Interference of beta-eudesmol in nestmate recognition in Atta sexdens rubropilosa (Hymenoptera: Formicidae)

Leaf-cutter ant species (Atta spp.) are key pests of cultivated crops in the Neotropics, and recent studies have demonstrated that workers of Atta spp., particularly of Atta sexdens rubropilosa, exhibit aggressive behavior among nestmates when in contact with the sesquiterpene beta-eudesmol, found in leaves of Eucalyptus maculata. However, the underlying mechanism sparking this behavior pattern has yet to be investigated. This work aimed to elucidate the mechanism by which this substance elicits aggression in workers of A. sexdens rubropilosa. The results, thus obtained, showed that beta-eudesmol is able to modify the chemical composition of the workers cuticle, impairing nestmate recognition, triggering alarm behavior and leading to nestmate aggression.     

The influence of the scout upon the decision-making process of recruited workers in three Acromyrmex species (Formicidae: Attini)

We examined how the information communicated by a scout worker influences the plant species transported by recruited workers in Acromyrmex balzani, Acromyrmex rugosus, and Acromyrmex crassispinus, three species of leaf-cutting ant that have different substrate and habitat preferences. We verified that certain plant species were more likely to be transported than others and that recruitment occurs. We found that recruited workers were more likely to transport non-preferred plant species when they were recruited to these by scout workers. The results suggest that the scout worker can communicate information about plant identity to recruited workers, but that recruited workers integrate the information communicated with their own experience during the decision-making process.     

Electrophysiological responses of Atta sexdens rubropilosa workers to essential oils of eucalyptus and its chemical composition

The leaf-cutting ant Atta sexdens rubropilosa Forel, 1908 is the most harmful of the Eucalyptus pests, causing severe losses in wood production through defoliation. Various strategies have been tried and effort spent on the development of methods to control this pest, however no practical and environmentally acceptable one currently exists. In this work the chemical composition of the essential oil of seven Eucalyptus species was identified and the selectivity and sensitivity of antennal receptors of A. sexdens rubropilosa workers to the volatile compounds were determined using the electroantennographic technique (EAG and GC-EAD). Analysis by GC-EAD showed in E. cloesiana and E. maculata, respectively, seventeen and sixteen terpenes that elicited responses in ant workers' antennae, indicating the potential role of the essential oils as allelochemicals that determine the choice of the foraging material.     

Forager size of the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae) in a mature eucalyptus forest in Brazil

We determined the size characteristics of foragers of the leaf-cutting ant Atta sexdens in a mature eucalyptus forest in Campos dos Goytacazes, Rio de Janeiro State, Brazil, at daytime (7:30 to 10:00 hr) and nighttime (19:00 to 23:00 hr). There were no significant differences between daytime and nighttime ant mass (Ma), but leaf fragment mass (Ml) and burden (B = [Ma + Ml]/Ma), which indicates relative load capacity, were significantly greater at daytime. There was a positive linear relationship between Ma and Ml for the combined daytime and nighttime data, and increases in Ma resulted in lower B. We compared A. sexdens characteristics with published results for Atta cephalotes, a closely related species. A. sexdens is larger and therefore able to carry heavier loads, but its burden is about 72% of the average value for A. cephalotes. We suggest that the lower load capacity of A. sexdens in comparison to A. cephalotes is related to its relatively larger size.     

Occurrence and biological characteristics of parasitoid phorids (Diptera: Phoridae) of the leaf-cutting ant Atta laevigata (Smith) (Hymenoptera: Formicidae) in Porto Nacional, TO, Brazil

