GSM 900 MHz radiation inhibits ants' association between food sites and encountered cues

The kinetics of the acquisition and loss of the use of olfactory and visual cues were previously obtained in six experimental colonies of the ant Myrmica sabuleti meinert 1861, under normal conditions. In the present work, the same experiments were conducted on six other naive identical colonies of M. sabuleti, under electromagnetic radiation similar to those surrounding GSM and communication masts. In this situation, no association between food and either olfactory or visual cues occurred. After a recovery period, the ants were able to make such an association but never reached the expected score. Such ants having acquired a weaker olfactory or visual score and still undergoing olfactory or visual training were again submitted to electromagnetic waves. Not only did they lose all that they had memorized, but also they lost it in a few hours instead of in a few days (as under normal conditions when no longer trained). They kept no visual memory at all (instead of keeping 10% of it as they normally do). The impact of GSM 900 MHz radiation was greater on the visual memory than on the olfactory one. These communication waves may have such a disastrous impact on a wide range of insects using olfactory and/or visual memory, i.e., on bees.     

Effect of Short-Term GSM Radiation at Representative Levels in Society on a Biological Model: The Ant Myrmica sabuleti

Well-controlled electromagnetic exposure conditions were set up at a representative societal GSM radiation intensity level, 1.5 V/m, which is the legally allowed level in Brussels. Two nests of the ant species Myrmica sabuleti were repeatedly irradiated during 10 min. before their behavior was observed, based on the analysis of the ant trajectories. Under these exposure conditions, behavioral effects were detected. The ants’ locomotion slightly changed. The ants’ orientation towards their attractive alarm pheromone statistically became of lower quality. The ants still presented their trail following behavior but less efficiently. In this controversial issue, ants could be considered as possible bioindicators.     

An ambiguous function of an alarm pheromone in the collective displays of the Australian meat ant,Iridomyrmex purpureus

Alarm pheromones, which have been documented in many species of ants, are thought to elicit responses related to aggressive or defensive behaviour. The volatile odour 6-methyl-5-hepten-2-one is described as an alarm pheromone in several species of ants, including the Australian meat ant, Iridomyrmex purpureus. The alarm pheromone is released by displaying workers that aggregate in the characteristic collective display grounds, located mid-way between colonies or near contested food trees. Workers are typically more aggressive at the latter location, and the alarm pheromone may regulate the collective level of aggression. We investigated this possibility by exposing displaying workers to synthesised alarm pheromone 6-methyl-5-hepten-2-one in a field experiment, and measuring their aggressive behaviour. We found no evidence that exposure to synthesised alarm pheromone caused changes in the aggressive level of workers. Subsequent field experiments revealed that the pheromone functions as an attractant, thereby increasing the density of displaying workers. More densely populated workers also display more aggressively, indicating that the interaction rate of displaying workers may determine the level of aggression in collective displays. This underlying mechanism can explain why displaying ants are more aggressive at the more densely populated food-tree locations than those displaying at locations midway between two neighbouring colony nest sites.     

Alate production in an aphid in relation to ant tending and alarm pheromone

1. Winged dispersal is vital for aphids as predation pressure and host plant conditions fluctuate. 2. Ant‐tended aphids also need to disperse, but this may represent a cost for the ants, resulting in an evolutionary conflict of interest over aphid dispersal. 3. The combined effects of aphid alarm pheromone, indicating predation risk, and ant attendance on the production of winged aphids were examined in an experiment with Aphis fabae (Homoptera: Aphididae) (Scopoli 1763) aphids and Lasius niger (Formicidae: Formicinae) (Linné, 1758) ants. 4. This study is the first to investigate the joint effects of alarm pheromone and ant attendance, and also the first to detect an influence of alarm pheromone on the production of winged morphs in A. fabae. 5. After a period of 2 weeks, it was found that aphid colonies exposed to intermittent doses of alarm pheromone produced more winged individuals, whereas ant tending had the opposite effect. The effects were additive on a log scale, and ant attendance had a greater proportional influence than exposure to alarm pheromone. A tentative conclusion is that ants have gained the upper hand in an evolutionary conflict about aphid dispersal.     

