English Version Abstract Architecture of nests of Leaf-cutter ants Acromyrmex (M.) balzani (Emery), specialized in the cutting of gramineae are very common Acromyrmex (Moellerius) in pastures and agricultural crops of the South West of balzani (Formicidae: Bahia, with high density of nests. The objective of this 1 work was to study aspects of nest architecture of A. balzani, Myrmicini: Attini) in pasture located in pastures in the Southwest of Bahia, in order to search for the improvement of pest control strategies. Ten nests located in the cities of Vitoria da Conquista, Katiane Santiago Silva2, Maria Aparecida Itapetinga, Tremedal and Itambé, BA were selected for Castellani3, Luiz Carlos Forti4, Aldenise Alves study. Externally, the area, the volume of loose soil and the Moreira3, Odair Lacerda Lemos3, Rita de Cássia distance between the mount of loose soil and the tower Silva Carneiro5, Camila Rodrigues Khouri3, Ana were evaluated. The excavation was complete, opening Elizabete Lopes Ribeiro6 gutters and cuttings in the soil profile. Afterwards, the measure of the height, width, depth, and the chambers height, regarding to the soil surface and to the coordinates of an orthogonal axis previously established were performed. The area and volume varied from 325 cm2 to 1880 cm2 and from 0.15 L to 5.88 L respectively. The distances between the loose soil mount and the tower varied from 2 to 37 cm. The total number of chambers per nest varied from 3 to 14, predominantly of chambers containing fungus, adult ants, and young forms. The higher concentration of chambers was at the first 30 cm and near the soil mount, but not under its projection. Key words: Attini; chambers; leaf-cutter ants Introduction they need (WILSON, 1971). Genus Acromyrmex has The tribe Attini (Formicidae, Myrmicinae) approximately 63 nominal species (DELLA LUCIA, groups the ants which cultivate fungi and 1993), grouped in two subgenus, Acromyrmex e comprehend approximately 190 species (MAYÉ- Moellerius, being the former of considerable interest, NUNES and JAFFÉ, 1995), divided in 12 genus mainly because the ranges which comprehend this (HOLLDOBLER and WILSON, 1990), of which subgenus generally are specialized in grass cutting 95% of the species are neotropical and only 5% are (FOWLER, 1988). It is noteworthy, for the loss that found in the Neartic Region (MAYAHÉ-NUNES they determine in pasture, the species Acromyrmex and JAFFÉ, 1995). balzani, Acromyrmex landolti, Acromyrmex striatus and Leaf-cutter ants, genus Atta and Acromyrmex, Acromyrmex heyri (FORTI and BOARETTO, 1997). more known as saúvas and quenquéns, respectively, The first two species are very similar considering have wide geographic distribution, appear in all the the morphological, ethological aspects and the American continent, except Canada, some islands in construction of their nests, considering that A. the Center America and Chile (MARICONI, 1970). balzani was inicially described as a subspecies of A. They are considered plagues in agricultural, landolti and, later, raised to the category of species silvicultural and pastoralist areas, since they use by FOWLER (1988). vegetal substrates to the fungi cultivation, with which Injuries caused by leaf-cutting ants in pastures they live in association to obtain part of the food include reduction of the capacity of pasture (FORTI, Received on: 05 jan. 2010. Accepted for publication on: 02 apr. 2010. 1 Financial support: PRODOC/FAPESB,UESB e CNPq. 2 Professor in Vegetal Production, Universidade Estadual de Mato Grosso do Sul (State University of Mato Grosso do Sul) / Unidade Universitária de Aquidauana, Caixa Postal 25, Aquidauana-MS. 3 Professor in Plant Production, Universidade Estadual do Sudoeste da Bahia (State University of the South of Bahia) - UESB, Caixa postal 95, CEP 45083-900, Vitória da Conquista-BA, e-mail: [email protected] 4 Professor in Entomology, Department of Vegetal Production. /FCA – UNESP, Botucatu- SP. 5 Post-graduated in Agronomy (Crop Science), UESB, Vitória da Conquista,BA. 6 Agronomic engineer, DSc. In Entomology; Pesquisa Aplicada & Agrotecnologia v3 n2 Mai.