The purpose of this study was to verify the occurrence of parasitism in Atta laevigata (Smith) by phorids in Porto Nacional, Tocantins, Brazil and to evaluate some biological characteristics of those flies. From October/2002 to September/2003, at 15-day intervals, 22 samplings were carried out (149.5 +/- 82.9 workers each) comprising 3,704 ants. In the laboratory, the ants were distributed in groups of five individuals per petri dish and maintained at temperature of 25 +/- 1 masculineC and 80 +/- 5% of RH. They were fed daily with a 50% honey solution until death. The total of 106 workers (2.8%), collected with or without load (plant fragment), were parasitized by phorids: 72 workers (68%) were parasitized by Apocephalus vicosae Disney, 28 individuals (26.4%) by Neodohrniphora erthali Brown, and six (5.6%) by Apocephalus attophilus Borgmeier. The higher parasitism rates by A. vicosae (3.9-5.4%) were observed during the dry season (June-August), while the parasitism by N. erthali was lower than 2.3% throughout the year. The bigger workers were parasitized by bigger parasitoid N. erthali or by parasitoid with larger number of larvae A. attophilus. The occurrence of three phorid species in Tocantins broadens the distribution of these flies in Brazil. The development of A. vicosae larva within the thorax of the host as well as the rupture between the ant pronotum and propleuron so that the emergence of the fly can take place are characteristics not yet described on parasitism of leaf-cutting ants by phorids.     

Effect of constituents of the foliar wax of Didymopanax vinosum on the foraging activity of the leaf-cutting ant Atta sexdens rubropilosa

Leaf epicuticular waxes may affect substrate selection by leaf-cutting ants, and host recognition by several phytophagous insects. The influence of the crude epicuticular wax of Didymopanax vinosum E. March. (Araliaceae), and its major constituents lupeol and free primary alcohols, on substrate selection by the leaf-cutting ant Atta sexdens rubropilosa Forel, was investigated. Two ant colonies were used in laboratory bioassays. Corn flakes (zea) were impregnated with chloroform solutions of the substances being tested and fed to the adults. One of the colonies gave results, in most of the tests, not significantly different from the controls. The other colony, however, discriminated against the crude wax, a strong deterrent effect being observed from the first of a series of eight trials. The same colony was able to discriminate against lupeol after the second trial. The fraction of primary n-alcohols (22% C₂₈, 66% C₃₀ and 12% C₃₂) deterred feeding only after the fifth trial. The results demonstrate that some constituents of epicuticular waxes may deter the foraging activity of A. sexdens rubropilosa, depending, however, on the colony under observation. It is suggested that lupeol, of the foliar wax of D. vinosum, is an important deterrent to leaf-cutting ants, although with less pronounced effects than those observed in tests with the crude wax.     

Seasonal Activity and Foraging Preferences of the Leaf-Cutting Ant Atta sexdens piriventris (Santschi) (Hymenoptera: Formicidae)

Leaf-cutting ants are known for their habit of foraging. These habits can be influenced by several factors, including variations in topography, soil, and climate among others. The objective of this research was to study the seasonal activity and foraging preferences of the leaf-cutting ant Atta sexdens piriventris (Santschi). The study was carried out from January to October of 2007 in grasslands of the state of Santa Catarina, Brazil. Nests of A. sexdens piriventris were randomly selected and the forager’s activities were recorded. Damaged plant species, soil fertility, and climatic conditions were recorded. The maximum foraging activity in the summer was recorded during periods of darkness or low light (between 7 p.m. and 5 a.m.). In autumn and spring, foraging was the highest in the morning, but during winter time the foraging activity was high in the afternoon. Fourteen plant species were frequently visited during our study with the lowest foraging activity being recorded at very low (1 to 4°C) or very high temperatures (above 26°C). The number of exploited plant species was higher in winter (13) than in summer (9). Baccharis trimera (Asteraceae) (43%) and Paspalum spp. (Poaceae) (33%) were the most exploited plants among the identified species.     

The role of the symbiotic fungus in the digestive metabolism of two species of fungus-growing ants

Leaf-cutting ants live in an obligatory symbiosis with a fungus which they grow on fresh leaves harvested by workers. This study attempts to clarify the respective role of ants and fungus in the degradation of plant material, in order to highlight the evolutionary basis of this mutualistic association. The symbiotic system of two ant species, Acromyrmex subterraneus subterraneus and Acromyrmex crassispinus, was investigated. To identify the digestive carbohydrases, a total of 19 specific and synthetic plant material substrates were tested on workers from different castes (major and minor), larvae and fungus. Extracts of A. subterraneus and A. crassispinus workers showed high enzymatic activity particularly on starch, maltose, sucrose and alpha-1,4 glucoside. Larvae degraded starch, sucrose, maltose but also laminarin, and all the detected activities were higher than those found for workers. The symbiotic fungus of A. subterraneus was mostly active on laminarin, xylan and cellulose, while the symbiotic fungus of A. crassispinus was mostly active on laminarin, starch, maltose and sucrose. The enzymatic activities of ants and fungus belonging to the same symbiotic system tended not to overlap, suggesting that the association is highly evolved and of an ancient origin.     

