Behavioral and olfactory antennal responses of Solenopsis geminata (Fabricius) (Hymenoptera: Formicidae) workers to their dufour gland secretion

Behavioral and electrophysiological tests were performed to evaluate the responses of workers of the ant Solenopsis geminata (Fabricius) from different size categories to Dufour gland extracts. Morphometric measures based in head widths across eyes were used to determine worker sizes. Trail following response of different worker sizes to Dufour gland extract from workers of different sizes was assessed. For each worker size category olfactory responses to Dufour gland extracts were determined using electroantennography (EAG). Gas chromatography and mass spectrometry (GC-MS) were used to determine the chromatographic profile of Dufour gland secretion for each worker size. Morphometric measures permitted to classify the workers of S. geminata as large, medium and small workers. Medium S. geminata workers displayed a significantly higher behavioral response to Dufour gland extracts produced by medium size workers. Similarly, medium workers showed a significantly higher EAG response to Dufour gland extracts produced by medium sized workers. Chromatographic profile of Dufour gland secretions produced by workers showed that each size category exhibited a characteristic profile of the three main components considered as potential trail pheromone constituents. This work showed that medium workers of S. geminata exhibited a high trail-following behavior as well as a high antennal response to Dufour gland secretion. This and their relative abundance in field foraging areas, suggest that medium-sized workers are specialized in foraging activities.     

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.     

Some factors determining size-matching in the harvester ant Messor barbarus: food type, transfer activity, recruitment rate and size-range

Summary. A study was made of variations in size-matching in M. barbarus during transport of food to the nest. The effects of various factors were studied. Ants showed low selectivity at the food source, with both natural and with baits. This low initial selectivity tended to increase as seed fragments were transported along the foraging-trail to the nest; by the end of the trail, a very high degree of correlation was recorded between ant mass and load mass (r = 0.64, p < 0.001). This increase in correlation between ant mass and load mass may be brought about by exchanges of loads between workers along the length of the foraging trail. We have shown that there exists an inverse relationship between the recruitment rate to a food patch and size-matching. The most important population foragers factors affecting size-matching are the variation in load size, followed by the variation in worker size.     

A field assessment of optimal foraging in ants: trail patterns and seed retrieval by the European harvester ant Messor barbarus

Summary: The ant Messor barbarus is a major seed predator on annual grasslands of the Mediterranean area. This paper is an attempt to relate the foraging ecology of this species to resource availability and to address several predictions of optimal foraging theory under natural conditions of seed harvesting.¶Spatial patterns of foraging trails tended to maximise acquisition of food resources, as trails led the ants to areas where seeds were more abundant locally. Moreover, harvesting activity concentrated on highly frequented trails, on which seeds were brought into the nest in larger numbers and more efficiently, at a higher mean rate per worker.¶The predictions of optimal foraging theory that ants should be more selective in both more resource-rich and more distant patches were tested in the native seed background. We confirm that selectivity of ants is positively related to trail length and thus to distance from the nest of foraged seeds. Conversely, we fail to find a consistent relationship between selectivity and density or species diversity of seed patches. We discuss how selectivity assessed at the colony level may depend on factors other than hitherto reported behavioural changes in seed choice by individual foragers.     

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.     

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.     

Foraging behaviour of harvesting ants determines seed removal and dispersal

Harvesting ants can affect the regeneration of plants through at least two different processes: seed removal and seed dispersal. We analyse the role of different foraging strategies of ants on patterns of seed removal and dispersal by three Messor species with considerable differences in their foraging systems. Messor capitatus workers rarely leave the nest in well-formed columns, while the other two species form foraging trails, with M. bouvieri forming temporary trails and M. barbarus foraging on a stable system of permanent foraging trails. Overall seed intake of M. capitatus colonies is considerably less than that of the two group-foraging species. There are also differences in the size of seeds collected: M. barbarus and M. capitatus harvest similar amounts of large and small seeds, while M. bouvieri harvests small seeds more intensely than large ones, due to the smaller size of the worker caste. The three Messor species differ in the percent of seed dropping of the different seed type and in the seed dispersal distance. Moreover, M. bouvieri and M. capitatus redistributed dropped seeds preferentially in bare soil and low sparse vegetation habitats, while M. barbarus redistributed seeds mainly in the high vegetation habitat. These results show that the foraging systems of these harvesting ants determine different patterns of seed removal and dispersal and, thus, affect the abundance and redistribution of seeds in the area.     