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.     

Trail-following responses ofTapinoma simrothi (Formicidae: Dolichoderinae) to pygidial gland extracts

Summary The pygidial (anal) gland was found to be the source of trail pheromone in the antTapinoma simrothi. Bioassays conducted with fractionated pygidial gland secretion indicated that the fraction containing iridodials and iridomyrmecin is responsible for the trail pheromone activity. Thus workers ofT. simrothi may utilize the same glandular exudate for alarm and trail following. At high emission rates from a point source, the ants responded in alarm, e.g., rushed to the source with open mandibles and raised abdomen. When concentrations were low and drawn as a line, the ants followed the secretion calmly. Trails ofT. simrothi are long-lived, having a biological half-life of 10 to 19 days. Quantitative studies of the evaporation rates of the iridodials by gas chromatography resulted in a half-life of 11 days, agreeing with the biological data. The implications of the use of the same glandular secretion for alarm and food recruitments are discussed.     

Ants adjust their pheromone deposition to a changing environment and their probability of making errors

Animals must contend with an ever-changing environment. Social animals, especially eusocial insects such as ants and bees, rely heavily on communication for their success. However, in a changing environment, communicated information can become rapidly outdated. This is a particular problem for pheromone trail using ants, as once deposited pheromones cannot be removed. Here, we study the response of ant foragers to an environmental change. Ants were trained to one feeder location, and the feeder was then moved to a different location. We found that ants responded to an environmental change by strongly upregulating pheromone deposition immediately after experiencing the change. This may help maintain the colony''s foraging flexibility, and allow multiple food locations to be exploited simultaneously. Our treatment also caused uncertainty in the foragers, by making their memories less reliable. Ants which had made an error but eventually found the food source upregulated pheromone deposition when returning to the nest. Intriguingly, ants on their way towards the food source downregulated pheromone deposition if they were going to make an error. This may suggest that individual ants can measure the reliability of their own memories and respond appropriately.     

The response of grass-cutting ants to natural and synthetic versions of their alarm pheromone

The responses of the grass‐cutting ants Atta bisphaerica (Forel) and Atta capiguara (Gonçalves) to the main components of their alarm pheromones were examined in simple field bioassays. Both species react most strongly to 4‐methyl‐3‐heptanone, which causes the full range of alarm behaviour and a large increase in the number of individuals near the sources. In later experiments with A. capiguara, this increase was found to be due primarily to attraction, with some arrestment also occurring. The ant response to 4‐methyl‐3‐heptanone was compared with that to crushed heads and to that with whole ants with crushed heads. The pheromone 4‐methyl‐3‐heptanone by itself stimulates the same level of attraction as crushed heads, but results in far less alarm behaviour and arrests fewer ants. Whole ants with crushed heads attract a greater number of ants than the other sources and also cause more alarm behaviour. Bodies alone attract ants, but do not result in alarm behaviour. The main component in both species is the same, supporting the view that alarm pheromones lack species specificity. However, it appears that other components may also be important either as synergists of the main compound, or by stimulating behaviours that would not be observed in its absence.     

More to legs than meets the eye: Presence and function of pheromone compounds on heliothine moth legs

