Leaf-cutting Ants Research Articles

Does resource-mediated stress affect colony personality in leaf-cutting ants?

Animal personality refers to behavioral consistency and propensity. In social insects, little is known about the interplay between colony personality and colony foraging. This study aimed to assess personality traits among colonies of the leaf-cutting ants Acromyrmex subterraneus subterraneus and Acromyrmex subterraneus molestans and examine their behavioral consistency when provided with a toxic substrate, nasturtium leaves [Tropaeolum majus L. (Tropaeolaceae)], with potential as a management tool against these pest species. The association between colony behavioral traits and fungus garden growth was also examined, and thus the efficacy of the colony suppression. Behavioral variation was higher between colonies than between subspecies. Behavioral traits were correlated before and after exposure to resource-mediated stress in both subspecies, indicating the existence of behavioral syndrome. The dimensions that contributed most to colony personality (activity, aggressiveness, and boldness) are directly related to colony resource searching and foraging. However, these dimensions diverged in their contribution before and after exposure to nasturtium. Colony activity was the major determinant of fungus garden growth, which is probably a consequence of its relationship with foraging behaviors and maintenance of the fungus garden. As the personality of a colony is unequally defined by its constituent castes, the relationship and network of interactions are determinants of foraging behaviors with relevant consequences for colony suppression using toxic foraging substrates that impair these relationships and interactions, as nasturtium leaves do. Therefore, it is plausible to say that resource-mediated stress affects colonies personality exhibiting control potential against these species.

Ant nesting ecology of leaf-cutter ants in altitude natural fields, southern Brazil

This work aimed to study the ecological aspects of the nesting process carried out by Atta and Acromyrmex leaf-cutter ants in the Campos de Lages Microregion, Brazil. In each municipality 4 equidistant observation sites were established, each point representing an anthill, for a total of 72 anthills. All cutter anthill’s sampled were georeferenced and measured in relation to their surface. Soil samples were collected at three points at 1.5 m from each anthill, at a depth of 10 to 20 cm. Subsequently, the environmental characterization and definition of the architecture of each anthill were performed. The clay contents influenced the selection process of ant nesting sites of the species Atta ssp., and the Al contents and pH values of the soil influenced the nesting process of Acromyrmex ssp. ants. The Acromyrmex spp. anthills were located at higher altitudes than the Atta ssp. anthills. Regarding Atta ssp. anthill’s have a rough shape, are apparent and preferably located on the edges of vegetative fragments. Acromyrmex spp. anthill’s have a circular shape, are apparent, and preferably located in areas on the edges of forest fragments.

Formicidal activity of essential oils of Myrcia lundiana chemotypes on Acromyrmex balzani

Essential oils (EOs) from plants have been considered as a viable alternative to the use of synthetic insecticides for the control of insect pests. In the current study, we evaluated the formicidal activity of essential oils of two Myrcia lundiana (Myrtaceae) chemotypes, their major compounds and their binaries mixtures on Acromyrmex balzani (Emery, 1980) (Hymenoptera: Formicidae). The effects of essential oils on A. balzani were evaluated by fumigation toxicity bioassays and behavioral tests. The major concentration of isopulegol and citral in the essential oils characterized the two M. lundiana chemotypes, with 1,8-cineol being the second compound with the highest concentration. The essential oils and their major compounds were toxic to A. balzani workers. The isolated isopulegol and citral were around 14 and four times more toxic than the essential oils of their respective chemotypes. The mixture of the major compounds with 1,8-cineol resulted in an antagonistic effect. The treatments provoked rapid mortality and altered the walking behavior of A. balzani. Isopulegol resulted the highest toxicity, while the citral chemotype showed a more persistent repellent effect on A. balzani. The EOs of the M. lundiana chemotypes allow to obtain compounds for the development of new insecticides for the program management of leaf-cutting ants.

Comparative FISH-mapping of TTAGG telomeric sequences to the chromosomes of leafcutter ants (Formicidae, Myrmicinae): is the insect canonical sequence conserved?

