Isolation, identification, synthesis and biological activity of volatile compounds from the heads of Atta ants

S-(+)-4-methyl-3-heptanone has been identified as the principal alarm pheromone of Atta texana and Atta cephalotes. Both enantiomers of 4-methyl-3-heptanone have been synthesized and their biological activities have been compared on both species of ants. Comparison of the geometric averages of response ratios, at threshold concentration levels on A. texana, showed S-(+)-4-methyl-3-heptanone to be about 100 times more active than the (?) enantiomer. A similar analysis also showed no inhibition of the activity of S-(+)-4-methyl-3-heptanone by the (?) enantiomer. A less rigorous study on A. cephalotes showed S-(+)-4-methyl-3-heptanone to be about 210 times more active than R-(?)-4-methyl-3-heptanone.Both ant species produce 3-octanone, possible trace amounts of 3-octanol, and both diastereomers of 4-methyl-3-heptanol. A. texana also produces (+)-2-heptanol, 2-heptanone, and 3-heptanol. A. cephalotes contains trace amounts of 2-heptanone.     

Ant-repellent sesquiterpene lactones from Eupatorium quadrangularae

The chloroform extract from the leaves of Eupatorium quadrangularae has been systematically fractionated by following biological activity in a bioassay which measures repellency to the leafcutter ant Atta cephalotes (Formicidae, Attini). Several sesquiterpene lactones were isolated, two of which showed significant ant-repellency.     

Ant-repellent terpenoids from Melampodium divaricatum

The leaves of Melampodium divaricatum have been systematically fractionated by following biological activity in an assay which measures repellency to the leafcutter ant Atta cephalotes (Formicidae, Attini). Several terpenoids have been isolated which show significant ant-repellency.     

An integumentary pheromone-secreting gland in Atta sp: Territorial marking with a colonyspecific pheromone in Atta cephalotes

Workers of Atta cephalotes mark the area around their nest with a pheromone that has at least two components, one of which is colony-specific. Another, which was isolated and tested for its activity, is genus- or species-specific in its action; it appears to be similar in A. sexdens and A. cephalotes, but differs in Acromyrmex octospinosus. The pheromone is produced in a newly described gland, located near the sting. A synthetic trail pheromone component in very low concentrations stimulates some behavioural effects similar to those of the territorial pheromone.     

Sodium‐specific foraging by leafcutter ant workers (Atta cephalotes,Hymenoptera: Formicidae)

1. Sodium is often a limiting nutrient for terrestrial animals, and may be especially sought by herbivores. Leafcutter ants are dominant herbivores in the Neotropics, and leafcutter foraging may be affected by nutritional demands of the colony and/or the demands of their symbiotic fungal mutualists. We hypothesized that leafcutter colonies are sodium limited, and that leafcutter ants will therefore forage specifically for sodium. 2. Previous studies demonstrated that leafcutter Atta cephalotes Linnaeus workers preferentially cut and remove paper baits treated with NaCl relative to water control baits. Atta cephalotes colonies in this study were presented with baits offering NaCl, Na₂SO₄, and KCl to test whether leafcutters forage specifically for sodium. Sucrose and water were used as positive and negative controls, respectively. 3. Atta foragers removed significantly more of the baits treated with NaCl and Na₂SO₄ than the KCl treatment, which did not differ from water. The NaCl and Na₂SO₄ treatments were collected at similar rates. We conclude A. cephalotes forage specifically for sodium rather than for anions (chloride) or solutes in general. This study supports the hypothesis that leafcutter ants are limited by, and preferentially forage for, sodium.     

Effects of pasture and forest microclimatic conditions on the foraging activity of leaf-cutting ants

