Leaf-cutting Ants Research Articles

Genomic Signatures of Domestication in a Fungus Obligately Farmed by Leafcutter Ants.

The naturally selected fungal crop (Leucoagaricus gongylophorus) farmed by leafcutter ants shows striking parallels with artificially selected plant crops domesticated by humans (e.g. polyploidy, engorged nutritional rewards, and dependence on cultivation). To date, poorly resolved L. gongylophorus genome assemblies based on short-read sequencing have constrained hypotheses about how millions of years under cultivation by ants shaped the fungal crop genome and potentially drove domestication. We use PacBio HiFi sequencing of L. gongylophorus from the leafcutter ant Atta colombica to identify 18 putatively novel biosynthetic gene clusters that likely cemented life as a cultivar (e.g. plant fragment degradation, ant-farmer communication, and antimicrobial defense). Comparative analyses with cultivated and free-living fungi showed genomic signatures of stepwise domestication transitions: (i) free-living to ant-cultivated: loss of genes conferring stress response and detoxification; (ii) hyphal food to engorged nutritional rewards: expansions of genes governing cellular homeostasis, carbohydrate metabolism, and siderophore biosynthesis; and (iii) detrital provisioning to freshly cut plant fragments: gene expansions promoting cell wall biosynthesis, fatty acid metabolism, and DNA repair. Comparisons across L. gongylophorus fungi farmed by 3 leafcutter ant species highlight genomic signatures of exclusively vertical clonal propagation and widespread transposable element activity. These results show how natural selection can shape domesticated cultivar genomes toward long-term ecological resilience of farming systems that have thrived across millennia.

Two +ssRNA mycoviruses cohabiting the fungal cultivar of leafcutter ants

Leafcutter ants are dominant herbivores in the Neotropics and rely on a fungus (Leucoagaricus gongylophorus) to transform freshly gathered leaves into a source of nourishment rather than consuming the vegetation directly. Here we report two virus-like particles that were isolated from L. gongylophorus and observed using transmission electron microscopy. RNA sequencing identified two +ssRNA mycovirus strains, Leucoagaricus gongylophorus tymo-like virus 1 (LgTlV1) and Leucoagaricus gongylophorus magoulivirus 1 (LgMV1). Genome annotation of LgTlV1 (7401 nt) showed conserved domains for methyltransferase, endopeptidase, viral RNA helicase, and RNA-dependent RNA polymerase (RdRp). The smaller genome of LgMV1 (2636 nt) contains one open reading frame encoding an RdRp. While we hypothesize these mycoviruses function as symbionts in leafcutter farming systems, further study will be needed to test whether they are mutualists, commensals, or parasites.

Genome Mining for Diazo-Synthesis-Related Genes in Streptomyces sp. CS057 Unveiled the Cryptic Biosynthetic Gene Cluster crx for the Novel 3,4-AHBA-Derived Compound Crexazone 2.

Natural products play a crucial role in drug development, addressing the escalating microbial resistance to antibiotics and the treatment of emerging diseases. Progress in genome sequencing techniques, coupled with the development of bioinformatics tools and the exploration of uncharted habitats, has highlighted the biosynthetic potential of actinomycetes. By in silico screening for diazo-related gene genomes from twelve Streptomyces strains isolated from Attini leaf-cutting ants, the new crx biosynthetic gene cluster (BGC) was identified in Streptomyces sp. CS057. This cluster, highly conserved in several Streptomyces strains, contains genes related to diazo group formation and genes for the biosynthesis of 3,4-AHBA. By overexpressing the LuxR-like regulatory gene crxR1, we were able to activate the crx cluster, which encodes the biosynthesis of three 3,4-AHBA-derived compounds that we named crexazones (CRXs). The chemical structure of crexazones (CRXs) was determined by LC-DAD-HRMS-based dereplication and NMR spectroscopic analyses and was found to correspond to two known compounds, 3-acetamido-4-hydroxybenzoic acid (CRX1) and the phenoxazinone texazone (CRX3), and a novel 3,4-AHBA-containing compound herein designated as CRX2. Experimental proof linking the crx BGC to their encoded compounds was achieved by generating mutants in selected crx genes.

