Ventilation of the giant nests of Atta leaf-cutting ants: does underground circulating air enter the fungus chambers?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Temporal patterns of nutrient availability around nests of leaf-cutting ants (Atta colombica) in secondary moist tropical forest

Leaf-cutting ants consume up to 10% of canopy leaves in the foraging area of their colony and therefore represent a key perturbation in the nutrient cycle of tropical forests. We used a chronosequence of nest sites on Barro, Colorado Island, Panama, to assess the influence of leaf-cutting ants (Atta colombica) on nutrient availability in a neotropical rainforest. Twelve nest sites were sampled, including active nests, recently abandoned nests (<1 year) and long-abandoned nests (>1 year). Waste material discarded by the ants down-slope from the nests contained large concentrations of nitrogen and phosphorus in both total and soluble forms, but decomposed within one year after the nests were abandoned. Despite this, soil under the waste material contained high concentrations of nitrate and ammonium that persisted after the disappearance of the waste, although soluble phosphate returned to background concentrations within one year of nest abandonment. Fine roots were more abundant in soil under waste than control soils up to one year after nest abandonment, but were not significantly different for older sites. In contrast to the waste dumps, soil above the underground nest chambers consistently contained lower nutrient concentrations than control soils, although this was not statistically significant. We conclude that the 'islands of fertility' created by leaf-cutting ants provide a nutritional benefit to nearby plants for less than one year after nest abandonment in the moist tropical environment of Barro Colorado Island. Published by Elsevier Ltd.

Relationship Between Population Size and Symbiont Fungus Culture Volume in Colonies of Acromyrmex balzani (Hymenoptera: Formicidae)

In order to quantify the population of Acromyrmex balzani Emery, 1890 nests and to verify whether the population dynamic of the colony is correlated with the symbiont fungus volume, the principal energy source of the colony, five nests located in grassland areas were evaluated. The nests were sprayed with neutral talcum powder to improve visualization and digging. The symbiont fungus and the entire population existent in the chambers were collected. The mean fungus volume and total nest population in excavated nests were, respectively, 74.76 ml and 1,095 individuals. Simple linear correlation analysis verified that the fungus volume grew proportionally to the number of individuals. Despite the correlation between fungus volume and population dynamic of colonies, the factors that determine this relationship are little known since other microorganisms live in association with the colony.

Efficiency and soil contamination during underground application of insecticides: control of leaf-cutting ants with thermal foggers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The nest architecture of the ant, Pheidole oxyops Forel, 1908 (Hymenoptera : Formicidae)

Pheidole oxyops builds subterranean nests, with an external architecture that is distinctive and easily recognizable by its wide and specific entrance hole, measuring up to 12.2 cm in diameter, denoting a pitfall-trap. In order to study the nests'internal architecture, seven nests were excavated; four were identified with neutral talc, while the others were cast in cement and then excavated. Measurements were made in order to gain a better understanding of their structures, and a photographic documentation was obtained as well. The excavations revealed that the nests are perpendicular relative to the ground, beginning with a cylindrical channel with a mean length of 13.5 cm, containing irregular formations, and whose diameter becomes progressively narrower until the first chamber is formed. As the channel continues, dish-like chambers appear, interconnected by channels that become progressively narrower and longer, while the chambers are arranged at greater distances from each other as nest depth increases. Both channels and chambers are located on the vertical projection of the entrance hole. Nests may reach a depth of up to 5.09 m, with a number of chambers ranging between 4 and 14.

Nest Digging by Leaf-Cutting Ants: Effect of Group Size and Functional Structures.

Leaf-cutting ant workers dig underground chambers, for housing their symbiotic fungus, interconnected by a vast quantity of tunnels whose function is to permit the entrance of food (leaves), gaseous exchanges, andmovement of workers, offspring, and the queen. Digging is a task executed by a group of workers, but little is known about the group effect and group-constructed functional structures. Thus, we analyzed the structures formed by worker groups (5, 10, 20, and 40 individuals) of the leaf-cutting ant, Atta sexdens rubropilosa, for 2 days of excavation. The digging arena was the same for the 4 groups, with each group corresponding to a different density. Our results verified a pattern of tunneling by the workers, but no chamber was constructed. The group effect is well known, since the 40-worker group dug significantly more than the groups of 5, 10, and 20. These groups did not differ statistically from each other. Analysis of load/worker verified that workers of the smallest group carried the greatest load. Our paper demonstrates the group effect on the digging of nests, namely, that excavation is proportional to group size, but without emergence of a functional structure such as a chamber.