Telomeric sequences are conserved across species. The most common sequence reported among insects is (TTAGG)n, but its universal occurrence is not a consensus because other canonical motifs have been reported. In the present study, we used fluorescence in situ hybridization (FISH) using telomeric probes with (TTAGG)6 repeats to describe the telomere composition of leafcutter ants. We performed the molecular cytogenetic characterization of six Acromyrmex Mayr, 1865 and one Atta Fabricius, 1804 species (Acromyrmex ambiguus (Emery, 1888), Ac. crassispinus (Forel, 1909), Ac. lundii (Guérin-Mèneville, 1838), Ac. nigrosetosus (Forel, 1908), Ac. rugosus (Smith, 1858), Ac. subterraneus subterraneus (Forel, 1893), and Atta sexdens (Linnaeus, 1758)) and described it using a karyomorphometric approach on their chromosomes. The diploid chromosome number 2n = 38 was found in all Acromyrmex species, and the karyotypic formulas were as follows: Ac. ambiguus 2K = 14M + 12SM + 8ST + 4A, Ac. crassispinus 2K = 12M + 20SM + 4ST + 2A, Ac. lundii 2K = 10M + 14SM + 10ST + 4A, Ac. nigrosetosus 2K = 12M + 14SM + 10ST + 2A, and Ac. subterraneus subterraneus 2K = 14M + 18SM + 4ST + 2A. The exact karyotypic formula was not established for Ac. rugosus. FISH analyses revealed the telomeric regions in all the chromosomes of the species studied in the present work were marked by the (TTAGG)6 sequence. These results reinforce the premise that Formicidae presents high homology between their genera for the presence of the canonical sequence (TTAGG)n.

Ocorrência de formigas cortadeiras em campos de altitude no sul do Brasil

Remanescentes do ecossistema Campos Altitude são encontrados na microrregião de "Campos de Lages", SC, sul do Brasil. O objetivo deste trabalho foi avaliar e identificar espécies de formigas cortadeiras que ocorrem em Campos de Altitude. O estudo foi realizado entre os meses de Agosto de 2012 e Dezembro de 2013, em 18 municípios da micro-região de "Campos de Lages", Santa Catarina, sul do Brasil. No total, 75 formigueiros de cortadeiras foram localizados, medidos e georreferenciados, apresentando 16 formigueiros pertencentes ao gênero Atta e 59 do gênero Acromyrmex. Amostras de formigas de diferentes castas foram recolhidas de cada formigueiro para identificação adequada. Uma espécie foi identificada no gênero Atta, A. sexdens piriventris e oito no gênero Acromyrmex, A. laticeps, A. heyeri, A. Iundii, A. crassispinus, A. ambiguus, A. aspersus, A. coronatus. As espécies Atta sexdens piriventris, Ac. laticeps e Ac. heyeri foram as mais frequentes. Espécies pertencentes ao gênero Acromyrmex foram localizadas em altitudes acima dos 1000 metros, e tamanho médio de formigueiros de 1,04 ± 0,93 m2. Formigueiros do gênero Atta foram localizados em altitudes de até 850 metros, e apresentaram um tamanho médio 132,75 ± 12,96 m2 de área total de superfície, considerando à área dos olheiros.

High Magnesium Calcite and Disordered Dolomite Growth on Leaf-cutting Ants: Challenges and Implications

High Magnesium Calcite and Disordered Dolomite Growth on Leaf-cutting Ants: Challenges and Implications

INFLUENCIA DEL LATEX COMO REPELENTE EN PLANTAS ANTE HORMIGAS CORTADORAS DE HOJAS

Se realizó un experimento corto y sencillo, cuya pregunta de investigación fue: ¿El látex inhibirá los cortes de hoja por parte de las hormigas? Sobre la base de esa cuestión, surgió la hipótesis que el látex inhibe los cortes de hojas por parte de las hormigas, prediciendo que, si se impregna látex a los bordes de las hojas predilectas por hormigas, entonces las hormigas no cortarán estas hojas. El número de cortes realizados en las hojas sin látex fue significativamente mayor con respecto a los cortes en las hojas con látex. Esto indica que el látex por sí solo resulta ser un inhibidor natural contra la presencia de hormigas cortadoras de hojas.