Chemical communication is ubiquitous in nature and chemical signals convey species-specific messages. Despite their specificity, chemical signals may not be limited to only one function. Identifying alternative functions of chemical signals is key to understanding how chemical communication systems evolve. Here, we explored alternative functions of moth sex pheromone compounds. These chemicals are generally produced in, and emitted from, dedicated sex pheromone glands, but some have recently also been found on the insects' legs. We identified and quantified the chemicals in leg extracts of the three heliothine moth species Chloridea (Heliothis) virescens, Chloridea (Heliothis) subflexa and Helicoverpa armigera, compared their chemical profiles and explored the biological function of pheromone compounds on moth legs. Identical pheromone compounds were present on the legs in both sexes of all three species, with no striking interspecies or intersex differences. Surprisingly, we also found pheromone-related acetate esters in leg extracts of species that lack acetate esters in their female sex pheromone. When we assessed gene expression levels in the leg tissue, we found known and putative pheromone-biosynthesis genes expressed, which suggests that moth legs may be additional sites of pheromone production. To determine possible additional roles of the pheromone compounds on legs, we explored whether these may act as oviposition-deterring signals, which does not seem to be the case. However, when we tested whether these chemicals have antimicrobial properties, we found that two pheromone compounds (16:Ald and 16:OH) reduce bacterial growth. Such an additional function of previously identified pheromone compounds likely coincides with additional selection pressures and, thus, should be considered in scenarios on the evolution of these signals.     

Polyethism and nestmate recognition in the alarm reaction of Atta leaf-cutting ants

Abstract.  Ethological studies are conducted under laboratory conditions using workers of Atta sexdens sexdens and Atta opaciceps collected from field colonies to investigate the mechanisms involved in the alarm response and intra-specific recognition in leaf-cutting ants. Hexane extracts from the heads of gardeners and generalist workers elicit higher levels of alarm response in foragers from the same colony than do mandibular gland extracts from foragers and soldiers, indicating that gardeners, generalists and foragers are primarily responsible for the production of alarm pheromone. Foragers subjected to extracts from non-nestmates exhibit significantly greater alarm responses than are induced by similar extracts derived from nestmate workers, suggesting that the alarm pheromone may have a role in nestmate recognition.     

Spatial representation of alarm pheromone information in a secondary olfactory centre in the ant brain

Pheromones play major roles in intraspecific communication in many animals. Elaborated communication systems in eusocial insects provide excellent materials to study neural mechanisms for social pheromone processing. We previously reported that alarm pheromone information is processed in a specific cluster of glomeruli in the antennal lobe of the ant Camponotus obscuripes. However, representation of alarm pheromone information in a secondary olfactory centre is unknown in any animal. Olfactory information in the antennal lobe is transmitted to secondary olfactory centres, including the lateral horn, by projection neurons (PNs). In this study, we compared distributions of terminal boutons of alarm pheromone-sensitive and -insensitive PNs in the lateral horn of ants. Distributions of their dendrites largely overlapped, but there was a region where boutons of pheromone-sensitive PNs, but not those of pheromone-insensitive PNs, were significantly denser than in the rest of the lateral horn. Moreover, most of a major type of pheromone-sensitive efferent neurons from the lateral horn extended dendritic branches in this region, suggesting specialization of this region for alarm pheromone processing. This study is the first study to demonstrate the presence of specialized areas for the processing of a non-sexual, social pheromone in the secondary olfactory centre in any animal.     

A blend of formic acid,benzoic acid,and aliphatic alkanes mediates alarm recruitment responses in western carpenter ants,Camponotus modoc

Formicine ants in distress spray alarm pheromone which typically recruits nestmates for help. Studying the western carpenter ant, Camponotus modoc Wheeler (Hymenoptera: Formicidae), our objectives were to (1) determine the exocrine glands that contain alarm recruitment pheromone, (2) identify the key alarm recruitment pheromone components, and (3) ascertain the pheromone components that are discharged by distressed ants. In Y-tube olfactometer experiments, extracts of poison glands, but not of Dufour’s glands, elicited anemotactic responses from worker ants. Gas chromatographic-mass spectrometric analyses of poison gland extracts revealed the presence of (1) aliphatic alkanes (undecane, tridecane, pentadecane, heptadecane), (2) aliphatic alkenes [(Z)-7-pentadecene, (Z)-7- and (Z)-8-heptadecene], (3) two acids (formic, benzoic), and (4) other oxygenated compounds (hexadecan-1-ol, hexadecyl formate, hexadecyl acetate). Testing the responses of worker ants in Y-tube olfactometers to complete and partial synthetic blends of these compounds revealed that the acids and the alkanes are essential alarm pheromone components. In two-choice arena bioassays, micro-locations treated with synthetic alarm pheromone recruited worker ants. Acids and alkanes were abundant in the poison gland and the Dufour’s gland, respectively, suggesting that the alarm pheromone components originate from both glands. Moreover, alarm pheromone sprays of ants differed in that all sprays contained formic acid but only some also contained alkanes, implying that ants can independently discharge the content of either one or both glands in accordance with the type of distress incident they experience.     