The fragmentation and transformation of land cover modify the microclimate of ecosystems. These changes have the potential to modify the foraging activity of animals, but few studies have examined this topic. In this study, we investigated whether and how the foraging activity of the leaf-cutter ant Atta cephalotes is modified by microclimatic variations due to land cover change from forest to pasture. We characterized the microclimate of each habitat and identified alterations in foraging behavior in response to relative humidity (RH), air temperature, and surface temperature along ant foraging trails by synchronously assessing foraging activity (number of ants per 5 min including incoming laden and unladen and outgoing ants) and microclimatic variables (air temperature, RH, and maximum and minimum surface temperature along the foraging trail). There were climatic differences between habitats during the day but not throughout the night, and A. cephalotes was found to have a high tolerance for foraging under severe microclimatic changes. This species can forage at surface temperatures between 17 and 45°C, air temperatures between 20 and 36°C, and an RH between 40% and 100%. We found a positive effect of temperature on the foraging activity of A. cephalotes in the pasture, where the species displayed thermophilic behavior and the ability to forage across a wide range of temperatures and RH. These results provide a mechanism to partially explain why A. cephalotes becomes highly prolific as anthropogenic disturbances increase and why it has turned into a key player of human-modified neotropical landscapes.     

Some factors affecting the site and pattern of leaf-cutting activity in the ant Atta cephalotes L.

An account is given of some aspects of the leaf-cutting behaviour of the ant Atta cephalotes L. Chemical and physical factors that determine the site of cutting are described, and the significance of these in the pattern of plant attack is discussed.     

Epiphyll deterrence to the leafcutter ant Atta cephalotes

Summary Epiphyll growth on leaves of the grapefruit Citrus paradisi and the understory cyclanth Cyclanthus bipartitus repelled the fungus-growing, leafcutter ant Atta cephalotes from harvesting leaves of these tropical plants. Experimental removal of epiphylls from leaves resulted in 2–3 times more herbivore damage by leafcutter ants as compared to matched leaves with epiphylls. Because of the protection from herbivore damage, host plants may derive a partial fitness benefit from association with epiphylls.     

The Importance of Where to Dump the Refuse: Seed Banks and Fine Roots in Nests of the Leaf‐Cutting Ants Atta cephalotes and A. colombica1

The location of the nutrient‐rich organic refuse produced by a leaf‐cutting ant colony varies among ant species. Atta cephalotes locate their organic refuse in subterranean chambers, whereas A. colombica place their organic refuse on the soil surface near the nest. We studied the effect of the absence or presence of external organic refuse on the abundance of fine roots and seed bank composition in the superficial horizons of ant nests. We sampled soils from ant nests or dumps and adjacent areas of 15 adult nests of A. cephalotes at La Selva (LS), Costa Rica, and of 15 of A. colombica nests on Barro Colorado Island (BCI), Panama. Soils from A. cephalotes nests did not differ from adjacent soils in abundance of fine‐root and seed diversity. In contrast, organic refuse from A. colombica nests was less diverse in seed composition (due to the great abundance of Miconia argentea) and had a greater abundance of fine roots than adjacent areas. Thus the external location of the ant‐nest organic refuse is potentially important in determining the different types of plant recolonization in abandoned or dead ant nests. The relative abundance of these Atta species may influence the structure and/or composition of tropical forests.     

Enrichment and Broad Representation of Plant Biomass-Degrading Enzymes in the Specialized Hyphal Swellings of Leucoagaricus gongylophorus,the Fungal Symbiont of Leaf-Cutter Ants

Leaf-cutter ants are prolific and conspicuous constituents of Neotropical ecosystems that derive energy from specialized fungus gardens they cultivate using prodigious amounts of foliar biomass. The basidiomycetous cultivar of the ants, Leucoagaricus gongylophorus, produces specialized hyphal swellings called gongylidia that serve as the primary food source of ant colonies. Gongylidia also contain plant biomass-degrading enzymes that become concentrated in ant digestive tracts and are deposited within fecal droplets onto fresh foliar material as ants incorporate it into the fungus garden. Although the enzymes concentrated by L. gongylophorus within gongylidia are thought to be critical to the initial degradation of plant biomass, only a few enzymes present in these hyphal swellings have been identified. Here we use proteomic methods to identify proteins present in the gongylidia of three Atta cephalotes colonies. Our results demonstrate that a diverse but consistent set of enzymes is present in gongylidia, including numerous plant biomass-degrading enzymes likely involved in the degradation of polysaccharides, plant toxins, and proteins. Overall, gongylidia contained over three quarters of all biomass-degrading enzymes identified in the L. gongylophorus genome, demonstrating that the majority of the enzymes produced by this fungus for biomass breakdown are ingested by the ants. We also identify a set of 40 of these enzymes enriched in gongylidia compared to whole fungus garden samples, suggesting that certain enzymes may be particularly important in the initial degradation of foliar material. Our work sheds light on the complex interplay between leaf-cutter ants and their fungal symbiont that allows for the host insects to occupy an herbivorous niche by indirectly deriving energy from plant biomass.     