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.     

Trail pheromones of ants

Abstract The study of trail laying, recruitment of workers and trail‐following by worker ants comprises a co‐operative study of entomologists and chemists that has resulted in the identification of the chemical nature of such pheromones in many species of five subfamilies of ants. These pheromones may comprise a single compound or, in one exceptional case, a blend of as many as 14 compounds, they may come from a single gland, or in some cases, a combination of two glands. They may be peculiar to a single species or may be shared by a number of species. They exist in the glandular secretion in nanogram to picogram quantities and are detected by workers in minute amounts on a trail. The present state of knowledge of these pheromones and their chemical structures is reviewed. Suitable bioassays and odour perception are discussed and the stereobiology of a few examples is considered.     

Worker size variation and the evolution of an ant-plant mutualism: Comparative morphometrics of workers of two closely related plant-ants, Petalomyrmex phylax and Aphomomyrmex afer (Formicinae)

Summary: We compared intranidal variation in worker size in the two closely related plant-ants Aphomomyrmex afer and Petalomyrmex phylax. Each of these genera is monotypic, and the two appear to be sister species among extant ants. Workers of A. afer are larger on average and exhibit much greater intranidal size variation. Workers of P. phylax are smaller and much less variable in size. Both species show weak allometry for some pairs of characters. Head shape is also different in workers of the two species. We discuss these differences in relation to the ecology of A. afer and P. phylax, and propose a scenario for the evolutionary divergence of worker morphology in these two species. Based on comparisons of these two monotypic genera with related ants, we suggest that reduced intranidal variation in worker size is a derived trait in Petalomyrmex.     

How patrollers set foraging direction in harvester ants

Recruitment to food or nest sites is well known in ants; the recruiting ants lay a chemical trail that other ants follow to the target site, or they walk with other ants to the target site. Here we report that a different process determines foraging direction in the harvester ant Pogonomyrmex barbatus. Each day, the colony chooses from among up to eight distinct foraging trails; colonies use different trails on different days. Here we show that the patrollers regulate the direction taken by foragers each day by depositing Dufour's secretions onto a sector of the nest mound about 20 cm long and leading to the beginning of a foraging trail. The patrollers do not recruit foragers all the way to food sources, which may be up to 20 m away. Fewer foragers traveled along a trail if patrollers had no access to the sector of the nest mound leading to that trail. Adding Dufour's gland extract to patroller-free sectors of the nest mound rescued foraging in that direction, while poison gland extract did not. We also found that in the absence of patrollers, most foragers used the direction they had used on the previous day. Thus, the colony's 30-50 patrollers act as gatekeepers for thousands of foragers and choose a foraging direction, but they do not recruit and lead foragers all the way to a food source.     

Foraging Area Marking in Two Related Tetramorium Ant Species (Hymenoptera: Formicidae)

The related ants Tetramorium caespitum and T. impurum mark their foraging area in a species-specific, home range and short-lasting manner. Indeed, ants reaching a new area have a slow linear speed which increases during the marking. Conspecific ants are arrested and attracted by marked areas, while heterospecific ants are reluctant to visit them. However, when the latter do visit marked areas, they move more quickly and less sinuously than conspecific ants and do not stay on the areas. The marking is performed in about 3 min by T. caespitum and in 3 to 6 min by T. impurum. If not reinforced, the marking vanishes in the same time intervals. Neither poison gland nor last sternite extracts reproduce the activity of naturally marked areas, whereas a Dufour gland extract does exactly that. Foraging ants touch the ground with the tip of their gaster. Consequently, we can postulate that the workers mark their foraging area with the contents of this gland, which is associated with the sting apparatus, and that they deposit with the extremity of the gaster. Alien conspecific ants are seldom aggressive to one another, even on marked areas. When encountering each other on unmarked areas, heterospecific ants present some aggressive reactions. On marked areas, their aggressiveness is enhanced and intruder ants are restless, while resident ones walk freely. On ground marked by T. impurum, ants of this species are more aggressive than antagonistic T. caespitum workers. The marking of foraging areas thus induces defense against heterospecifics but not against conspecific ants.     