Leaf-cutting ants’ distribution in an elevation gradient in central Argentina

ABSTRACT Leaf-cutting ants are among the most prominent herbivores in neotropical forests and savannas, and Argentina represents the southern limit of their distribution. Despite their importance, few systematic studies analyze the presence and distribution of leaf-cutting ants in Argentina. Our aim was to describe, through an intensive field sampling, the leaf-cutting ant species present in the central Argentine mountains and analyze their distribution along the elevation gradient. We collected ants from 69 nests in 56 out of the 250 plots visited along the study elevation gradient (400–2700 m above sea level) in seven different habitats, from forests to rocky areas. We found six species. The most frequent were Acromyrmex lobicornis and Acromyrmex crassispinus, while Acromyrmex heyeri, Amoimyrmex silvestrii, Amoimyrmex striatus, and Amoimyrmex bruchi were far less frequent. The species distributed at the highest elevation was A. lobicornis (1223 to 2163 m a.s.l.), showing significant differences with the other species. We found leaf-cutting ants in all habitats, with a higher presence in grazing lawns, shrublands, and exotic forests. Our results indicate that leaf-cutting ants are present in most of the mountain range, as the area above their upper limit of distribution represents less than 5% of the total mountain area.

Harmony under threat: does resource-mediated stress affect the (caste-based) social network of leaf-cutting ant colonies?

Managing pest species of eusocial insects, such as leaf-cutting ants, poses significant challenges. Controlling them requires understanding of how toxic plant substrates and ant baits are recognized by foragers, transported to the nest, shared among workers and managed by gardeners cultivating the symbiont fungus garden. Despite this, little is known about how unsuitable resources might impact social interactions within ant colonies. This study aims to investigate whether the provision of a suitable substrate (copperleaf) and a toxic substrate (nasturtium leaves) affects the social network dynamics within colonies of two leaf-cutting ant species: Acromyrmex molestans and Acromyrmex subterraneus. The interactions between castes were recorded and subjected to social network analyses. Initial foraging duration increased for A. subterraneus provided with copperleaf, although no difference was observed for the other species and resource combinations. The social network structure was similar for both species when copperleaf leaves were provided as a substrate. However, notable alterations occurred with nasturtium leaf provision, leading to higher integration of gardeners in interactions and noticeable changes in the generalist worker network centrality, particularly in A. subterraneus. The observed changes in social interactions, particularly in A. subterraneus, suggest that increasing gardener interactions with other castes expedites the movement of the substrate within the colony. This maximizes the potential toxic effect on the colony. © 2024 Society of Chemical Industry.

Chromosome Mapping of Ribosomal DNA Clusters in Four Leaf-cutting Ant Species of the Genus Acromyrmex, with Description of a Triploid Individual in A. laticeps

The increase of cytogenetic data in the leaf-cutting genus Acromyrmex has shown interesting contributions to the evolutionary and taxonomic approaches, including the creation of a new genus and the description of chromosomal patterns allowing comparative studies within Acromyrmex as well as between this genus and other similar taxa. The conserved chromosome number in Acromyrmex is a notable feature, with some distinguishable chromosomes among the species. In this study, we describe the diploid karyotype of Acromyrmex laticeps in addition to an individual with all the metaphases triploids, suggesting a triploid individual. To the best of our knowledge, this is the first report of polyploidy in a fungus-growing ant. Furthermore, we mapped 18S ribosomal DNA on the chromosomes of A. laticeps and three other Acromyrmex species. Among them, three species showed the ribosomal DNA cluster pattern observed in other previously studied members of this genus, with a terminal location in the largest subtelocentric pair. Meanwhile, Acromyrmex balzani had these ribosomal DNA clusters in its entire short arm. The role of triploidy in ant evolution has also been discussed. The increase in chromosomal data of leaf-cutting ants may provide significant insights into the evolution of this peculiar ant group.

Nasturtium leaf compounds, diphenyl disulfide and lyral, against Atta sexdens (Hymenoptera: Formicidae) and their symbiotic fungi.