The agroecology power: how the environmental representation and management of leaf­cutting ants by peasants from Assentamento Dênis Gonçalves can be transformed

The relationship between human beings and leaf-cutting ants is secular and emerged along with the agricultural practices for food production. The environmental representation of peasants about leaf-cutting ants may be related to their country life background, implying directly on the control method used by them to reduce agricultural losses. In this context, it was investigated the relationship between the peasants' socioeconomic profile with their environmental representations about leaf-cutting ants and used control methods. Eighty families from Assentamento Denis Goncalves (Brazilian Landless Workers’ Movement) were interviewed, in order to socioeconomically characterize them and ask if they know the term agroecology, what are leaf-cutting ants, their ecological function and used control method. Two profiles were identified, one composed by older peasants who had never studied, did not know the term agroecology, had a negative conception about leaf-cutting ants and used commercial formicides. The second profile was constituted by peasants with the opposite characteristics of the first. Agroecology concepts and practices seem to have a high potential to change environmental representations about leaf-cutting ants and used control methods in the studied area. By comprehending the leaf-cutting ants’ role in the ecosystem a gradative transition to alternative control methods rather than the commercial ones was observed. This gradual transition enables a better relationship between ADG peasants and leaf-cutting ants. The organic compounds commonly used are clues to the urgent search for a sustainable leaf-cutting ant control method.

Divergence in Bergmann’s clines: elevational variation and heritability of body size in a leaf-cutting ant

The variation in size along elevations has been investigated in various insect species, with contradictory results regarding Bergmann’s or James’ rules. Positive, negative, or hump-shaped patterns have been commonly found, but the sources of variation are generally unknown, because the contribution of genetic and environmental factors is not usually estimated. Social insects offer the opportunity to study the intraspecific variation and heritability of morphological traits due to the ease of finding family groups in the wild. Thus, we aimed to assess the variation in morphological characters of Atta cephalotes and to estimate their heritability as an attempt to understand the sources of variation. We sampled 30 soldiers from five nests at six different elevations in Colombia; soldiers were dissected, and ten morphometric characters were measured. Variation was analysed through nested MANOVA and REML analyses, and heritabilities and co-heritabilities were estimated using a full-sib model. We found significant differences between elevations and nests, with larger soldiers occurring at localities in intermediate elevations. Heritabilities varied when they were estimated with all data together or separated by locality, showing low-to-intermediate values, while co-heritabilities were intermediate to high. The nonlinear cline found in this study could be a result of the interactions among the factors generating Bergmann’s patterns, such as temperature, the ecology of leaf-cutting ants (management of temperature inside nests) and resource availability. The heritability results imply a genotype-environment interaction, with an overall greater effect of the environment on body size variation in A. cephalotes soldiers.

Beauveria bassiana for the control of leafcutter ants: strain and host differences

ABSTRACT Leafcutter ants are a serious pest for forestry plantations and crops in Latin America. They have been traditionally controlled using chemical synthetic pesticides, which are known to have many negative effects to non-target organisms and the environment. Therefore, there is an urgent need for the development of alternative strategies of control, among which the biological control using fungal pathogens is a promising one. We evaluated in laboratory 3 strains of Beauveria bassiana (B5, B6, B7) against workers from 4 to 7 field colonies from 5 species of Acromyrmex leafcutter ant species which are considered pests in the region. Our results showed that all strains were pathogenic, although there are some ant species that turned out to be more susceptible either due to their intrinsic immunity or the natural load of pathogens they carried. The three strains were similarly effective for 3 of the 5 species, A. ambiguus, A. crassispinus, and A. lundii, being responsible for more than 80% of their mortality overriding the effect of their natural pathogens. Only strain B6 was able to kill a similar percentage of ants of A. heyeri, and strain B7 half of them. B5 in A. heyeri, as well as all three strains in A. lobicornis, were responsible for up to 30% of the mortality, but with the additive effect of the pathogens naturally brought by these ants accounted for a 70% of their mortality. We recommend using B6 to test the control of Acromyrmex leaf-cutting ants in the field.