Behavioural and olfactory variations in the leek moth, Acrolepiopsis assectella, after several generations of rearing under diverse conditions

Females of the parasitic phorid Neodohrniphora sp. were collected in the field and released singly inside an observation chamber placed between a laboratory colony of Atta sexdens (L.) and its foraging arena. The number and speed of loaded and unloaded ants returning to the nest, the weight of foragers and their loads, the number of leaf fragments abandoned by ants, and the number of small workers 'hitchhiking' on leaf fragments were measured before phorids were released, while they were in the observation chamber, and after they were removed. Relatively few ants were attacked by Neodohrniphora sp., but the presence of flies prompted outbound ants to return to the nest and caused a significant reduction on the number and mass of foragers. Additionally, the weight of leaf fragments transported by ants was reduced and the number of abandoned fragments increased in response to Neodohrniphora sp. Presence of the parasitoid caused no significant changes in the number of hitchhiking ants. The regular ants' traffic was resumed after phorids were removed, but foraging activity remained below normal for up to three hours. In the field A. sexdens forages mostly at night, but colonies undergo periods of diurnal foraging during which ants are subject to parasitism from several species of phorid flies. Considering that daytime foraging may be necessary for nutritional or metabolical needs, phorids may have a significant impact on their hosts by altering their foraging behavior regardless of the numerical values of parasitism.     

Response of workers of Atta sexdens rubropilosa (Hymenoptera: Formicidae) to mandibular gland compounds of virgin males and females

Abstract.  The secretion from the mandibular glands of males of the leaf-cutting ant Atta sexdens rubropilosa is responsible for the reaction of workers outside the nest at the time of sexual swarming. Workers respond with excitability and aggression when presented with the natural mixture of 4-methyl-3-heptanol and 4-methyl-3-heptanone, which is contained in the secretion of the male mandibular glands. Workers respond quickly to fractional amounts of one male equivalent. 4-Methyl-3-heptanone, from the virgin female mandibular glands causes much less response in workers, whereas an equimolar mixture of male and female pheromones gives a still less clear response. The male pheromone plays the most important part in the communication of workers outside the nest at this time.     

Toxic effects of Canavalia ensiformis L. (Leguminosae) on laboratory colonies of Atta sexdens L. (Hym., Formicidae)

Laboratory colonies of the leaf-cutting ants Atta sexdens that were fed daily with leaves of Canavalia ensiformis showed a high ant mortality, and a significant decrease in fungal garden volume, with complete depletion of nests after 11 weeks of treatment.     

Foraging and leaf-cutting of the desert gardening ant Acromyrmex versicolor versicolor (Pergande) (Hymenoptera: Formicidae)

Summary Four colonies of the desert leaf-cutter ant Acromyrmex versicolor versicolor (Pergande) located 30 miles N.E. of Tempe, Arizona were observed over a 7 month period. The ants utilized trails in foraging, a characteristic of higher attines, as well as foraging singly, a typical pattern among the more primitive gardeners. The ants cut and collected both dry and green vegetation with dry grasses comprising the bulk of the forage. The ants increased their cutting of green vegetation after significant rainfall but collected dry grasses almost exclusively during dry periods. Detailed macro-motion picture analysis of leaf-cutting revealed that the desert gardener utilized a unique technique for cutting compound desert leaves.     