Chemical interference competition by Monomorium minimum (Hymenoptera: Formicidae)

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

Group hunting in a ponerine ant,Leptogenys nitida Smith

Field observations on the emigration and foraging behaviours of the southern African ponerine ant, Leptogenys nitida, were undertaken at Mtunzini, Natal, South Africa. These colonies have a single ergatoid queen and 200–1000 workers. The nest sites are found in the leaf litter and these nests are moved frequently over distances ranging from 0.5 to 5 m. Leptogenys nitida is a diurnal predator of arthropods dwelling in the leaf litter. Up to 500 workers participate in each foraging trail, and are not led by definite scouts. Ants form clear trunk trails and fan out at various intervals to search for prey. The prey is searched for and retrieved cooperatively. From laboratory tests it was determined that ants will follow pygidial gland extracts, with the poison gland extract eliciting a limited response. The type of army ant behaviour observed in L. nitida seems to be different to that observed in other ponerine ants.     

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.     

Diversity and morphology of abdominal glands in workers of the ant genus Myopias (Formicidae,Ponerinae)

Histological examination of serial sections through the abdomen of workers of three species of Myopias ants revealed the presence of several exocrine glands. These include the common venom and Dufour glands as well as the pygidial gland, but also more specific sternal glands and glands associated with the sting base and the gonostyli. Two of these glands have not been reported previously among ants: one is the paired oblong plate gland, that occurs next to the oblong plate and may have a pheromonal function. The other novel gland is the paired sting shaft gland, that occurs at the dorsal side in the proximal region of the sting shaft. A remarkable characteristic of these Myopias ants is that all glands of class-3 show ducts with gradually widening internal diameter. Myopias emeryi shows a clearly more simple variety of abdominal glands than Myopias maligna and M. sp.1.     

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

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

Task-specific expression of the foraging gene in harvester ants

In social insects, groups of workers perform various tasks such as brood care and foraging. Transitions in workers from one task to another are important in the organization and ecological success of colonies. Regulation of genetic pathways can lead to plasticity in social insect task behaviour. The colony organization of advanced eusocial insects evolved independently in ants, bees, and wasps and it is not known whether the genetic mechanisms that influence behavioural plasticity are conserved across species. Here we show that a gene associated with foraging behaviour is conserved across social insect species, but the expression patterns of this gene are not. We cloned the red harvester ant (Pogonomyrmex barbatus) ortholog (Pbfor) to foraging, one of few genes implicated in social organization, and found that foraging behaviour in harvester ants is associated with the expression of this gene; young (callow) worker brains have significantly higher levels of Pbfor mRNA than foragers. Levels of Pbfor mRNA in other worker task groups vary among harvester ant colonies. However, foragers always have the lowest expression levels compared to other task groups. The association between foraging behaviour and the foraging gene is conserved across social insects but ants and bees have an inverse relationship between foraging expression and behaviour.     

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.     

Semi-claustral colony founding in the seed-harvester ant Pogonomyrmex californicus: a comparative analysis of colony founding strategies

The evolution of queens that rear their first brood solely using body reserves, i.e. fully claustral, is viewed as a major advance for higher ants because it eliminated the need for queens to leave the nest to forage. In an apparently unusual secondary modification, the seed-harvester ant Pogonomyrmex californicus displays obligate queen foraging, i.e. queens must forage to garner the resources necessary to survive and successfully rear their first brood. I examined the potential benefits of queen foraging by comparing ecological and physiological traits between P. californicus and several congeners in which the queen can rear brood using only body reserves. The primary advantage of foraging appears to lie in providing the queens of P. californicus with the energy to raise significantly more brood than possible by congeners that use only body reserves; the workers reared in the first brood were also heavier in mass than that predicted by their head width. Other correlates of queen foraging in P. californicus relative to tested congeners included a significantly lower total fat content for alate queens, a small queen body size, and a low queen to worker body mass ratio. Queens also forage in several other well-studied species of Pogonomyrmex, suggesting the possibility that queen foraging may be more common than previously thought in higher ants.