Leaf-cutting Ant Acromyrmex Octospinosus Research Articles

Sustainable Management of Acromyrmex octospinosus (Reich): How Botanical Insecticides and Fungicides Should Promote an Ecofriendly Control Strategy.

The leaf-cutting ant Acromyrmex octospinosus (Reich) causes serious damage to crops and protected areas due to its foraging activity. The main method of control of this species consists of the use of synthetic insecticides that can lead to environmental damage and negative side effects on human health. Consequently, alternative strategies, such as biopesticides, are needed. Insecticide evaluation by ingestion assays was performed using A. octospinosus in vitro bioassay and laboratory nests. Chemical analyses were also performed to know the contents of plant extracts. This study showed that Mammea americana L. is the most promising insecticidal plant extract in the control of A. octospinosus. Indeed, the lethal concentrations (LC50 and LC99) an the lethal dose (LD99) of the M. americana extract (51.31 mg.mL-1, 131.92 mg.mL-1, and 17.36 mg/g of ant respectively) were the closest to those of Fipronil, 0.03 g/kg, the commercial insecticide used as positive control.

Dynamic Wolbachia prevalence in Acromyrmex leaf‐cutting ants: potential for a nutritional symbiosis

Wolbachia are renowned as reproductive parasites, but their phenotypic effects in eusocial insects are not well understood. We used a combination of qrt-PCR, fluorescence in situ hybridization and laser scanning confocal microscopy to evaluate the dynamics of Wolbachia infections in the leaf-cutting ant Acromyrmex octospinosus across developmental stages of sterile workers. We confirm that workers are infected with one or two widespread wsp genotypes of Wolbachia, show that colony prevalence is always 100% and characterize two rare recombinant genotypes. One dominant genotype is always present and most abundant, whereas another only proliferates in adult workers of some colonies and is barely detectable in larvae and pupae. An explanation may be that Wolbachia genotypes compete for host resources in immature stages while adult tissues provide substantially more niche space. Tissue-specific prevalence of the two genotypes differs, with the rarer genotype being over-represented in the adult foregut and thorax muscles. Both genotypes occur extracellularly in the foregut, suggesting an unknown mutualistic function in worker ant nutrition. Both genotypes are also abundant in the faecal fluid of the ants, suggesting that they may have extended functional phenotypes in the fungus garden that the ants manure with their own faeces.

Polymorphism and Division of Labor During Foraging Cycles in the Leaf-cutting Ant Acromyrmex octospinosus (Formicidae; Attini)

While division of labor within leaf-cutting ant nests has been well-characterized in the context of the collection and processing of leaf material, environmental factors such as day-night cycles and heavy rainfall limit the time during which leaf-cutting ant workers leave the nest to gather forage. Using a novel “flat panel” nest design, we studied how patterns of within-nest task performance changed when a colony of the leaf-cutting ant Acromyrmex octospinosus was and was not provided access to forage. We conducted scan samples of individuals working within the nest under both conditions and compared task allocation patterns across provisioning regimes and between workers of different sizes. When labor was compared between worker size groups, “minor” workers (head width ≤2.0 mm) and “major” workers (head width >2.0 mm) showed significantly different task performance patterns when forage was available: minors performed mostly brood-care and garden maintenance, while majors were mostly involved in the handling of freshly-cut leaf fragments. In contrast, when the colony was deprived of forage, the task performance patterns of minor and major workers converged and did not significantly differ. Marked major workers known to be foragers tended to remain idle within the nest when the colony was deprived of forage, while non-foragers of similar head width engaged in a variety of within-nest tasks, suggesting polyethism in majors may be based on factors other than size.

The effects of age and social interactions on innate immunity in a leaf-cutting ant

Both developmental and environmental factors shape investment in costly immune defences. Social insect workers have different selection pressures on their innate immune system compared to non-social insects because workers do not reproduce and their longevity affects the fitness of relatives. Furthermore, hygienic behavioural defences found in social insects can result in increased survival after fungal infection, although it is not known if there is modulation in physiological immune defence associated with group living vs. solitary living. Here we investigated whether physiological immune defence is affected by both age and the short-term presence or absence of nestmates in the leaf-cutting ant Acromyrmex octospinosus. We predicted that older ants would show immune senescence and that group living may result in prophylactic differences in immune defence compared to solitarily kept ants. We kept old and young workers alone or in nestmate groups for 48 h and assayed a key innate immune system enzyme, expressing phenoloxidase (PO) and its stored precursor (proPO), a defence that acts immediately, i.e. it is constitutive. Short-term solitary living did not affect PO or proPO levels relative to group living controls and we found no evidence for immunosenescence in proPO. However, we found a significant increase in active PO in older workers, which is consistent with two non-mutually exclusive explanations: it could be an adaptive response or indicative of immunosenescence. Our results suggest that future studies of immunosenescence should consider both active immune effectors in the body, such as PO, and the stored potential to express immune defences, such as proPO.

