Colonies of Atta sexdens are found scattered throughout forest floors and fields - anywhere with an appropriate climate and abundant foliage to harvest. Rather than building upward, A. Atta sexdens divides its colony members into four major castes, each differentiated by a range of head widths. Gardener-Nurses: The smallest of the four castes, gardener-nurses have an average head width of 1. Within-nest Generalists: The next size up, they have an average head width of 1.
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Biologia, 3 Depto. Last instar male larvae were found on August 5, in a six-year-old colony with approximately L of fungus garden distributed in 21 pots. Thirty to forty days later, queen larvae started to be seen. The adult sexual forms were comparable in size with those found in the field. Two apparent failed attempts of a nuptial flight were observed during the last week of October, followed by the appearance of dead males and females in the garbage piles of the colony.
Moser stated that at least 7 mm of rain must soak the soil before Atta texana Buckley sexuals engage on mating swarms. In Brazil, several research institutions have maintained Atta nests in laboratory conditions for many years, but there are no reports of the occurrence of winged forms in these colonies to our knowledge.
Autuori reported that colonies of Atta kept in laboratory for many years including a year-old colony never attempted nuptial flight, nor was the appearance of larvae or pupae of reproductive forms ever observed. On the other hand, Acromyrmex colonies kept in the same laboratory performed nuptial flights annually. The author carried out, with no success, many attempts to discover the possible causes preventing alate production, such as varying food quality and quantity and maintaining the nests under constant temperature and humidity levels comparable to those of natural conditions.
The few references about the appearance of reproductive forms in laboratory conditions report the production of a small brood, unlike the production of thousands of sexuals in field colonies. Bass describes the appearance of a small alate brood in a ten-year-old A.
The first colony lasted 12 years, while another collected later lived for nine years without ever producing sexual forms. In December , a colony collected in the field in April about six months after its founding was transferred to a climate-controlled room in the Centro de Estudos de Insetos Sociais of this Institute. Having ample space to forage and increase the number of fungus chambers, this colony grew rapidly in size.
By July , this 5-year-old colony occupied 21 fungus chambers of varying sizes 1. On August 5 of the same year, unusually large larvae were first seen. These larvae were about three times larger in length than those of the largest worker castes.
They were in fact last instar male larvae since male pupae were observed in the nest a few days later. Even larger larvae were seen 30 to 40 days later, followed by the appearance of female pupae. It is worth noting that in early July of the same year, a fungus chamber of this nest was opened in the laboratory for a routine collection of material and no large worker larva was found.
The small larvae present were unusually turgid and plump and their heads seemed to be located more apically on the body than the typical worker larvae.
It is possible that these larvae were initial instars of reproductive castes. During the production of immature stages of reproductive forms, the fungus garden went through changes in its architecture. Unusually large spaces were opened in the fungus sponge in order to accommodate the large larvae.
In late August, hundreds of adult males could be seen in the fungus garden and hundreds of adult winged females could also be seen by early September Fig. These winged forms were compatible in size with ones collected in the field Fig. The number of workers and the foraging activity of the colony seemed to be greatly increased. During this period, the fungus garden developed considerably, taking up all space available for it.
Workers apparently also became more prone to displaying defensive behavior. Small disturbances on the nest that would normally not affect the workers now caused them to aggressively move around with their mandibles open. Brood care activities as well as caring for the adult winged forms specially females were filmed in VHS with mini and microcameras. Posterior analysis showed that larvae, pupae and adult males and females seemed to be cared for with special interest by the workers in the colony.
Dozens of workers were constantly grooming them. Small pieces of fungus sponge were frequently given to the larvae and adult females by the workers. In an attempt to verify if it would be possible for the reproductive forms to take part in a nuptial flight, a new arena was placed outside the building and connected to the nest by a plastic hose so that winged adults would have access to outside the building.
On two occasions while nuptial flights were taking place on the nests in the field, many males of the laboratory colony attempted to leave the nest by flying inside the room.
Later, the males started to gather in the outside arena but apparently did not fly. In the last week of October, body parts of winged forms started to accumulate in the nest's garbage, while pieces of their tegument were seen being carried by the workers. Winged females were seen in the nest until the end of December. The alates mentioned by Bass did not engage in a nuptial flight either.