- Ago. 2010 Print-ISSN 1983-6325 (On line) e-ISSN 1984-7548 107 1985; FOWLER et al., 1990; GALLO et al., 2002), 11.4 cm, with maximum depth from 53 to 124 cm, infestation of the pastures by weeds (AMANTE, while PIMENTA et al. (2007) verified that the nests 1967; FOWLER and ROBINSON, 1977), soil of this ant present four or five chambers, always impoverishment, land devaluation and competition superposed with maximum depth of 95.0 cm. with the cattle. Besides that, according to DELLA Several factors interfere in the spatial LUCIA (1993), A. landolti and A. balzani cause distribution of the nests and in aspects of their severe damage since they cut the pasture close to the architecture. In A. landolti nests there were seasonal soil and due to the fact that they carry grass seeds, ranges in the number and depth of chambers, making the formation of pasture difficult. according to what was proved by LAPOINTE et Acromyrmex species present lower nests than al. (1998). saúvas, which are found in high densities, aspects The architecture of the nests and the which make the control difficult and contribute to distribution of substrates in fungi chambers are increase the importance of these ants (ZANETTI aspects which may interfere in the results of et al., 2003). For A. balzani there are registers in leaf-cutter ant control (MOREIRA et al., 2002; literature of 120 nests ha-1 (GONÇALVES, 1967), MOREIRA et al., 2003; MOREIRA et al., 2004 of .058 nests ha-1 in pasture of Panicum laxum and a e b). 2.441 nests ha-1 in areas with predominance of The present work had as objective to study the Cynodon dactylon and Paspalum notatum (MENDES aspects of the architecture of nests of A. balzani in et al., 1992). For the state of Bahia, Brazil, there are pastures of the Southeast region of the State of Bahia, registers of occurrence of A. balzani in nest density Brazil, searching for subsidies for the perfecting of variable from 800 to 900 ha-1 (LEWIS, 1975) and control strategies. from 25 to 1.900 ha-1, with higher values in pastures with predominance of Panicum maximum and of Material and methods Paspalum sp. and reduced densities in pastures of Brachiaria decumbens (SILVA et al., 2003). For the studies, ten nests of A. balzani were Another aspect which influences in the selected in the Southeast region of Bahia, in which efficiency of the techniques of chemical control three (N1, N2 and N3) in Vitória da Conquista (14º of the leaf-cutting ants is the architecture of the 50’ of South latitude and 40º 50’ of West longitude), nests, achieving great structural complexity in the three (N4, N5 and N6) in Itapetinga (15° 15’ of South species of Atta (MOREIRA et al., 2004 a). Atta latitude and 40° 15’ of West longitude), two (N7 and nests can reach 8 m of depth, with more than seven N8) in Itambé (15° 14’ of South latitude and 40° 37’ thousand chambers (MOREIRA et al., 2004 a). of West longitude) and two in Tremendal (N9 and By contrast, Acromyrmex nests are less deep and N10) (14° 58’ of South latitude and 41° 24’ of West with lower number of chambers (GONÇALVES, longitude). 1964; ANDRADE, 1991). A. balzani nests in Before initiating the work, strings were opened, sunny places and in soils with low humidity stretched out forming an orthogonal axis (x, y), used (ANDRADE, 1991), presenting nests characterized for the localization of all the external and internal by a tower built from fragments of straw and other measures of the nest, with point of intersection vegetal waste which protect them. coincident with the tower of straw, following the Close to the towers land mounts are found procedures described by MOREIRA et al. (2003, in a semicircular form and besides it, the waste 2004 a and b). Initially, it was estimated the area of brought from the interior of the nests. According to the mount of loose soil, taking the largest width and GONÇALVES (1961), nests of A. balzani present the highest length; the volume of the loose soil, by from two to four superposed chambers, with 4 to land sampling and stowage in recipients of known 10 cm of diameter, considering that the last rarely volume; and the distance between the tower and the overcomes 60 cm of depth. MENDES et al. (1992) mount of loose soil. found from 3 to 6 chambers, being the fist ones at After the measurement of the external Pesquisa Aplicada & Agrotecnologia v3 n2 Mai.- Ago. 2010 Print-ISSN 1983-6325 (On line) e-ISSN 1984-7548 108 SILVA, K. S. et al. parameters, the nests were completely excavated, minimize the entrance of water in the nests in the opening furrows in the side of the nest and cutting rainy periods of the year (ANTONIALLI-JUNIOR the soil profile following the channels. They were e GIANNOTTI, 1997). marked with neutral talc to facilitate the excavation. The average distance between the orifices of To the characterization of the chambers, it was taken access to the colony, over which it is placed the straw the measures of width, height, length and depth in tower, and the mount of loose soil of A. balzani nests relation to the soil surface and the orthogonal axis x, y. was 13.7 cm, ranging from 2.0 cm to 37.0 cm (Table With the dimensions of the chambers of three nests, 1). The amplitude of variation was slightly superior it was calculated their volume, comparing them to the to the one obtained by ANDRADE (1991), who geometric figures cylinder and ellipsoid, trough the observed distances of 8.0 to 30.0 cm in nests of A.