Toxicity and behavioral alterations caused by essential oils of Croton tetradenius and their major compounds on Acromyrmex balzani

Leafcutter ant Acromyrmex balzani is a species responsible for causing important losses in agricultural crops, pastures and forest plantations. Croton tetradenius, an aromatic plant of wide occurrence in northeastern Brazil, is a plant that has great potential as a botanical insecticide for control of leafcutter ants. The present study evaluates the toxicity and sublethal effects of essential oils of C. tetradenius plants from natural populations in the state of Sergipe, Brazil, and their major compounds, applied by fumigation, on A. balzani workers. The essential oils used in the study were obtained from five plants of C. tetradenius and their major compounds - 1,8-cineole, α-pinene, camphor, (E)-pinocarveol and p-cymene-, acquired commercially. All treatments exhibited formicidal activity, with LC50 values ranging from 1.47 to 2.40 μL.L−1 for the essential oils and 0.45–11.20 μL.L−1 for the major compounds. Camphor was the most toxic tested compound. After exposure, there was a reduction in the survival of A. balzani. The highest observed LT50 was 42.91 h for essential oils of plant CRT042. The essential oils and their major compounds repelled and affected the walking behavior of A. balzani workers. The formicidal activity of C. tetradenius essential oil and its major compounds was verified, and we demonstrated that it has potential as a natural insecticide to control A. balzani.

Survey of leaf-cutting ant species in native vegetation and monocultures in the State of Goiás, Brazil

Leaf-cutting ants are distributed exclusively in the Americas. For this study, we sampled different areas of native vegetation and monocultures to survey the leaf-cutting ants that occur in the State of Goiás, and to what environments they are associated. We recorded six species of leaf-cutting ants: Atta sexdens, Atta laevigata, Acromyrmex subterraneus, Acromyrmex disciger, Acromyrmex ambiguus, and Acromyrmex hispidus. The last four were registered for the first time for the State of Goiás.

Description using ultramorphological techniques of the infection of Beauveria bassiana (Bals.-Criv.) Vuill. in larvae and adults of Atta sexdens (Linnaeus, 1758) (Hymenoptera: Formicidae)

Leaf-cutting ants, whose name comes from the habit of cutting leaves and other parts of plants, are dominant herbivores in the Americas, attacking different crops to keep symbiotic fungi (their main food source) in the colony. These ants are soil inhabitants, an environment rich in microorganisms, many of which are considered entomopathogenic. In order to describe a kind of microbial biological control of these ants through histological techniques, we used the fungus Beauveria bassiana (Bals.- Criv.) Vuill. Larvae and adult workers of Atta sexdens (Linnaeus, 1758) were exposed to a fungal suspension with the concentration of 106/conidia/mL. The specimens were adequately prepared to describe the behavior of the fungus on the integument at 24, 48 and 72 hours after initial exposure. Some specimens were used to represent these periods, being properly processed for scanning electron microscopy, which was applied to document the fungus development on the surface of the insect integument. To better understand the dynamics of the fungal infection, from the conidial adhesion to the potential colonization of the insides of the insect, the histological technique with HE staining was applied. The results showed that, in immature individuals, the hyphal penetration of B. bassiana fungi into the insect integument occurred in 48 h.

Longitudinal Study of Foraging Networks in the Grass-Cutting Ant Atta capiguara Gonçalves, 1944.

Colonies of leaf-cutting ants of the genus Atta need to collect large quantities of vegetal substrate in their environment to ensure their growth. They do so by building and extending over time a foraging network that consists of several underground tunnels extending above ground by physical trails. This paper presents a longitudinal study of the foraging network of two mature colonies of the grass-cutting ant Atta capiguara (Gonçalves) located in a pasture in central Brazil. Specifically, we investigated whether the extension of the foraging area of the colonies required to reach new resources occurs by building new and longer underground tunnels or by building new and longer physical trails. Each nest was surveyed at intervals of approximately 15days during 1year. At each survey we mapped the position of the tunnel entrances and foraging trails at which activity was observed. In addition, we assessed the excavation effort of the colonies since the last survey by the number and distance to the nest of new tunnel entrances, and the physical trail construction effort by the number and length of newly built physical trails. Our study reveals that in A. capiguara the collection of new resources around the nest required to ensure the continuous growth of the colonies is achieved mainly through the excavation of new underground tunnels, opening at greater distance from the nest, not through the building of longer aboveground physical trails.