In vitro evaluation of Trichoderma and Gliocladium antagonism against the symbiotic fungus of the leaf-cutting ant Atta cephalotes

The antagonistic activity of Trichoderma and Gliocladium isolates against Attamyces sp., a symbiotic fungus of the leaf-cutting ant Atta cephalotes, was investigated. A. cephalotes cultures this fungus as the primary food source. Most of the Trichodema and Gliocladium isolates tested in vitro (82.6%) inhibited the Attamyces sp. mycelial growth, which was probably due to their colonization ability and competition for nutrients, both of them known mechanisms of some species of these genera. T. lignorum strain T-26 was the strongest inhibitor achieving a colonization of 23%. Microscopical observations indicate that the inhibitory effect was caused by an interaction that took place in close contact with the host hypha, causing wall deformation that led to the collapse of the turgor pressure. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ontogenetic changes in forager polymorphism and foraging ecology in the leaf-cutting ant Atta cephalotes

In the leaf-cutting ant Atta cephalotes (L.) small colonies produce a relatively narrow size-range of small workers, whereas large colonies produce a much wider size-range of workers. In this study, I compared the foraging of four small A. cephalotes colonies (fewer than 5000 workers) with published data on foraging of large colonies to examine how colony size and worker size-range may be related to foraging ecology in leaf-cutting ants. I found that the foraging ecology of small A. cephalotes colonies is very different from that of large colonies. In small colonies, a relatively narrow size-range of foragers (1.4–6.7 mg, mean 3.3 mg) cut primarily herbs (ferns, grasses, and other small herbaceous plants) located within 7 m of the nest. In contrast, in large colonies, a broader size-range of workers (1.4–30 mg, mean 7.3 mg) participate in foraging, generally harvesting from trees 20–80 m from the nest, with larger workers cutting on trees with thicker and tougher leaves. Small colonies' dependence on small herbaceous plants near the nest may have a profound impact on distribution of A. cephalotes. A. cephalotes colonies are rarely found in primary forest, where the low occurrence of small herbaceous plants in the understory may preclude the establishment of young colonies.     

Ants Do Not Traverse the Silk of Adult Female <Emphasis Type="Italic">Nephila clavipes</Emphasis> (Linnaeus) Webs

Many organisms use chemicals to deter enemies. Some spiders can modify the composition of their silk to deter predators from climbing onto their webs. The Malaysian golden orb-weaver Nephila antipodiana (Walckenaer) produces silk containing an alkaloid (2-pyrrolidinone) that functions as a defense against ant invasion—ants avoid silk containing this chemical. In the present study, we test the generality of ants’ silk avoidance behavior in the field. We introduced three ant species to the orb webs of Nephila clavipes (Linnaeus) in the tropical rainforest of La Selva, Costa Rica. We found that predatory army ants (Eciton burchellii Westwood) as well as non-predatory leaf-cutting ants (Atta cephalotes Linnaeus and Acromyrmex volcanus Wheeler) avoided adult N. clavipes silk, suggesting that an additional species within genus Nephila may possess ant-deterring silk. Our field assay also suggests that silk avoidance behavior is found in multiple ant species.     

Forager size and ecology of Acromyrmex coronatus and other leaf-cutting ants in Costa Rica