Social insect pests, particularly leaf-cutting ants, present a considerable challenge in terms of control. Leaf-cutting ants are significant agricultural, forestry, and pasture pests, and understanding their behavior and defense mechanisms is essential for managing their colonies effectively. While toxic ant baits are a primary control method, the limited availability of effective insecticides and concerns over their hazardous nature has spurred the search for alternative solutions, particularly natural compounds, which aligns with the goals of forest certification groups. In the light of previous evidence demonstrating the efficacy of nasturtium leaves (Tropaeolum majus L. (Brassicales: Tropaeolaceae)) in suppressing leaf-cutting ant colonies, this study investigates 2 active components of nasturtium leaf extracts: diphenyl disulfide and lyral. We tested their impact on Atta sexdens (L.) (Hymenoptera: Formicidae), the most prevalent leaf-cutter ant species in Brazil, and their symbiotic fungus, Leucoagaricus gongylophorus (Möller) Singer (Agaricales: Agaricaceae). We conducted experiments with increasing concentrations of diphenyl disulfide and lyral, assessing their effects on the symbiotic fungus and on forager workers and gardeners of A. sexdens colonies. Our findings revealed no fungicidal activity, and ant mortality was minimal in both topical and ingestion bioassays with the exception of gardeners topically exposed to diphenyl sulfide. Furthermore, the compounds did not affect leaf ingestion, but diphenyl disulfide did increase interactions among foragers. These results suggest that neither diphenyl disulfide nor lyral are the primary contributors to the suppression of leaf-cutting ant colonies by nasturtium leaves. However, they may enhance the formicidal activity of other compounds present in nasturtium leaves.

Herbivory by Leaf-Cutting Ants: Exploring the Jasmonate Response in Host and Non-Host Plants

Leaf-cutting ants (Formicidae; Atta spp., Acromyrmex spp.) cut off pieces of leaves and other plant tissue and feed it to their symbiotic fungi. As this foraging behavior poses an imminent threat to agriculture, leaf-cutting ants are considered as pests of huge ecologically and economically importance. Consequently, research on leaf-cutting ants focused on their foraging decisions and interactions with their cultivated symbiotic fungi, whereas their effect on the attacked plants, apart from the loss of plant tissue, remains largely unknown. In this study, we investigated the consequences of an attack by leaf-cutting ants and analyzed the plants’ defense responses in comparison to chewing caterpillars and mechanical damage. We found that an attack by leaf-cutting ants induces the production of jasmonates in several host and non-host plant species (Arabidopsis thaliana, Vicia faba, Phaseolus lunatus, Tococa quadrialata). Additionally, we showed in the natural host plant lima bean (P. lunatus) that leaf-cutting ant damage immediately leads to the emission of typical herbivory-induced plant volatiles, including green leaf volatiles and terpenoids. Further data exploration revealed clear differences in the defense-related phytohormone profile in plant species of Neotropical and Eurasian origin. Taken together, we show that leaf-cutting ant infestation and their way of clipping the plants’ tissues induce jasmonate and jasmonates-mediated responses and do not differ from those to mechanical injury or larval feeding.

Leaf-cutting ant species (Hymenoptera: Formicidae, Myrmicinae) in three agrosystems and the attractiveness of a natural bait to Atta laevigata’s biocontrol

Leaf-cutting ant species with economic importance are those of the genera: Atta and Acromyrmex. Natural baits with spores of these entomopathogenic fungi can be used in the biological control of pest species. Therefore, the aims of this research, were: 1) inventory the species of leaf-cutting ants in three agroecosystems; 2) evaluate the attractiveness of the natural bait based on orange peel albedo impregnated with a bioinsecticide; 3) compare the amount of baits carried between the different concentrations of the bioinsecticide, and 4) evaluate the difference in the times spent for the first meeting of the bait and beginning of the loading in the direction of the nest by Atta laevigata, in relation to the concentrations of conidia of the bioinsecticide. Active searches were carried out in the anthills to collect adults (“soldiers”) and identify the species. The evaluations of the natural baits occurred in four adult nests of A. laevigata, being offered 2g of baits per repetition. The position of the treatments was changed at each repetition. We found four species: Atta sexdens, Atta laevigata, Acromyrmex rugosus and Acromyrmex balsani. There was a significant difference between the total amount of loaded and unloaded baits, indicating that leaf-cutter ants were attracted by the baits and ignored the presence of Beauveria bassiana conidia. The time for first contact and start of loading, did not differ significantly between treatments, nor between loaded amounts of different treatments. The bait containing the bioinsecticide is attractive to Atta laevigata workers, regardless of the concentration of conidia.