Laboratory acute contact toxicity test with the leafcutter bee Megachile rotundata

So far little is known about the toxicity of Plant Protection Products (PPPs) to solitary bees other than Osmia spp. as well as the inter- and intra-species sensitivity differences of honey bees and solitary bees. Megachile rotundata is a commercially bred solitary bee which is used worldwide mainly for the pollination of alfalfa. In general, bees can be exposed to PPPs directly by contact spray application (overspray) or indirectly via nectar and pollen. The leafcutter bees additionally can be exposed to (possibly) contaminated leaf pieces which are used for the building of brood cells. Therefore, contact toxicity might be of major importance within leafcutter bee species. Acute contact toxicity tests with M. rotundata based on the existing honey bee testing guideline OECD No. 214 were carried out, to make a first step in the direction of the development of a standard test method and collect data for the comparison of inter- and intra-species contact toxicity sensitivity. The toxic reference substance dimethoate was used as test substance. LD50/24h values of M. rotundata were compared to values of A.mellifera generated in a similar period of time. The low mortality observed in the control also after 96 hours, confirms the feasibility and reliability of the test method. The LD50/24h values of M. rotundata in all four tests were higher compared to those of A. mellifera. Accordingly, M. rotundata appeared to be slightly less sensitive to formulated dimethoate than A. mellifera.

How Do Leaf-Cutting Ants Recognize Antagonistic Microbes in Their Fungal Crops?

Leaf-cutting ants employ diverse behavioral strategies for promoting the growth of fungal cultivars in a structure known as fungus-garden. As a nutritionally-rich resource for the ants, the fungal crop is threatened by microbial antagonists and pathogens. Strategies for protecting the garden against harmful microbes have been described in detail, though the process of microbial threat recognition is not fully understood. Here, we review the literature on leaf-cutting ants’ social immunity traits, in search of possibilities by which workers recognize harmful microbes in their system. Based on current data, we suggest mechanisms regarding (1) chemical recognition, where discrimination could be related to chemical cues from the antagonistic microbe or semiochemicals released by the fungus-garden during harmful interactions, or (2) through associative learning when workers would connect the microbe cues with a damage in the fungus-garden, developing a “colony-level memory” towards this threat. We also discuss evidence supporting ant-fungus communication as key for maintaining the health of the fungus-garden, as well as experimental setups for future evaluation of threat detection and recognition by leaf-cutter ants.

A Volatile Semiochemical Released by the Fungus Garden of Leaf-Cutting Ants

The symbiosis between fungi and leaf-cutting ants (Hymenoptera: Formicidae) has aroused the interest of researchers about the mechanism used by ants to select plants. The nutritional needs of the fungus garden, and the absence of potentially deleterious substances from plants, are criteria for selection by foraging workers. This is supported by behavioral experiments using fungicide with baits (citrus pulp) or forage plants highly accepted by leaf-cutting ants. The fungus garden is hypothesized to emit a volatile semiochemical in response to a fungicide, which informs ants that a plant is unsuitable for its growth. The objectives of our study were to identify the volatile compounds released by the fungus garden of leaf-cutting ants in response to a fungicide, as well as to determine the behavioral response of workers to healthy and unhealthy fungus gardens. The results showed no difference in the proportion of volatile compounds released by either healthy or unhealthy fungus gardens. Analysis of the responses of ants to healthy or unhealthy fungus gardens in a dual-choice experiment revealed a strong attraction to the fungus garden, regardless of its health status. We therefore conclude that no volatile semiochemicals are emitted by the fungus garden due to the action of deleterious substances.