The observed increase in worker contingent, the unceasing work with brood care and the impressive uptake of symbiotic fungus by the reproductive forms seemed to require a great amount of energy from the colony and the fungus garden went through a short decline period in which there was a significant decline on the amount of fungus garden in the colony.
By February of the following year the nest had already returned to its normal size and level of activity. A second nest, with L of fungus garden, collected in a year before the first nest and maintained in another climate-controlled room under the same conditions, also initiated the production of reproductive forms in the same year.
The first larvae were seen on September 27, 52 days after the first colony. This colony also produced hundreds of winged males and females but unlike the first colony, which only produced normal-sized alates, this colony also produced smaller reproductive forms Fig.
These miniature males and females seem to be similar to the microgyne reported by Jutsum and Cherrett As it happened to the first colony, the fungus garden of the second nest to produce males and females also went through a decline. The fungus garden became progressively smaller, the number of workers decreased and no brood could be seen.
About the same time the larvae of reproductive forms were first noticed, the functional queen was seen walking outside of the fungus chambers on two separate occasions. This fact led us to believe that the queen was not in perfect health. Two attempts were made to substitute the original queen, with no success. Newly-mated queens returning from nuptial flights were put in "queen cages" and placed in the dwindling colony in an attempt to have the workers get accustomed to her and adopt the new queen as it is done in Apis mellifera Linnaeus hives.
Similar frustrated attempts to replace the queen of a large colony in the process of decline after being kept for 15 years were reported by Autuori and Weber After months of decline, the colony was sacrificed. Fifteen larvae and one male pupa of markedly reduced proportions, measuring less than 1 cm, were found in the two remaining fungus chambers. In September , an adult A. While the first laboratory colony was replete with brood of winged forms and small workers, no brood was found in the fungus garden collected from the field colony.
The field nest, however, already presented adult reproductive forms, suggesting that their production in the laboratory colonies was delayed. On the other hand, the nuptial flight only took place on October 27 and 28 warm days immediately after a period of heavy rain in the nest dug in the field as well as in other field nests in the area.
The causes that led these two colonies to produce the reproductive individuals are not clear. Since these were the largest colonies in our facilities, colony size seems to be a very important factor for alate production.
The authors would like to thank Itamar C. Reiss for the maintenance of the ant colonies. Funding was provided by Fapesp and CNPq. Autuori, M. O sauveiro depois da 1 a revoada Atta sexdens rubropilosa Forel, Behaviour of leafcutting ant sexuals Hym.
Organisation und Leben der Ameisen Wissenschaftliche. Verlagsgesellschaft MBH Stuttgart, p. Wilson, The ants. Harvard University Press, Cambridge, Massachusetts, p. Sexuals and a microgyne of Atta cephalotes L. Hymenoptera, Formicidae from laboratory cultures. Flight utilisation in laboratory-reared males of Atta sexdens. Insect Physiol. Mating activities of Atta texana Hymenoptera, Formicidae. Insectes Soc. Gardening ants, the Attines. The American Philosophical Society, Philadelphia, p. All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License.
Services on Demand Journal. Acknowledgments The authors would like to thank Itamar C. Literature Cited Autuori, M. How to cite this article.
Specimen labels. Check data from AntWeb. Travaglin et al. Forager ants search for adequate food sources in nature and, after their discovery, they decide whether the source is suitable or not for the colony.
Atta sexdens Hymenoptera: Formicidae nests are located under higher canopy cover in colombian amazon rainforests. Abstract: Leafcutter ants, Atta and Acromyrmex spp. Some rainforest leafcutter ant species seem to be found in higher densities at forest edges or gaps, which in some cases are actively created by themselves. This implies the presence of a lower than average canopy cover which, in addition to several ant activities, may lead to vegetation diversification during and after colony life.
Atta sexdens is a species of leafcutter ant belonging to the tribe Attini , native to the New World , from the southern United States Texas to northern Argentina. They cut leaves to provide a substrate for the fungus farms which are their principal source of food. Their societies are among the most complex found in social insects. Other Atta species, such as Atta texana , Atta cephalotes and others, have similar behavior and ecology.