Polyandry may mitigate the negative impact of reproductive interference among bumblebees in Japan

In social hymenopterans, monandry of the queen is an ancestral trait, and polyandry is a derived trait. Polyandry of the queen is the norm in a limited number of lineages, such as honeybees, leaf-cutting ants, Pogonomyrmex ants, and Vespula wasps, which presumably provide fitness advantages for the whole colony. The queen of the introduced bumblebee, Bombus terrestris, is polyandrous in Japan, whereas it is monandrous in native regions. We hypothesize that polyandry can evolve in a process that avoids the negative impacts of reproductive interference caused by interspecific mating and conducted genetic studies of the invasive species B. terrestris and two native subspecies, Bombus hypocrita sapporoensis and Bombus hypocrita hypocrita, in Japan. Our results revealed that although the native queens of B. hypocrita hypocrita allopatric with B. terrestris were strictly monandrous, the native queens of B. hypocrita sapporoensis sympatric with B. terrestris were polyandrous. These results suggested that the queens of native B. hypocrita sapporoensis do not experience negative impacts on interspecific mating from the invasive B. terrestris. We discuss the possibility that reproductive interference is a driving force in selection for multiple mating through an arms race between sympatric species.

Leafcutter ants enhance microbial drought resilience in tropical forest soil.

We conducted a research campaign in a neotropical rainforest in Costa Rica throughout the drought phase of an El-Nino Southern Oscillation event to determine microbial community dynamics and soil C fluxes. Our study included nests of the leafcutter ant Atta cephalotes, as soil disturbances made by these ecosystem engineers may influence microbial drought response. Drought decreased the diversity of microbes and the abundance of core microbiome taxa, including Verrucomicrobial bacteria and Sordariomycete fungi. Despite initial responses of decreasing diversity and altered composition, 6 months post-drought the microbiomes were similar to pre-drought conditions, demonstrating the resilience of soil microbial communities to drought events. A. cephalotes nests altered fungal composition in the surrounding soil, and reduced both fungal mortality and growth of Acidobacteria post-drought. Drought increased CH4 consumption in soils due to lower soil moisture, and A. cephalotes nests decrease the variability of CH4 emissions in some soil types. CH4 emissions were tracked by the abundance of methanotrophic bacteria and fungal composition. These results characterize the microbiome of tropical soils across both time and space during drought and provide evidence for the importance of leafcutter ant nests in shaping soil microbiomes and enhancing microbial resilience during climatic perturbations.

Isocycloseram: A new active ingredient for leaf-cutting ants control.

Leaf-cutting ants are the most important pests in several cropping systems in the Neotropics. Granulated baits containing active ingredients, considered hazardous by the Stockholm Convention, are the usual method to control these ants. Isocycloseram is a new insecticide molecule with high safety margin for mammals, but without registration for the ants in general. Thus, this study investigated the effectiveness of granulated baits with isocycloseram in leaf-cutting ants control under laboratory and field conditions. Initially, the mortality of Atta sexdens workers, fed with dehydrated citrus pulp paste containing different concentrations of isocycloseram was evaluated in the laboratory for 21 days, for toxicological classification. Subsequently, the loading, devolution, and incorporation of baits with different concentrations of isocycloseram and the mortality of A. sexdens colonies were evaluated in the laboratory. After that, the percentages of loading and devolution of baits, foraging activity, and colony mortality treated with 0.05, 0.1, 0.2, and 0.3% of isocycloseram were evaluated for the species A. sexdens, A. laevigata, and Acromyrmex lundii in field conditions. All concentrations of isocycloseram killed more than 15% of ants in 24 h and more than 90% in 21 days in the laboratory, being classified as a fast-acting and highly effective active ingredient. Baits with 0.001 to 0.03% of isocycloseram were highly loaded and exhibited low rate of devolution. The mortality of A. sexdens colony was higher at concentrations between 0.075 and 0.3%, in the laboratory. Baits containing isocycloseram at concentrations of 0.2 and 0.3% were highly loaded, presented low devolution rates, and were highly efficient in controlling A. sexdens, A. laevigata, and A. lundii in the field, at dosages of 6, 10, and 12 g/m² of nest. This is the first report of the use of isocycloseram against leaf-cutting ants, contributing to the development of efficient and toxicologically safer ant baits.