Substrate distribution in fungus chambers in nests of Atta bisphaerica Forel, 1908 (Hym., Formicidae)

Substrate distribution was studied in three adult colonies of the leaf-cutting ant Atta bisphaerica Forel, 1908 using dye. Some supply holes were mapped using baits made from small plastic straws impregnated with citric pulp. Two holes, equidistant from one another, were then selected in each nest. The colonies were excavated completely 24 h after bait placement. During excavation, fungus chambers were checked for dye. We observed that the dyed baits were distributed in all sectors and at all depths regardless of where the baits had been placed. This supported the hypothesis that toxic baits placed in a single supply hole are uniformly distributed throughout the colony.

Nest architecture and population dynamics of the Ponerinae ant, Ectatomma opaciventre Roger (Hymenoptera : Formicidae)

Eleven nests of Ectatomma opaciventre were collected from January to December, 1994, in Rio Claro, SP, southeastern Brazil. This species excavates their nests up to 68 cm deep, containing 3, 4 or 5 chambers. The hole of entrance has a chimney-like rigid structure, with up to 2/5 cm high. The most numerous colonies were found in January and February, with 47 and 62 adult ants, respectively. The quantity of individuals decreased from March, being observed colonies with only 9 adult ants in June and July. The colony population increased again since September. Reproductive forms (winged ants) were observed between October and February. We did not observed immature stages in July, but they were numerous between September and March. There was a significant correlation between the number of colony individuals and temperature, but not between the number of colony individuals and relative humidity and rainfall. E. opaciventre is a species of hunter ants which have not an efficient recruitment system for food collecting, consequently their colonies are small due to the scarcity of food resources during the colder and dry months.

Nest architecture of Pachycondyla striata Fr. Smith, 1858 (Formicidae, Ponerinae)

Nine nests of Pachycondyla striata Fr. Smith, 1858 were excavated between 2006 and 2007 at the UNESP university campus in Rio Claro, SP, southeastern Brazil. The P. striata population was larger in the two nests excavated in the months of August and November, 2006. The nests of this species are simple and poorly elaborated, with chambers and tunnels close to the ground surface. P. striata places the pupae in chambers isolated from the other individuals. The lack of chambers with the specific purpose of conditioning food and garbage underscores the simplicity of these nests.

Nest architecture of the leaf-cutting ant Acromyrmex rugosus rugosus

The prominent nests mounds of many ant species are one of the most obvious signs of their presence, yet the subterranean architecture of nests is often poorly known. The present work aimed to establish the external and internal structure of nests of a species of leaf-cutting ant, Acromyrmex rugosus rugosus, by either marking the interior of nests with talcum powder, or forming casts with cement. Twelve nests were excavated and surveyed, with eight being marked with talcum powder and four cast with cement. The external and internal structure of the nests was highly variable. The largest and smallest nests had mound areas of 9.89 m(2) and 0.01 m(2) respectively. The number of chambers found ranged from I to 26, with maximum dimensions of between 6 and 70 cm. Chambers were found close to the soil surface (6 cm) down to a maximum depth of 3.75 m. In addition to chambers containing fungus garden, some chambers were found to be empty, filled with soil or filled with waste, the first time this has been recorded in a species of Acromyrmex. The nests of A. rugosus rugosus appear to be unusually complex for the genus, containing a diversity of irregular chambers and tunnels.