Nest-founding in Acromyrmex octospinosus (Hymenoptera, Formicidae, Attini): demography and putative prophylactic behaviors

Foundresses of the leaf-cutting ant Acromyrmex octospinosus in central Panama forage for leaves as garden substrate (semi-claustral foundation). The fungal pellet and substrate usually are attached to rootlets, which are used as a platform for the garden. This arrangement keeps the garden suspended away from the earthen chamber of the underground nest during early colony growth, and we hypothesize that it serves to minimize contact between the garden and contaminants. A. octospinosus foundresses produce from 3 to 7 workers in 2.7 months after founding the nest, but workers do not forage for substrate at this time. Incipient nests died or were abandoned at a monthly rate of ca. 50%. We show that ants routinely clean their legs before manipulating the garden substrate. We also describe how foundresses use their fore-legs to rub the surface of the metapleural gland (MPG), and they then use typical grooming behaviors to pass the forelegs through the mouthparts, after which the ant then licks the garden substrate. Similarly, ants apparently use their mouths to transfer fecal droplets to their legs. We briefly discuss the functional significance of these grooming behaviors, and hypothesize that they are prophylactic behaviors that may help the foundress maintain a hygienic garden.

Lack of patriline-specific differences in chemical composition of the metapleural gland secretion in Acromyrmex octospinosus

Multiple queen-mating (polyandry) in social insects increases the genetic variability among worker offspring, which may enhance colony survival, social productivity and defence against parasites. The unique and complex symbiosis of leaf-cutting ants with a clonal mutualistic fungus makes this social system particularly vulnerable to contamination by pathogenic and unwanted saprophytic fungi and bacteria. Proper defence against such threats requires effective and flexible chemical defence mechanisms. A prime candidate for providing such defences is the metapleural gland secretion, which is known to have broad antibiotic properties. Here we use the leaf-cutting ant Acromyrmex octospinosus to specifically test the hypothesis that genetically more diverse worker-offspring produce a more variable spectrum of metapleural gland compounds. We used DNA microsatellite markers to assign workers from two colonies to the six most common patrilines in each colony, and have analysed the degree to which the observed variance in the quantitative chemical composition of the metapleural gland secretion can be explained by genetic differences among patrilines. We found a marginally significant patriline-effect on the overall variability of metapleural gland compounds in one colony, but could not detect such effect in the other colony. We discuss a number of possible reasons why the genetic variance component for quantitative variation in metapleural gland secretion may be low.

Variable sensitivity of fungi and bacteria to compounds produced by the metapleural glands of leaf-cutting ants

Ants are the only group of insects that have metapleural glands. Secretions of these exocrine glands are known to have antibiotic properties and have been hypothesised to function as a general defence against microbial and fungal infections. Such defences are likely to be particularly important in leaf-cutting ants that need to protect both themselves and their clonal mutualistic fungus against pathogens. The metapleural gland of the leaf-cutting ant Acromyrmex octospinosus produces an array of organic compounds (Ortius-Lechner et al., 2000), suggesting that different compounds may be effective against different kinds of infections. Here we provide a detailed analysis of the sensitivity of two species of bacteria and seven species of fungi (including the mutualistic fungus) to these metapleural gland compounds, grouped in seven classes: acetic acid, short chain acids, medium chain acids, long chain acids, indoleacetic acid, γ-lactones and γ-ketoacids. All classes of compounds inhibited the growth of at least some of the tested micro-organisms. Cluster analysis produced four groups of micro-organisms differing in their overall sensitivity. Among-cluster differences explained a major part of the total variation in sensitivity (MANOVA), although differences between micro-organisms within clusters were also significant. Fungal hyphae and fungal spores never clustered together, indicating that defence mechanisms against these fungal life stages are fundamentally different. The mutualistic fungus was sensitive to all classes of compounds, which suggests that defence via metapleural gland secretion is under constraint when the protection of the fungus garden is concerned.