Behavioral responses to the alarm pheromone of the ant Camponotus obscuripes (Hymenoptera: Formicidae)

The alarm pheromone of the ant Camponotus obscuripes (Formicinae) was identified and quantified by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Comparisons between alarm pheromone components and extracts from the major exocrine gland of this ant species revealed that the sources of its alarm pheromone are Dufour's gland and the poison gland. Most components of Dufour's gland were saturated hydrocarbons. n-Undecane comprised more than 90% of all components and in a single Dufour's gland amounted to 19 microg. n-Decane and n-pentadecane were also included in the Dufour's gland secretion. Only formic acid was detected in the poison gland, in amounts ranging from 0.049 to 0.91 microl. This ant species releases a mixture of these substances, each of which has a different volatility and function. When the ants sensed formic acid, they eluded the source of the odor; however, they aggressively approached odors of n-undecane and n-decane, which are highly volatile. In contrast, n-pentadecane, which has the lowest volatility among the identified compounds, was shown to calm the ants. The volatilities of the alarm pheromone components were closely related to their roles in alarm communication. Highly volatile components vaporized rapidly and spread widely, and induced drastic reactions among the ants. As these components became diluted, the less volatile components calmed the excited ants. How the worker ants utilize this alarm communication system for efficient deployment of their nestmates in colony defense is also discussed herein.     

Hierarchical establishment of information sources during foraging decision-making process involving Acromyrmex subterraneus (Forel, 1893) (Hymenoptera,Formicidae)

During foraging, worker ants are known for making use of many information sources to guide themselves in external environments, especially individual (memory) and social (trail pheromone) information. Both kinds of information act in a synergic way, keeping the foraging process efficient and organized. However, when social and individual information is conflicting face a trail bifurcation, it is necessary to establish a hierarchical order so prioritizing one of them. This study aims to verify which information (social or individual) is prioritized by Acromyrmex subterraneus workers when facing a bifurcation in a Y-trail system. Only one branch of the Y-trail leads to food resource and it had a section covered by filter paper where trail pheromone was deposited by workers. Pheromone deposition was here estimated by worker flow. After an individually marked forager (target-worker) made 1, 3 or 5 trips to the food resource, the filter paper was transferred to the branch which did not lead to the food. The time spent by target workers on branch selection and their right choice (branch with food) frequency were registered. Regardless of the target worker's previous trips to the resource, right choice frequency stood over 70%. In addition, the number of previous trips did not influence the time spent on decision making. However, the higher the flow of workers, the longer the time spent on decision making. By simulating a situation with conflicting information, it was possible to verify that a hierarchical order is established by A. subterraneus, which prioritized individual information (memory).     

Removal of the vomeronasal organ blocks the stress-induced hyperthermia response to alarm pheromone in male rats

Previously, we reported that male Wistar rats release alarm pheromone from their perianal region, which aggravates stress-induced hyperthermia (SIH) in pheromone-recipient rats. The subsequent discovery that this pheromone could be trapped in water enabled us to expose recipients to the pheromone in their home cages. Despite its apparent influence on autonomic and behavioral functions, we still had no clear evidence as to whether the alarm pheromone was perceived by the main olfactory system (MOS) or by the vomeronasal system. In this study, we investigated this question by exposing 3 types of recipients to alarm pheromone in their home cages: intact males (Intact), vomeronasal organ-excised males (VNX), and sham-operated males (Sham). The Intact and Sham recipients showed aggravated SIH in response to alarm pheromone, whereas the VNX recipients did not. In addition, the results of the habituation/dishabituation test and soybean agglutinin binding to the accessory olfactory bulb verified the complete ablation of the vomeronasal organ (VNO) with a functional MOS in the pheromone recipients. These results strongly suggest that male rats perceive alarm pheromone with the VNO.     

