readily follow a trail marking substance(s) laid down on epiphytic moss. [ABSTRACT FROM AUTHOR]

In this study, we explored the feeding behaviour of the invasive garden ant Lasius neglectus. In particular, we investigated its ability to select the more profitable resource in a binary choice and its pheromonal trail marking. When facing a choice between two different energy sources, workers were rapidly recruited to the most profitable one, although both the speed of the recruitment and the number of ants varied considerably with the difference between the solutions. When facing two identical sources, workers were massively recruited onto one of the two in 80% of tests, whereas in the remaining 20% the workforce was split equally between the two. In the second experiment, we supplied a single food source and then assessed if the number of marks per ant was affected by solution concentration and direction of movement (nestward or foodward), and if it varied over time. Marking activity increased with solution concentration, was more intense in nestward‐moving ants, and decreased over time. All these effects, although significant, were not pronounced. However, the marking activity of the very first ants visiting the resource was more intense, and this seems to be sufficient to explain the collective selection of the most valuable resource. Finally, marks were not evenly distributed along the trail, but concentrated at some points. The behaviour of L. neglectus is partly comparable to that of Lasius niger, but appears to be more similar to that of other invasive ant species, suggesting a possible primary role of the marking behaviour in influencing the invasiveness of this species. [ABSTRACT FROM AUTHOR]

In this article, I will describe how a simple, curiosity-based experiment to understand how ants are smart enough to choose the shortest path led the exploration of self-organization and swarm-intelligence and resulted in major applications in computer science and optimization algorithms. The focus will be on curiosity, simplicity, interdisciplinarity, and being unmindful of immediate applications. [ABSTRACT FROM AUTHOR]

For social animals, decision-making is influenced by both social information provided by the group, and private information based on the individual’s personal experience. Social insects make excellent study systems for understanding how social and private information is used by individuals to influence their navigational route choice, and thereby influence the collective decision-making strategy of the group. Using colonies of the Australian meat ant, Iridomyrmex purpureus, we demonstrate that when individual workers are trained to a rewarding arm in a Y maze, the trained ants use private information (memory) in route choice when social information (trail pheromone) is experimentally removed and have no preference when private information and social information are in direct conflict with each other. Additional experience did not provide a strong training effect, such that ants returning after their first training trip tended to choose the path they had been trained on (private information) and subsequent trips did not have a significant additional effect on this initial preference. [ABSTRACT FROM AUTHOR]

Ants communicate using a suite of chemicals with a level of sophistication that is inextricably linked to their ecological dominance. The fungus-growing ants have been the focus of chemical ecology studies for decades, especially the leaf-cutting ants. Some create long, conspicuous foraging trails to harvest fresh vegetation used to sustain large farming systems that feed millions of workers. However, of the ca. 250 fungus-growing ant species, most feed detritus rather than fresh material to their gardens, and colony sizes are tens to hundreds of workers. Colonies within the attine genus Cyphomyrmex use distinct methods of agriculture (i.e., yeast and lower fungus agriculture). We compared compounds found in five species from the yeast-growing Cyphomyrmex rimosus group (C. rimosus and C. salvini) and the lower agriculture Cyphomyrmex wheeleri group (C. costatus, C. longiscapus, C. muelleri). Compounds identified were compared with those reported in the literature and mapped onto the attine-ant phylogeny, and glands of origin suggested. There were 10 compounds across five species and two are known alarm compounds, 1-octen-3-o1 and 3-octanol. Of the six farnesenes detected, the most notable was the diversity of gaster-derived compounds in C. salvini and the high abundance of (3Z, 6E)-α-7-ethylhomofarnesene and α-6-bishomofarnesene in the three C. wheeleri group species. We also found 2,5-dimethyl-3-isoamylpyrazine in the heads of yeast-growing species, an unexpected result because pyrazines are known trail substances in other attines. Our results expand our understanding of semiochemicals found in fungus-growing ants and provides a starting point to generate hypotheses for more extensive comparative studies. [ABSTRACT FROM AUTHOR]

Ants deposit trail pheromones that guide nestmates to food sources. We tested the hypotheses that ant community members (Western carpenter ants, Camponotus modoc; black garden ants, Lasius niger; European fire ants, Myrmica rubra) (1) sense, and follow, each other’s trail pheromones, and (2) fail to recognize trail pheromones of allopatric ants (pavement ants, Tetramorium caespitum; desert harvester ants, Novomessor albisetosus; Argentine ants, Linepithema humilis). In gas chromatographic-electroantennographic detection analyses of a six-species synthetic trail pheromone blend (6-TPB), La. niger, Ca. modoc, and M. rubra sensed the trail pheromones of all community members and unexpectedly that of T. caespitum. Except for La. niger, all species did not recognize the trail pheromones of N. albisetosus and Li. humilis. In bioassays, La. niger workers followed the 6-TPB trail for longer distances than their own trail pheromone, indicating an additive effect of con- and hetero-specific pheromones on trail-following. Moreover, Ca. modoc workers followed the 6-TPB and their own trail pheromones for similar distances, indicating no adverse effects of heterospecific pheromones on trail-following. Our data show that ant community members eavesdrop on each other’s trail pheromones, and that multiple pheromones can be combined in a lure that guides multiple species of pest ants to lethal food baits.

Predators may eavesdrop on their prey using innate signals of varying nature. In regards to social prey, most of the prey signals are derived from social communication and may therefore be highly complex. The most efficient predators select signals that provide the highest benefits. Here, we showed the use of eusocial prey signals by the termite-raiding ant Odontoponera transversa. O. transversa selected the trail pheromone of termites as kairomone in several species of fungus-growing termites (Termitidae: Macrotermitinae: Odontotermes yunnanensis, Macrotermes yunnanensis, Ancistrotermes dimorphus). The most commonly predated termite, O. yunnanensis,was able to regulate the trail pheromone component ratios during its foraging activity. The ratio of the two trail pheromone compounds was correlated with the number of termites in the foraging party. (3Z)-Dodec-3-en-1-ol (DOE) was the dominant trail pheromone component in the initial foraging stages when fewer termites were present. Once a trail was established, (3Z,6Z)-dodeca-3,6-dien-1-ol (DDE) became the major recruitment component in the trail pheromone and enabled mass recruitment of nest-mates to the food source. Although the ants could perceive both components, they revealed stronger behavioural responses to the recruitment component, DDE, than to the common major component, DOE. In other words, the ants use the trail pheromone information as an indication of suitable prey abundance, and regulate their behavioural responses based on the changing trail pheromone component. The eavesdropping behaviour in ants therefore leads to an arms race between predator and prey where the species specific production of trail pheromones in termites is targeted by predatory ant species. [ABSTRACT FROM AUTHOR]

The amount of the trail pheromone substance, 3-ethyl-2,5-dimethylpyrazine, of the leaf-cutting ant Atta sexdens sexdens (Hymenoptera: Formicidae) increases with increasing size of the ant from 0 to 35 ng per individual. The compounds 2,5-dimethylpyrazine and trimethylpyrazine are also consistently present. Trails of venom gland extracts are followed with unequal fidelity by different castes. Minor workers follow best, mediums least well. Workers walk sinuously on narrow trails and less sinuously on wider trails up to 9 mm. Trails wider than 9 mm are not followed. The optimum concentration of pheromone on synthetic trails lies between 15 and 150 pg cm-1. Given a choice of concentrations at a trail branch, workers always choose the more concentrated. Workers showed slight preference for a trail made with venom gland secretion from their own, over that from an alien colony, but there is no preference for a trail that contains Dufour gland secretion additionally.

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. [ABSTRACT FROM AUTHOR]