Chemical and behavioural studies of the trail-following pheromone in the leaf-cutting ant Atta opaciceps,Borgmeier (Hymenoptera: Formicidae)

To understand the significance of the trail pheromone used in chemical communication of the leaf-cutting ants Atta opaciceps we investigated, under laboratory conditions, the trail-following behaviour of different castes. We observed a clear behavioural discrimination of conspecific venom gland extract of foraging ants from those of other species. Additionally, we determined the pheromone composition of A. opaciceps venom gland secretion using a two-dimensional gas chromatography coupled with mass spectrometry. Chemical analyses revealed the presence of three nitrogen-containing compounds, identified as 2,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine and methyl 4-methylpyrrole-2-carboxylate (M4MPC). Four different bioassays performed with workers from different castes of A. opaciceps suggested that the trail pheromone elicits the trail-following behaviour in conspecifics of all castes, but the foragers respond more strongly to their own pheromone than to that of other castes (gardeners, generalists and soldiers). In addition, A. opaciceps foragers follow the trails made with the venom gland extracts of the unrelated Acromyrmex subterraneus subterraneus foragers as well as they follow the trails made with their own venom gland extract. M4MPC was identified to be the most abundant and the most behaviourally active component of the venom gland extract of A. opaciceps foragers.     

Plants use macronutrients accumulated in leaf-cutting ant nests

Leaf-cutting ants (Atta spp.) are known for their extensive defoliation in neo-tropical forests and savannahs. Debate about the costs and benefits of their activities has been largely dominated by their detrimental effects on agriculture and agroforestry. However, the large accumulation of nutrients and changes in soil properties near their nests might benefit plants growing near them. Here, we test whether trees use nutrients that accumulate in debris piles near, or refuse chambers within, leaf-cutting ant nests. At two tropical sites (a moist tropical forest site in Panama and a savannah site in Brazil), we fed leaves labelled with the stable isotope 15N to two species of leaf-cutting ants (Atta colombica and Atta laevigata) and traced the stable isotope label in plants surrounding the two nests. Thus, we show that plants in both sites access resources associated with Atta nests. In addition, leaf tissue of trees near the nests labelled with 15N had significantly higher calcium concentrations than those of distal, unlabelled conspecifics. It has been documented that calcium is a limiting macronutrient in tropical forests and savannahs. Atta may thus play an important ecological role through their long-distance transport, redistribution and concentration of critical macronutrients.     

The epizootiology of a Metarhizium infection in mini-nests of the leaf-cutting ant Atta sexdens rubropilosa

There is growing interest in the use of entomopathogenic organisms to control leaf-cutting ants (Hymenoptera: Formicidae: Attini). However, the way leaf-cutting ants react as a colony to biohazards is poorly understood. We investigated the effects of Metarhizium anisopliae (Metschnikoff) (Deuteromycotina: Hyphomycetes) applied to the foraging arenas of mini-nests (queenless sub-colonies) of the leaf-cutting ant Atta sexdens rubropilosa (Forel). Dry spores were applied either alone or mixed with citrus powder, at 0.5 g or 0.05 g per mini-nest. The spores were removed four days after application, and all dead ants removed every three days. Ant numbers near the Metarhizium increased as the ants attempted to clean up the biohazard. The ants attempted to place the spores in piles, which they then covered over with other material. They were able to deal with the low doses in this way, but the high doses overwhelmed them. All treated mini-nests suffered increased ant mortality during the first ten days after application. This mortality was particularly high in the media worker caste which had played the major role in attempting to clean up the spores. Foraging activity decreased, as did the health of the fungus gardens. The mini-nests exposed to the low dose of spores mixed with citrus powder then recovered fully. The health of the other treated mini-nests declined gradually until around 26 days after application, when they began deteriorating sharply. However, the decline of these mini-nests after day 26 was not due directly to the pathogenic action of the Metarhizium, nor to the initial ant mortality it had caused. The results suggest that the social stress caused by even such a short-lived Metarhizium epizootic was sufficient to cause the decline and ultimate death of the mini-nests. This has important implications for the control of leaf-cutting ants. It also demonstrates how important the social homeostasis of the colony is to leaf-cutting ants.     

