Folia Microbiol. 50 (5), 421–425 (2005) http://www.biomed.cas.cz/mbu/folia/ Variability of Non-Mutualistic Filamentous Fungi Associated with Atta sexdens rubropilosa Nests A. RODRIGUES a , F.C. PAGNOCCA a , M. BACCI Jr. a , M.J.A. HEBLING a , O.C. BUENO a , L.H. PFENNING b a Centro de Estudos de Insetos Sociais, UNESP, 13506-900 Rio Claro, São Paulo, Brazil b Departamento de Fitopatologia, Universidade Federal de Lavras, 37200-000 Lavras, Minas Gerais, Brazil e-mail andrer@rc.unesp.br Received 9 November 2004 Revised version 18 July 2005 ABSTRACT. A survey of the filamentous fungi other than the symbiotic one found in association with Atta sexdens rubropilosa colonies was carried out. Different fungal species (27 taxa) were isolated a few days after treating the workers with toxic baits (sulfluramid; Mirex-S ® ), from 40 laboratory and 20 field nests. Syncephalastrum racemosum (54 %) and Escovopsis weberi (21 %), Trichoderma harzianum (38 %) and Fusarium oxysporum (23 %) were the prevalent species in laboratory and field nests, respectively. Acre- monium kiliense, Acremonium strictum, E. weberi, F. oxysporum, Fusarium solani, Moniliella suaveolens and T. harzianum were found in both nests’ groups. We revealed that many filamentous fungi can co-exist in a dormant state inside the nests of these insects and some of them appear to be tightly associated with this environment. The well-known leaf-cutting ants of the genera Atta and Acromyrmex (Hymenoptera: tribe Attini) live in a symbiotic relationship with the fungus Leucoagaricus gongylophorus (Silva-Pinhati et al. 2004). These specialized ants are unique since they have the ability to cultivate and feed on their partners. Because huge quantities of fresh plant material are cut to maintain the symbiotic fungus, some authors have raised these ants to a pest’s status, mainly in South American countries, where major losses can occur in cultivated areas (Hölldobler and Wilson 1990). In Brazil, the control of these insects has been done with toxic baits con- taining sulfluramid. In addition to these two organisms involved in the symbiosis, it is known that a pool of microorga- nisms can be found in association with the fungus garden of these ants, such as bacteria, yeasts and filamen- tous fungi (Craven et al. 1970; Fisher et al. 1996; Pagnocca et al. 1996; Carreiro et al. 1997). Inter-specific relationships among some members of this microbiota were observed and for some of these microorganisms it is thought that they could help the symbiotic fungus in the degradation of the plant substrate (Bacci et al. 1995; Carreiro 2000; Carreiro et al. 2002) or to protect the ants from infections by entomopathogenic fungi (Santos et al. 2004). Recent findings have shown that the ants’ nests are, at least in relation to the microbial community, less known than previously thought. Thus, two new yeast species were recently described to occur in this envi- ronment – Cryptoccocus haglerorum (Middelhoven et al. 2003) and Sympodiomyces attinorum (Carreiro et al. 2004). In an exciting discovery, Currie et al. (1999a) described a third partner in this relationship, an actinomycete living on the worker’s cuticle. It was found that these bacteria produce unidentified substances that are specifically targeted to the suppression of growth of Escovopsis spp. The latter are ascomycete ana- morphs, parasites of the fungus garden, found in association with the entire phylogenetic distribution of the Attini tribe (Currie et al. 1999b, 2003a). Escovopsis is a genus with striking morphological characteristics with only two species described, E. weberi (Muchovej and Della Lucia 1990) and E. aspergilloides (Seifert et al. 1995). Infections with this parasite can be persistent and can lead to losses of the garden biomass (Cur- rie 2001) and, occasionally, it can overwhelm the fungus garden even in the presence of the workers. There- fore, evidence shows that Escovopsis sp. is the major fungal contaminant inside the nests of the derived atti- nes, such as the leaf-cutting ants (Currie et al. 1999b). Beside Currie’s research, the research of nonmutualistic filamentous fungi in colonies of leaf-cut- ting ants has been overlooked and only a few studies were made in this respect (Möller 1893; Weber 1966; Bass and Cherrett 1994; Fisher et al. 1996). No study is available concerning the prevalence and species diversity of this group of microorganisms in the nests. Therefore, the aim of the present study was to screen filamentous fungi in the field and laboratory nests of the leaf-cutter ant Atta sexdens rubropilosa. In order to