The objective of this work was to study the effect of colony waste on the mortality of workers of Atta sexdens rubropilosa Forel colonies fed with different plant substrates. Eight nests were used; two colonies each were fed with Acalypha wilkesiana Müller.Arg, Ligustrum japonicum Thunb, Eucalyptus urophylla S.T. Blake or a mixture of the three substrates in equal proportions. Irrespective of diet, being kept with waste led to higher mortality. However, workers that were kept in contact with waste produced by colonies fed Acalypha had higher average survival rate and later death when compared with workers from the other treatments. Workers from the Eucalyptus-fed colonies had the lowest survival rate and 50% of them died within four days of exposure to Eucalyptus waste. Trichoderma viride Pers. ex Gray, a fungus garden antagonist, and the entomopathogen Aspergillus flavus Link. ex Gray were present in the colonies supplied with all plants. The largest fungus diversity was verified in the waste of colonies fed Acalypha and the mixture of Acalypha, Ligustrum and Eucalyptus. Therefore, antibiotic properties of Acalypha did not reduce contaminant diversity but apparently minimized effects of pathogenic microorganisms present in the waste such as Asp. flavus. This may explain the highest survival rate of workers in this treatment.
Material brought to midden piles of leaf-cutting ants is considered to be hazardous. It is therefore expected that midden workers should not re-enter the colony, to reduce pathogen transmission. Here, we examined whether the midden workers of Atta sexdens rubropilosa remain confined to the waste compartment and, if not, whether they could perform many different behaviors in the absence of specialized nestmates. Eleven subcolonies received either midden workers or non-midden workers in addition to pupae and 50 mL of fungus garden. Survival, fungal and brood care, foraging and waste manipulation were observed daily until subcolonies death. Subcolonies maintained by midden workers died earlier: average survival times were 13.92 and 22.66 days for midden and non-midden workers, respectively. Midden workers cared for the brood and foraged as non-midden workers did but they were not as efficient in caring for the garden. Activities related to waste manipulation were more frequently performed by midden workers. These results show that midden workers are not a behaviorally rigid caste and retain many labor capabilities being able to leave the waste compartment and perform internal activities in the absence of specialized internal workers.
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