I compare forager size and foraging ecology of the leaf-cutting ant Acromyrmex coronatus (Fabricius) with published data on three other leaf-cutter species in Costa Rica, Atta cephalotes (L.), Acromyrmex octospinosus (Reich), and Acromyrmex volcanus Wheeler. Intra-and interspecific differences in forager size in these leaf-cutting ants appear to reflect the economics of harvesting different preferred resources. Ac. coronatus colonies have relatively small foragers (mean mass=3.4±1.4 mg) that cut almost exclusively the thin, soft leaves and other parts of small herbaceous plants. Similarly, small A. cephalotes colonies have small foragers (3.3±1.0 mg) that attack the leaves of small herbaceous plants. In contrast, mature A. cephalotes colonies have a wider sizerange of foragers (7.3±4.1 mg) that primarily attack the leaves of trees, with larger foragers cutting thicker, tougher leaves. In A. cephalotes, the match of forager size to leaf type (both ontogenetically and behaviorally) increases foraging efficiency. Extreme forager polymorphism in mature A. cephalotes colonies appears to broaden the diversity of tree species that they can exploit efficiently. Ac. octospinosus and Ac. volcanus both have large, relatively monomorphic foragers (13.3±4.2 mg and 30.6±4.3 mg, respectively) that typically scavenge for pieces of fallen vegetation, such as dead leaves, fruit, and flowers, in addition to cutting herbs. The large foragers of Ac. octospinosus and Ac. volcanus appear to be well suited as generalist foragers, able to cut or collect any desirable vegetation encountered. Ac. coronatus is similar to A. cephalotes in other ways. Both Ac. coronatus and A. cephalotes establish and maintain cleared trunk trails for foraging, and both have minima workers that hitchhike on the loads carried by foragers, apparently serving to protect the larger foragers from attack by phorid flies. Trunk trails and hitchhikers are not known for Ac. octospinosus and Ac. volcanus. That A. coronatus and A. cephalotes show little overlap in geographic distribution within Costa Rica may relate both to differences in habitat requirements and to interspecific competition.     

Leaf cutter ants (Atta cephalotes) harvest baits offering sodium chloride rewards

Recent studies of attraction to sodium chloride baits suggest that diverse ant species forage for salt. We used experimental presentations of salt baits to test whether leaf cutter ants (Atta cephalotes) are attracted to and harvest salt-treated paper baits that offer no other resources. Atta foragers were most attracted to sucrose baits (positive control), but more foragers touched and cut salt-treated baits than water-treated baits (negative control). Furthermore, the ants removed more paper from the salt baits than from water-treated baits. We conclude that leaf cutter ants expend time and energy to harvest salt in the absence of other rewards. Salt could be harvested for the workers’ consumption, or it could be fed to the fungus gardens in the ants’ nest.     

Comparative analysis of DNA extraction methods to study the body surface microbiota of insects: A case study with ant cuticular bacteria

High‐throughput sequencing of the 16S rRNA gene has considerably helped revealing the essential role of bacteria living on insect cuticles in the ecophysiology and behaviour of their hosts. However, our understanding of host‐cuticular microbiota feedbacks remains hampered by the difficulties of working with low bacterial DNA quantities as with individual insect cuticle samples, which are more prone to molecular biases and contaminations. Herein, we conducted a methodological benchmark on the cuticular bacterial loads retrieved from two Neotropical ant species of different body size and ecology: Atta cephalotes (~15 mm) and Pseudomyrmex penetrator (~5 mm). We evaluated the richness and composition of the cuticular microbiota, as well as the amount of biases and contamination produced by four DNA extraction protocols. We also addressed how bacterial community characteristics would be affected by the number of individuals or individual body size used for DNA extraction. Most extraction methods yielded similar results in terms of bacterial diversity and composition for A. cephalotes (~15 mm). In contrast, greater amounts of artefactual sequences and contaminations, as well as noticeable differences in bacterial community characteristics were observed between extraction methods for P. penetrator (~5 mm). We also found that large (~15 mm) and small (~5 mm) A. cephalotes individuals harbour different bacterial communities. Our benchmark suggests that cuticular microbiota of single individual insects can be reliably retrieved provided that blank controls, appropriate data cleaning, and individual body size and functional role within insect society are considered in the experiment.     

Leucoagaricus gongylophorus Produces Diverse Enzymes for the Degradation of Recalcitrant Plant Polymers in Leaf-Cutter Ant Fungus Gardens

