Microorganisms are a large and diverse form of life. Many of them live in association with large multicellular organisms, developing symbiotic relations with the host and some have even evolved to form obligate endosymbiosis 1. All Carpenter ants (genus Camponotus) studied hitherto harbour primary endosymbiotic bacteria of the Blochmannia genus. The role of these bacteria in ant nutrition has been demonstrated 2 but the omnivorous diet of these ants lead us to hypothesize that the bacteria might provide additional advantages to their host. In this study, we establish links between Blochmannia, growth of starting new colonies and the host immune response.

Carpenter ants (genus Camponotus ) have mutualistic, endosymbiotic bacteria of the genus Blochmannia whose main contribution to their hosts is alimentary. It was also recently demonstrated that they play a role in improving immune function as well. In this study, we show that treatment with an antibiotic produces a physiological response inducing an increase in both the quantity of cuticular hydrocarbons and in the melanization of the cuticle probably due to a nutritive and immunological deficit. We suggest that this is because it enhances the protection the cuticle provides from desiccation and also from invasions by pathogens and parasites. Nevertheless, the cuticular hydrocarbon profile is not modified by the antibiotic treatment, which indicates that nestmate recognition is not modified.

The grass-cutting antAtta bisphaericais one of the most serious pests in several pastures and crops in Brazil. Fungal diseases are a constant threat to these large societies composed of millions of closely related individuals. We investigated the occurrence of filamentous fungi associated with the antA. bisphaericain a pasture area of Viçosa, Minas Gerais State, Brazil. Several fungi species were isolated from forager ants, and two of them, known as entomopathogenic,Beauveria bassianaandAspergillus ochraceus, were tested against worker ants in the laboratory. The two species were highly virulent, achieving 50 percent worker mortality within 4-5 days. It is the first timeA. ochraceus, a commonly found fungal species, is reported to infectAttaspecies at a high prevalence. Possible uses for the fungus within biological control are discussed.