Colony behavior of Atta sexdens rubropilosa (Hymenoptera: Formicidae) in the absence of the queen under laboratory conditions

A colony of Atta sexdens rubropilosa was studied in the presence and absence of the queen. The frequency of 23 previously defined behaviors was quantified in terms of average frequencies of act occurrence. Colony behavioral activities such as foraging, fungal care, and refuse manipulation were not directly influenced by the queen's presence up to 30 days after the queen's death. The queen, which also seems to maintain colony cohesion aside from reproduction, indirectly affected brood care.     

Spatial and Temporal Variation of Plant Fragment Removal by Two Species of <Emphasis Type="Italic">Atta</Emphasis> Leaf-Cutting Ants

Leaf-cutting ants are responsible for much of living plant fragment removal in Neotropical regions, causing major damage in both in natural and agricultural systems. To understand the variation in plant fragment removal by leaf-cutting ants and the influence that temporal and spatial factors have on such variation, we evaluated plant fragments collected by two ant species, Atta laevigata and A. sexdens rubropilosa in different seasons (rainy and dry) and in different forest systems (natural area of cerrado sensu stricto and monoculture of Eucalyptus sp.) in 2014 in Goianésia, Goiás, Brazil. Heavier plant fragments were removed during the dry season and in monoculture areas; A. laevigata removed heavier fragments than A. sexdens rubropilosa. Furthermore, we observed a positive association between the weight of collected fragments and the weight of worker ants and higher weights in A. laevigata. The study shows that the weight of plant fragments removed by leaf-cutting ants is conditioned temporally and spatially, and by the ant species involved. More detailed studies of each of these factors are need to better understand the dynamics of these foraging ants and how abiotic and biotic factors affect this process.     

Life-history traits and parasitism rates of four phorid species (Diptera: Phoridae), parasitoids of Atta vollenweideri (Hymenoptera: Formicidae) in Argentina

Leaf-cutting ants in the genus Atta F. (Formicidae, Attini) are among the most important pest arthropods in Central and South America, consuming more vegetation than any other animal group. Among the organisms attacking ants in nature, flies of the family Phoridae have been proposed as the most promising biocontrol agents for pest ants. Four phorid species, Apocephalus setitarsus Brown, Myrmosicarius brandaoi Disney, Myrmosicarius gonzalezae Disney, and Eibesfeldtphora trilobata Disney, were reared from ants collected at Atta vollenweideri Forel nests and off foraging trails in Santa Fe province in Argentina. E. trilobata attacked larger ants and had bigger adults than the other species, also exhibiting the longest developmental time. Correlations between size of hosts and size of adults, as well as between size of adults and developmental times, could be established only in some cases. No differences were found between the sizes of the hosts from which males and females emerged. The natural percentage of parasitism varied throughout the seasons and seemed to be influenced by the extreme drought affecting the study site. We discuss why all four species would be suitable candidates for integrating an assemblage of biocontrol agents against A. vollenweideri.     

The Behavior of <Emphasis Type="Italic">Acromyrmex crassispinus</Emphasis> (Hymenoptera: Formicidae) on Trail Bifurcations and the Influence of Ant Flow on Error Rates of Nestbound Laden Workers

Ants are ordinarily faced with a succession of bifurcations along their foraging networks. Given that there is no directionality in pheromone trails, each bifurcation is potentially an opportunity for error in the trajectory of laden workers to the nest, which could entail considerable inefficiencies in the transportation of food to the colony. Leaf-cutting ants (Atta and Acromyrmex) commonly show intense traffic and complex foraging trail systems, which make them ideal organisms to study worker behavior in trail bifurcations. The behavior of leaf-cutting ants of the genus Acromyrmex in trail bifurcations is still largely unexplored. Thus, this study aimed to assess the behavior of Acromyrmex crassispinus workers on trail bifurcations and to investigate whether differences in ant flow on foraging trails influence the error rate of nestbound laden workers at trail bifurcation. There was a negative relationship between ant flow and error rate of nestbound laden workers. Most workers walked in the central part of the foraging trails but occupied a broader area of the foraging trail when the ant flow was high. The results of this study provide valuable insight into the organization of traffic flow in A. crassispinus and its impacts on the foraging strategy of the species.