Seasonal Parasitism of the Leaf-Cutting Ant Atta sexdens Linnaeus (Hymenoptera: Formicidae) by Phorid Flies (Diptera: Phoridae) in a Brazilian Cerrado-Atlantic Forest Ecotone

Phorid flies (Diptera: Phoridae) parasitize insects of many orders including leaf-cutting ants, which are pests of several crops. These parasitoids may have a significant impact on ant behavior by altering their foraging rhythm. Seasonal variations in climatic variables, such as temperature and humidity, influence the abundance, activity period, distribution, and reproduction of insects. Therefore, knowledge of parasitoid seasonal patterns is important for biological control success. In this study we evaluate the parasitism of the leaf-cutting ant Atta sexdens L. (Hymenoptera: Formicidae) by Apocephalus attophilus Borgmeier and Eibesfeldtphora tonhascai Brown (both Diptera: Phoridae) across seasons throughout a yr in a Brazilian Cerrado-Atlantic Forest ecotone, and compare their parasitism in a semi-deciduous seasonal forest fragment and urban area. The number of ants parasitized by A. attophilus and E. tonhascai was higher in the winter and spring, respectively, but similar in summer and fall. Apocephalus attophilus parasitism was negatively correlated with temperature but not with relative humidity, whereas ant parasitism by E. tonhascai presented no correlation with either parameter. The number of ants parasitized by A. attophilus and E. tonhascai in the semi-deciduous seasonal forest fragment was higher than in urban areas. Knowledge of biotic and abiotic factors influencing the population dynamics of phorid flies is important for rearing and releasing protocols for these parasitoids.

Leaf‐cutting ants negatively impact the regeneration of the Caatinga dry forest across abandoned pastures

AbstractThe mechanisms affecting forest regeneration in human‐modified landscapes are attracting increasing attention as tropical forests have been recognized as key habitats for biodiversity conservation, provision of ecosystem services, and human well‐being. Here we investigate the effect of the leaf‐cutting ants (LCA) Atta opaciceps on regenerating plant assemblages in Caatinga dry forest. Our study encompassed 15 Atta opaciceps colonies located in landscape patches with a gradient of forest cover from 8.7% to 87.8%, where we monitored regenerating individuals (seedlings and saplings of woody and herbaceous plants) in different habitats (nests, foraging areas, and control areas) over one year. We recorded 2,977 regenerating plant individuals, distributed among 55 species from 23 families. Herbaceous plants represented 82.1% and 58.2% of the total number of individuals and species, respectively. Species richness of both the whole and herbaceous plant assemblages increased along the forest cover gradient, but without difference between the habitats. Total plant abundance was highest in control areas followed by foraging areas and nests and this pattern held for both woody and herbaceous plants. Although forest cover did not influence the abundance of herbaceous plants and the whole plant assemblage, it positively affects woody plant abundance across control areas. Forest cover and habitat changed species composition of both the entire regenerating and the herbaceous assemblages. These results together indicate that LCA negatively impact regenerating plant assemblages, particularly in those sites with increased forest cover. As LCA proliferate in human‐modified landscapes, they may prevent plant regeneration of disturbed areas.

Phytochemical characteristics of leaves determine foraging rate of the leaf-cutting ant Atta mexicana (Smith) (Hymenoptera: Formicidae)

Atta mexicana is a polyphagous insect that can exploit a wide range of plant species to cultivate its main food source, the symbiotic fungus Leucoagaricus gongylophorus. In the present study, we evaluated the foraging rate of A. mexicana workers among leaves of three favored and three rejected plant species under laboratory conditions. In addition, we conducted a phytochemical characterization of leaves of these six plant species. Ants preferred leaf discs of Rosa × alba, Trema micrantha and Styrax glabrescens, but rejected those of Coffea arabica, Citrus reticulata and Psidium guajava. In a second behavioral experiment using plant extracts, the results suggest that in the case of C. reticulata, rejection was not due chemical composition, but may have been due to different foliar attributes that could modulate the ant’s foraging preferences in this species. Alkaloids, phenols, flavonoids, and tannins were present at different concentrations in all six plant species. Furthermore, C. arabica leaves presented significantly higher concentrations of alkaloids and this species, together with P. guajava, exhibited the highest concentration of phenols. Rejected plant species showed high concentrations of chlorogenic acid, (−)-epicatechin, quercetin-3, 4-di-O-glucoside (in C. arabica); shikimic acid, ellagic acid and (−)-epicatechin (in P. guajava), and scopoletin (in C. reticulata). Some of the identified compounds have been shown to possess antifungal effects and/or to dissuade leaf-cutter ants from defoliation. We discuss the likely implications on foraging on such plant species by A. mexicana, and on the growth of its symbiotic fungus.