Battles between ants (Hymenoptera: Formicidae): a review.

With their unique colony structure, competition between ants (Hymenoptera: Formicidae) can be particularly intense, with colonies potentially willing to sacrifice large number of individuals to obtain resources or territory under the right circumstances. In this review, we cover circumstances in which ant competition escalates into combat, battle strategies and tactics, and analysis methods for these battles. The trends for when colonies choose to fight can vary greatly dependent on the species and situation, which we review in detail. Because of their large group sizes, ant conflicts can follow different patterns than many other species, with a variety of specialist adaptations and battle strategies, such as specialized worker classes and the need to rapidly recruit large number of compatriots. These same large group sizes also can make ant fighting amenable to mathematical analysis, particularly in the context of Lanchester's laws that consider how total numbers influence the outcome of a confrontation. Yet, dynamic behavior can often disrupt idealized mathematical predictions in real-world scenarios, even though these can still shed light on the explanations for such behavior. We also systematically cover the literature on battles between groups of ants, presenting several other interesting studies on species with unique colony organization, such as army ants and leafcutter ants.

City of Leafcutter Ants: A Sustainable Society of Millions by Amy Hevron (review)

City of Leafcutter Ants: A Sustainable Society of Millions by Amy Hevron (review)

Insecticidal and fungicidal activity of Cymbopogon citratus (Poaceae) essential oil on Atta sexdens colonies

Leafcutter ants are one of the most destructive and economically important herbivores in both forest and agricultural crops, due to their abundance and wide distribution. The most used method for controlling this pest is still through synthetic formicides, due to their high efficiency. However, essential oils represent an alternative, as they are biodegradable and selective and have a toxic effect on a wide range of organisms, including leafcutter ants. The combination of insecticidal activity of a product and possible fungicidal activity constitutes an effective strategy against these insect pests, since both agents of this mutualistic interaction (both organisms are benefited) are affected, ensuring quicker collapse of the colony. The aim of this study was to evaluate the insecticidal and fungicidal activity of Cymbopogon citratus essential oil applied on Atta sexdens colonies under laboratory conditions. A nebulized spray system with three concentrations (15, 30 and 60%) and a control treatment were used to evaluate the effect of C. citratus on A. sexdens colonies. The C. citratus essential oils showed both insecticidal activity against the leafcutter ants (A. sexdens) and fungicidal activity against their symbiotic fungi. Colonies exposed to this essential oil showed considerable reduction in the weight of fungal mass, and mortality of both the queen and worker ants, which proves to be promising for the development of new insecticides for management of this insect pest.

Biomimetic Ultrasonic Vibrator with Broadband Characteristics Inspired by Leaf-Cutting Ants.

Power ultrasound is widely used in industrial production, medical equipment, aerospace, and other fields. Currently, there are two main types of commonly used power generation devices: piezoelectric ultrasonic transducers and magnetostrictive ultrasonic transducers. However, in certain situations with limited external dimensions, the applications of existing power ultrasound devices are limited. In nature, leaf-cutting ants excite vibrations through their tiny organs. Inspired by the vibratory organs of leaf-cutting ants, a new type of biomimetic ultrasonic vibrator (BUV) comprising a scraper, dentate disc, and fixture system was proposed, fabricated, and tested in this study. The experimental results showed that the BUV could operate in the frequency range of 16.8-19 kHz. Within the working frequency range, the vibration of the BUV was stable and the amplitude of the vibration displacement was greater than 22 µm. The operating frequency band of the BUV was broader than those of the piezoelectric and magnetostrictive ultrasonic transducers. In addition, the BUV can cut soft rubber and pig tissues with sufficient output power and load-carrying capacity. The BUV, as a new type of power ultrasonic excitation device, is expected to be applied in high-power micro operating scenarios, such as minimally invasive surgical instruments.