Foraging Trade-offs in Fathead Minnows (Pimephales promelas,Osteichthyes, Cyprinidae): Acquired Predator Recognition in the Absence of an Alarm Response

Pike-naive fathead minnows (Pimephales promelas) were fed ad libitum or deprived of food for 12, 24, or 48 h and then exposed to either conspecific alarm pheromone or distilled water and the odour of a predatory northern pike (Esox lucius). Minnows fed ad libitum or deprived for 12 h showed a stereotypic alarm response to the alarm pheromone (increased time under cover objects and increased occurrence of dashing and freezing behaviour); those deprived of food for 24 h showed a significantly reduced alarm response, while those deprived of food for 48 h did not differ significantly from the minnows exposed to a distilled water control. Upon subsequent testing in an Opto-Varimex activity meter, all groups initially exposed to alarm pheromone and pike odour exhibited an alarm response when exposed to pike odour alone. Those initially conditioned with distilled water and pike odour did nor show an alarm response to pike odour alone. These results demonstrate that there exists a significant trade-off between hunger level and predator-avoidance behaviour in fathead minnows and that minnows can learn the chemical cues of a predatory northern pike through association with alarm pheromone even in the absence of an observable alarm response.     

The capacity of a Myrmica ant nest to support a predacious species of Maculinea butterfly

Summary Caterpillars of Maculinea arion are obligate predators of the brood of Myrmica sabuleti ants. In the aboratory, caterpillars eat the largest available ant larvae, although eggs, small larvae and prepupae are also palatable. This is an efficient way to predate. It ensures that newly-adopted caterpillars consume the final part of the first cohort of ant brood in a nest, before this pupates in early autumn and becomes unavailable as prey. At the same time, the fixed number of larvae in the second cohort is left to grow larger before being killed in late autumn and spring. Caterpillars also improve their feeding efficiency by hibernating for longer than ants in spring, losing just 6% of their weight while the biomass of ant larvae increases by 27%. Final instar caterpillars acquire more than 99% of their ultimate biomass in Myrmica nests, growing from 1.3 mg to an estimated 173 mg. A close correlation was found between the weights of caterpillars throughout autumn and the number of large ant larvae they had eaten. This was used to calculate the number of larvae eaten in spring, allowing both for the loss of caterpillar weight during winter and the increase in the size of their prey in spring. It is estimated that 230 of the largest available larvae, and a minimum nest size of 354 M. sabuleti workers, is needed to support one butterfly. Few wild M. sabuleti nests are this large: on one site, it was estimated that 85% of nests were too small to produce a butterfly, and only 5% could support two or more. This prediction was confirmed by the mortalities of 376 caterpillars in 151 wild M. sabuleti nests there. Mortalities were particularly high in nests that adopted more than two caterpillars, apparently due to scramble competition and starvation in autumn. Survival was higher than predicted in wild nests that adopted one caterpillar. These caterpillars seldom exhaust their food before spring, when there is intense competition among Myrmica for nest sites. Ants often desert their nests in the absence of brood, leaving the caterpillar behind. Vacant nests are frequently repopulated by a neighbouring colony, carrying in a fresh supply of brood. Maculinea arion caterpillars have an exceptional ability to withstand starvation, and sometimes survive to parasitize more than one Myrmica colony. Despite these adaptations, predation is an inefficient way to exploit the resources of a Myrmica nest. By contrast, Maculinea rebeli feeds mainly at a lower trophic level, on the regurgitations of worker ants. Published data show that Myrmica nests can support 6 times more caterpillars of Maculinea rebeli than of M. arion in the laboratory. This is confirmed by field data.     