Plants represent a large reservoir of organic carbon comprised primarily of recalcitrant polymers that most metazoans are unable to deconstruct. Many herbivores gain access to nutrients in this material indirectly by associating with microbial symbionts, and leaf-cutter ants are a paradigmatic example. These ants use fresh foliar biomass as manure to cultivate gardens composed primarily of Leucoagaricus gongylophorus, a basidiomycetous fungus that produces specialized hyphal swellings that serve as a food source for the host ant colony. Although leaf-cutter ants are conspicuous herbivores that contribute substantially to carbon turnover in Neotropical ecosystems, the process through which plant biomass is degraded in their fungus gardens is not well understood. Here we present the first draft genome of L. gongylophorus, and, using genomic and metaproteomic tools, we investigate its role in lignocellulose degradation in the gardens of both Atta cephalotes and Acromyrmex echinatior leaf-cutter ants. We show that L. gongylophorus produces a diversity of lignocellulases in ant gardens and is likely the primary driver of plant biomass degradation in these ecosystems. We also show that this fungus produces distinct sets of lignocellulases throughout the different stages of biomass degradation, including numerous cellulases and laccases that likely play an important role in lignocellulose degradation. Our study provides a detailed analysis of plant biomass degradation in leaf-cutter ant fungus gardens and insight into the enzymes underlying the symbiosis between these dominant herbivores and their obligate fungal cultivar.     

Comparative effectiveness of wild bee pollination on the post-harvest characteristics of Grewia asiatica (Malvaceae)

Measuring the pollination potential of different native bees is helpful in identifying the most efficient species for their conservation and proper utilization. The current study was carried out at the Research Farm of The Islamia University of Bahawalpur to compare the pollination efficiency of four native bee species: Apis dorsata, Megachile bicolor, M. cephalotes and Megachile (Callomegachile) sp. Apis dorsata was the most abundant floral visitor of Grewia asiatica comprising 36.46% of floral visitors following by M. cephalotes and Megachile sp. The peak abundance of A. dorsata and M. bicolor was recorded at 12:00 and 08:00, respectively whereas for M. cephalotes and Megachile sp. at 16:00. Visitation frequency, stay time, body and proboscis length were significantly higher in A. dorsata whereas visitation rate, pollen load and pollen deposition were significantly higher in M. bicolor. The maximum fruit weight was recorded when M. bicolor and Megachile sp. had been the pollinators. The post-harvest fruit weight loss was lower in M. bicolor pollinated fruit -with more gradual wrinkling- than in fruit that had resulted from pollination by A. dorsata, M. cephalotes and Megachile sp. Our results suggest that M. bicolor was better pollinator of G. asiatica in terms of its reproductive success and post-harvest qualities. Further studies should focus on conservation of M. bicolor in the region.     

Corrigendum: Shear adhesive performance of leaf-cutting ant workers (Atta cephalotes)

In our previous article, Shear adhesive performance of leaf-cutting ant workers (Atta cephalotes), a technical error occurred when calculating shear adhesive performance divided by tarsal pad area of worker ants carrying leaves (Stark, A. Y., Davis, H. R., & Harrison, W. K. (2019). Biotropica, 51(4), 572–580). Shear adhesive performance of worker ants carrying leaves was mistakenly divided by the tarsal pad area of workers riding on leaves. This has slightly changed our results. After correcting for this error, there is now no statistically significant difference in shear adhesive performance divided by tarsal pad area of worker ants riding on leaves and those carrying leaves. Shear adhesive performance of these groups remains statistically different than soldiers, and our original results (shear adhesive performance of all three groups differ from one another) are consistent with the reported trend in the original article using true pad area for each individual (rather than estimated). We list below the pages and figures in the original article that this correction applies to. All authors agree with this change, apologize for their error, and appreciate the opportunity granted by the editors and publisher to make this correction. Our original conclusion, that there is variation in shear adhesive performance per unit area among worker roles of Atta cephalotes, is still supported by these corrected results.     

Head-on encounter rates and walking speed of foragers in leaf-cutting ant traffic

Summary. Trail traffic of the leaf-cutting ant Atta cephalotes involves intermingled flows of outbound and returning foragers. Head-on encounters between workers from the opposite flows are a common occurrence in this traffic. Each encounter momentarily delays the two ants involved, and these small delays might pose a significant cost to the colony's foraging performance when summed over thousands of workers along many metres of trail. We videotaped outbound and returning foragers over a 1 m course, and measured the encounter rates they experienced and their velocity. Our analysis indicates that locomotion speed is diminished by increasing encounter rate, but that the effect is small relative to the effects of ant body size and load mass. Head-on encounters allow exchange of information and leaf fragments between workers, and we consider how the benefits of such encounters may make this form of traffic organization superior to segregated outbound and returning lanes, despite the measurable c ost of encounters in mixed traffic.