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This study describes and quantifies the behavioural acts of two laboratory colonies of Acromyrmex subterraneus brunneus by investigating worker age polyethism. Twenty-nine behavioural acts were recorded during the 19-week observation period. Young individuals performed tasks inside the nest related to brood care and care for the fungus garden, whereas older individuals performed activities outside the nest such as foraging and activities in the waste chamber. The average longevity (±SD) was 108.21 ± 3.30, 109.15 ± 1.92 and 122.71 ± 1.55 days for large, medium and small workers, respectively. The small-sized workers presented a higher probability of reaching older age than large-and medium-sized workers. This study describes task switching according to age polyethism and the relationship of physical and temporal subcastes.

This work was carried out to determine the internal and external structures of Atta bisphaerica (Forel) nests. Six nests were excavated and during excavation, all data referring to chambers and tunnels were recorded. Three nests had been internally cement-moulded, which enabled a better view of the chamber and tunnel structures. Atta bisphaerica nests presented a similar structural pattern, varying only in the number of chambers as a function of external mound area. Chambers were spherical with two communication tunnels. Internal tunnels had an elliptical section, sometimes circular, indirectly linked to chambers through ramifications and directly through short tunnels. Entrance holes were linked to the area of highest chamber concentration by tunnels from the elliptical section, which led to the nest in a radial manner. Knowledge of the colony's three-dimensional architecture permits successful application of chemical control processes, reduces the quantity of product applied, and consequently diminishes costs and environmental damage.

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 1 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.

The larvae of leaf-cutting ants are maintained within the fungus gardens of their colonies and are fed pieces of fungus by the adult workers. However, little else is known about the nature of the worker-larva interaction in these ecologically important ants. To examine whether workers can gauge the needs of individual larvae, we isolated larvae without adult workers for different lengths of time. We then placed workers with the larvae and recorded the type and frequency of the subsequent behaviours of the workers. Workers scraped the mouthparts of larvae, ingested their faecal fl uid, fed them with fungal hyphae, transported them around the fungus garden and, most frequently, licked their bodies. The workers were also observed to 'plant' fungal hyphae on the bodies of larvae. Workers interacted more frequently with larvae that had been isolated without workers than with those that had not, but there was no effect of the length of isolation. The results suggest that the interactions are complex, involving a number of behaviours that probably serve different functions, and that workers are to some extent able to assess the individual needs of larvae.

16Social groups are at particular risk from parasite infection, which is heightened in eusocial

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The objective of this study was to investigate the seasonal change in the pattern of foraging activity in the leaf-cutting ant Atta capiguara and to provide an estimate of the annual herbivory rate of its colonies. We surveyed at least once a month during 12 months, the foraging activity of two colonies located in a pasture of central Brazil. Each survey consisted in counting the number of ants exiting and returning (laden or unladen) to their nests during 10 min every hour during 24 h. The air temperature and relative humidity were noted at the beginning of each survey. Independent of the season, the colonies presented two peaks of foraging activity, one small peak at the beginning of the day and another peak at the end of the day. During the dry season, the diurnal activity ceased almost completely between 10:00 and 16:00. The proportion of ants returning to the nest laden with a leaf fragment was also lower than during the humid season. Activity rhythm depended significantly on both air temperature and humidity: foraging activity peaked when the temperature was around 25°C and relative humidity around 66 %. Based on the statistical model used to describe the activity rhythm, we estimated that over a period of 1 year, the total dry biomass of vegetation collected by the two colonies studied was, respectively, 25.16 kg for the bigger nest, and 11.69 kg for the smaller one, or an equivalent of 104.83-kg and 48.71-kg fresh biomass, respectively.