Spatial and temporal variation in pheromone composition of ant foraging trails

Many social insects use pheromones to communicate and coordinatetheir activities. Investigation of intraspecific differencesin pheromone use is a new area of social insect research. Forexample, interindividual variation in alarm pheromone contenthas been found in physical castes of polymorphic ants. Manyant species use multiple trail pheromones. Here we present novelresearch into trail pheromone variations between behavioralsubcastes of pharaoh ants, Monomorium pharaonis. Monomoriumpharaonis is attracted to trail pheromones found in its poisonglands (monomorines) and Dufour's glands (faranal). We showthat the most abundant monomorines, I (M1) and III (M3), canbe readily detected in pheromone trails. A behaviorally distinctsubcaste known as "pathfinder" foragers can relocate long-livedpheromone trails. Chemical analysis showed that pathfinder foragershad low M3:M1 ratios (mean 3.09 ± 1.53, range 1.03–7.10).Nonpathfinder foragers had significantly greater M3:M1 ratios(38.3 ± 60.0, range 3.54–289). We found that M3:M1ratio did not differ between foragers of different age but wascorrelated with behavioral subcaste at all ages. The relativeabundance of M3:M1 on foraging trails ranged from 3.03–41.3over time during pheromone trail build-up. M3:M1 ratio alsovaried spatially throughout trail networks, being lowest ontrail sections closest to a food source (M3:M1 = 1.9–3.61)and highest near the nest (M3:M1 = 67–267). Our resultsindicate a functional role for differences in pheromone trailcomposition, whereby pathfinder foragers might preferentiallymark sections of pheromone trail networks for future exploration.     

Pheromone-sensitive glomeruli in the primary olfactory centre of ants

Tremendous evolutional success and the ecological dominance of social insects, including ants, termites and social bees, are due to their efficient social organizations and their underlying communication systems. Functional division into reproductive and sterile castes, cooperation in defending the nest, rearing the young and gathering food are all regulated by communication by means of various kinds of pheromones. No brain structures specifically involved in the processing of non-sexual pheromone have been physiologically identified in any social insects. By use of intracellular recording and staining techniques, we studied responses of projection neurons of the antennal lobe (primary olfactory centre) of ants to alarm pheromone, which plays predominant roles in colony defence. Among 23 alarm pheromone-sensitive projection neurons recorded and stained in this study, eight were uniglomerular projection neurons with dendrites in one glomerulus, a structural unit of the antennal lobe, and the remaining 15 were multiglomerular projection neurons with dendrites in multiple glomeruli. Notably, all alarm pheromone-sensitive uniglomerular projection neurons had dendrites in one of five 'alarm pheromone-sensitive (AS)' glomeruli that form a cluster in the dorsalmost part of the antennal lobe. All alarm pheromone-sensitive multiglomerular projection neurons had dendrites in some of the AS glomeruli as well as in glomeruli in the anterodorsal area of the antennal lobe. The results suggest that components of alarm pheromone are processed in a specific cluster of glomeruli in the antennal lobe of ants.     

Pheromone trail decay rates on different substrates in the Pharaoh's ant, Monomorium pharaonis

Abstract. Many ants use pheromone trails to organize collective foraging. This study investigated the rate at which a well‐established Pharaoh's ant, Monomorium pharaonis (L.), trail breaks down on two substrates (polycarbonate plastic, newspaper). Workers were allowed to feed on sucrose solution from a feeder 30 cm from the nest. Between the nest and the feeder, the trail had a Y‐shaped bifurcation. Initially, while recruiting to and exploiting the feeder, workers could only deposit pheromone on the branch leading to the feeder. Once the trail was established (by approximately 60 ants per min for 20 min), the ants were not allowed to reinforce the trail and were given a choice between the marked and unmarked branches. The numbers of ants choosing each branch were counted for 30 min. Initially, most went to the side on which pheromone had been deposited (80% and 70% on the plastic and paper substrates, respectively). However, this decayed to 50% within 25 min for plastic and 8 min for paper. From these data, the half‐life times of the pheromone are estimated as approximately 9 min and 3 min on plastic and paper, respectively. The results show that, for M. pharaonis, trail decay is rapid and is affected strongly by trail substrate.