Las hormigas culonas: entre patrimonio biocultural y plaga (Santander, Colombia)

The study focuses on the consumption of big-bottomed ants (hormigas culonas), Atta laevigata (F. Smith, 1858), in the department of Santander, Colombia. It analyzes the complex interactions between local communities and these insects, which are appreciated as a regional food heritage but are also seen as pests due to the significant damage they cause to crops. It highlights the importance of local knowledge in collecting ants and how their commercialization has experienced a remarkable increase, partly due to the migration of Santander residents and tourism. The article also discusses the ecological importance of leafcutter ants in ecosystems. In addition, it suggests the need for a broader approach to preserve these species, considering their role in nature and exploring strategies for coexistence with other species cataloged as pests. It argues that food heritage can play a crucial role in promoting these approaches.

Soil Fungal Pathogens from Different Land Uses/Covers and Their Virulence to Leaf-Cutter Ant, Atta cephalotes1

Soil Fungal Pathogens from Different Land Uses/Covers and Their Virulence to Leaf-Cutter Ant, Atta cephalotes1

Hymenopteran-specific TRPA channel from the Texas leaf cutter ant (Atta texana) is heat and cold activated and expression correlates with environmental temperature.

Leaf cutting ants of the genus Atta cultivate fungal gardens, carefully modifying environmental conditions to maintain optimal temperature for fungal growth. Antennal nerves from Atta are highly temperature sensitive, but the underlying molecular sensor is unknown. Here, we utilize Atta texana (Texas leaf cutter ant) to investigate the molecular basis of ant temperature sensation and how it might have evolved as the range expanded northeast across Texas from ancestral populations in Mexico. We focus on transient receptor potential (TRP) channel genes, the best characterized temperature sensor proteins in animals. Atta texana antennae express 6 of 13 Hymenopteran TRP channel genes and sequences are under a mix of relaxed and intensified selection. In a behavioral assay, we find A. texana workers prefer 24 °C (range 21-26 °C) for fungal growth. There was no evidence of regulatory evolution across a temperature transect in Texas, but instead Hymenoptera-specific TRPA (HsTRPA) expression highly correlated with ambient temperature. When expressed in vitro, HsTRPA from A. texana is temperature activated with Q10 values exceeding 100 on initial exposure to temperatures above 33 °C. Surprisingly, HsTRPA also appears to be activated by cooling, and therefore to our knowledge, the first non-TRPA1 ortholog to be described with dual heat/cold activation and the first in any invertebrate.

Virulence Bioassay of Entomopathogenic Fungi against Adults of Atta mexicana under Controlled Conditions

Leafcutter ants (Atta spp.) are one of the mos t economically harmful pests in agriculture, considered dominant in the Neotropics and South America. Mature colonies of A. mexicana have a great economic impact on Mexico’s agriculture. Microbial agents in the form of biopesticides are an effective component of integrated pest management (IPM) strategies and may present a better alternative to synthetic insecticides. Among the fungi most used as biological insecticides there are Beauveria bassiana and Metarhizium anisopliae. The objective of this research was to evaluate the effect of the entomopathogenic fungi B. bassiana and M. anisopliae of commercial origin and a native strain of B. bassiana from México (MA-Bb1) on adults of Atta mexicana under controlled conditions. In the bioassay, five formulations and a control group were tested (B. bassiana MA-Bb1, B. bassiana MA-Bb1+ Diatomin®, B. bassiana®, M. anisopliae®, Diatomin®, and Tween 80 (0.01%). The MA-Bb1+ Diatomin® biopreparation induced the highest mortality (100%) in four-week-old A. mexicana, followed by the MA-Bb1, M. anisopliae®, and B. bassiana® biopreparations, which caused mortality of 83.33%, 73.98%, and 68.70%, respectively. Treatments containing B. bassiana and M. anisopliae were efficient in controlling A. mexicana under controlled conditions. The most efficient biological control was achieved with the B. bassiana fungus and Diatomin®, which presented the highest total death rate in A. mexicana 96 h post infection, in contrast to the control group (Tween 80), which attained the lowest speed of death in the present investigation.