Mechanisms involved in maintaining colonies of social insects free of pathogens are among the main aspects of interest in the evolutionary biology of this group. For ants, it has been suggested that secretion from the metapleural glands play an important role in colony asepsis. In this study, different worker subcastes of the fungus-growing ant Atta sexdens piriventris Santschi were compared in relation to presence of metapleural secretion during a year. At the same time, the topical activity of the secretion was tested on workers treated with the entomopathogenic fungus Beauveria bassiana (Bals.) Vuillemin. Based on the mean width of the cephalic capsule, six worker subcastes were defined: gardener, minor, media, large, major and soldier. A positive correlation between worker subcaste and metapleural reservoir length was observed. Significant differences for presence of metapleural secretion were found throughout the year among subcastes, except in April, May, July and November. A positive correlation between seasonal mean temperature and presence of the metapleural secretion was observed. High frequencies of infected workers of all subcastes were observed during bioassays with inoculation of B. bassiana, indicating that metapleural secretion has no fungicidal activity against this pathogen. The results suggest that metapleural secretion of workers is not the main mechanism of A. sexdens piriventris colony asepsis.
Insecta; fungus-growing ants; metapleural gland; entomopathogenic fungus; biological control