Functional morphology of the metapleural gland in the leaf-cutting ant Acromyrmex octospinosus

The metapleural gland is unique for ants and its main function is the production of antibiotics. The gland is considered to be of particular significance in leaf-cutting ants, which need to protect both themselves and their clonally reproducing fungal symbiont from pathogens and microbial competitors. In a detailed study of the histology of the metapleural gland of the leaf-cutting ant Acromyrmex octospinosus the diameter of the storage room (bulla) is shown to be highly positively correlated (r = 0.84) with the number of secretory cells inside the gland. This justifies the use of the easily obtainable bulla diameter as an approximation of the size of the actual metapleural gland in e.g. studies of gland allometry. Histological cross sections also show that contraction of the rather massive thoracic muscles may lead to compression of the collection chamber of the metapleural gland and may thus allow active enhancement of the flow of gland secretion to the reservoir behind the bulla.

Foraging Ecology of the Leaf-Cutting Ant Acromyrmex Octospinosus in a Costa Rican Rain Forest

Foraging Ecology of the Leaf-Cutting Ant Acromyrmex Octospinosus in a Costa Rican Rain Forest

A new matrix for toxic baits for control of the leaf-cutting ant Acromyrmex octospinosus (Reich) (Hymenoptera: Formicidae)

AbstractA new easily-produced cheap compound for use as a bait matrix is described. The light-weight matrix of polyurethane is prepared from dense precursors into which suitable attractants and toxicants can be incorporated for the pest species in question. It has a high bait effectiveness/weight ratio, and so is very suitable for aerial application as large economically viable payloads can be achieved. When tested both in the laboratory and in the field on a small scale against the leaf-cutting ant Acromyrmex octospinosus (Reich), the bait was highly acceptable to the ants. Some formulations, especially those coated with mirex gave excellent control of ants in the field in Trinidad, killing all occupants of nests within four days of baiting. The bait exhibited good weathering properties, was resistant to fungus attack, and allowed the slow release of pheromones. It was much cheaper than the citrus pulp baits normally used in Trinidad.

Intraspecific aggression is the leaf-cutting ant Acromyrmex octospinosus

In the field, individuals of Acromyrmex octospinosus taken from widely separated nests are much more hostile towards one another than ants taken from local ones. Individuals taken from different laboratory colonies which have been foraging similar plant material do not fight, but if the colonies are supplied with different forage materials mutual investigation by workers increases with time until aggression is exhibited. However, if colonies are split into two and maintained on different forage, non-injurious aggression occurs when they are recombined. It is suggested that in this ant species both endogenous (genetic) and exogenous (environmental) factors contribute to colony odour, the latter being the more important. In the recognition of strange workers, the two factors appear to synergize each other.

Studies on the role of the infrabuccal pocket of the leaf-cutting antAcromyrmex octospinosus (Reich) (Hym., Formicidae)

The leaf-cutting antAcromyrmex octospinosus was shown to filter out into its infrabuccal pocket from liquid food, particles down to ten μ in diameter. The pocket acted as a receptacle for material licked from the ants' fungus garden and from their own bodies, and for leaf wax licked from leaves used for fungus culture. The infrabuccal pellets of worker ants, which might contain contaminating fungal spores, were always found away from the fungus garden and mostly on the refuse dump. Virgin queens however, regurgitated their pellets onto the fungus garden. Pellets regurgitated by worker ants were streaked onto agar plates, and from these the ant fungus was cultured. Worker ants were not able to start a new fungus garden, but the use of the infrabuccal pocket by queens to transmit the ant fungus to newly founded colonies can be seen as part of a general behaviour pattern.

The effects of diet on the composition of the post-pharyngeal glands ofAcromyrmex octospinosus (Reich)

In the leaf-cutting antAcromyrmex octospinosus, the post-pharyngeal glands of workers are filled with a yellow oil, whereas the same gland in alate ants contains a colourless oil. This difference between castes is due to different diets. The colouration in worker glands disappears when a colony is fed on unpigmented substrate. Radioactive tracer studies showed that certain plant materials, probably lipids, enter the post-pharyngeal glands during leaf-chewing. The rapidity with which the gland become radiolabelled indicates that these materials enter the gland directly. Experiments with vitally coloured food show that only the liposoluble fraction of the diet enters the gland.