Nest architecture of Atta laevigata (F. Smith, 1858) (Hymenoptera : Formicidae)

The internal structure of three nests of Atta laevigata was studied in Botucatu city, São Paulo State, Brazil. Two nests were excavated through the opening of trenches and one was cement-moulded to enable a better view of the internal structures. The three nests presented a similar structure, with the depths and number of chambers varying as a function of the loose soil area of the nests. The number of chambers ranged from 1149 to 7864, reaching as deep as 7 m underground. Chamber volume ranged from 0.03 to 511. The foraging tunnels extended as far as 70m from the loose soil region. The nests of this species are the deepest within the genus Atta and have the highest number of chambers.

Nest architecture and population dynamics of the ponerine ant Ectatomma edentatum (Hymenoptera, Formicidae)

Twelve nests of Ectatomma edentatum (Hymenoptera, Formicidae) were collected from January to December 1996, in Rio Claro, SP, southeastern Brazil. This species excavates their nests up to 1, 10m deep, containing 2, 3, or 4 chambers with an entrance hole of up to 5mm diameter. Colonies with 104, 79, and 82 adult ants respectively were found in February, October, and November. These numbers decreased from March. Colonies with 21 and 16 adult ants were observed in May and July. The colonies' populations increased again in August. Immature stages were not seen January, February, and July, but there were many between March-April and September-November. There was no significant correlation between the number of individuals per colony and temperature or between the number of colonies and relative humidity and rainfall.

Queen lipid content and nest growth in the leaf cutting ant (Atta sexdens rubropilosa) (Hymenoptera: Formicidae)

The relationship between the queens' lipid content and nest growth (population size, biomass and nest architecture) was studied from founding up to 1 year. Nests aged 3, 4, 5, 6, 9 and 12 months were dug in the field, and their dimensions were measured. The ant nest population and fungus garden was also collected. The sample was taken to the laboratory where we counted the worker population and weighed the biomass (fungus plus offspring) and queens. Queens were separated for the determination of lipids. The lipid content in the bodies of queens decreased in the first months, then stabilized (at 4-6 months) before increasing in months 9 and 12. Nest biomass (symbiotic fungus and offspring) and worker population increased over time. The structural growth of the nests was observed by excavating around them. Initially nests (3 months old) had one chamber at an average depth of 15 cm. By 1 year, the nests had three or four deep chambers, and were about 3-4 m deep. Our study contributes to knowledge of the dynamics of the energy-reserve expenditure by queens during colony founding and colony development for up to 1 year. © 2013 Copyright Taylor and Francis Group, LLC.

Interaction and behavior of virgin and physogastric queens in three Meliponini species (Hymenoptera, Apidae)

We studied the behavior of virgin queens of the stingless bee species Schwarziana quadripunctata, Paratrigona lineata and Tetragona clavipes, investigating internal nest activities, including the cell provisioning and oviposition process. We made direct observation of queen behavior, with the aid of video filming. Forty-four virgin queens of S. quadripunctata were observed; one was larger and more attractive than the others. Miniature queens were more abundant than normal-size queens; both were found in prison chambers. Agonistic behavior between virgin and physogastric queens of P. lineata was observed during attempts at queen supersedure. After the disappearance of the physogastric queen and the appearance of a virgin queen in T. clavipes nests, the brood cells were sealed with pollen alone, but no egg. In all three species, the presence of one or more virgin queens appeared to make the colonies nervous, even though constant production of virgin queens is vital to the survival of the colony and is part of the colony cycle in these bees.

A molecular phylogeny and the evolution of nest architecture and behavior in Trigona s.s. (Hymenoptera : Apidae : Meliponini)

Stingless bees exhibit extraordinary variation in nest architecture within and among species. To test for phylogenetic association of behavioral traits for species of the Neotropical stingless bee genus Trigona s.s., a phylogenetic hypothesis was generated by combining sequence data of 24 taxa from one mitochondrial (16S rRNA) and four nuclear gene fragments (long-wavelength rhodopsin copy 1 (opsin), elongation factor-1 alpha copy F2, arginine kinase, and 28S rRNA). Fifteen characteristics of the nest architecture were coded and tested for phylogenetic association. Several characters have significant phylogenetic signal, including type of nesting substrate, nest construction material, and hemipterophily, the tending of hemipteroid insects in exchange for sugar excretions. Phylogenetic independent habits encountered in Trigona s.s. include coprophily and necrophagy.