Energy substrate used by workers of leaf-cutting ants during nest excavation. In this study we aimed to ascertain whether leaf-cutting ant workers lose body reserves (fat or sugars) as a function of nest excavation. For each treatment, we isolated 10 workers of Atta sexdens into two experimental groups, Control (C- without excavation) and Soil (S- with excavation), which were kept for different time intervals (0, 24, 48 or 72 hours), totaling 700 tested workers. We then determined the concentration of soluble carbohydrates and total lipid content in them. The total carbohydrates were determined colorimetrically, based on the reaction between carbohydrates and sulfuric acid-phenol. For determination of lipids, the insects were immersed in organic solvent until they reached a constant weight. Our results showed that carbohydrates are consumed during nest excavation activities. In the experimental groups S24, S48 and S72, there was an average reduction of 5.82 (20.42%), 14.31 (44.96%) and 13.27 (43.96%) µ.mg-1 in soluble sugar when compared with the experimental groups that did not excavate. Furthermore, the lipids were not used during this activity. With respect to dry mass of the workers, their values were C0 = 8%, C24 = 10.4%, C48 = 9.2%, C72 = 10%, S24 = 9.2%, S48 = 8.7% and S72 = 8.5%. Our results show experimentally that the source of energy for nest excavation is carbohydrates, whereas lipids are conserved for other activities.

Formigas cortadoras de folhas são consideradas pragas para a agricultura devido à grande quantidade de material vegetal utilizado por elas para cultivar um fungo simbionte que lhes serve de alimento e enzimas. O mutualismo entre o fungo e as formigas é um ponto a ser explorado quando se considera sua possível aplicação em métodos alternativos para o controle desses insetos. Sabendo-se que algumas plantas são naturalmente resistentes aos insetos fitófagos, alguns produtos naturais (metabólitos secundários) devem ser avaliados em relação às suas propriedades inseticidas e/ou fungicidas. Neste trabalho foram isoladas oito cumarinas de quatro espécies de plantas e o efeito no desenvolvimento do fungo simbionte das formigas cortadeiras Atta sexdens foi determinado. Com exceção da clausarina, todas as outras cumarinas foram inibitórias de 64 µg mL-1 à 80 µg mL-1 sendo que a xantiletina inibiu o fungo na concentração de 25 µg mL-1.

Leaf-cutting ants are known to be a serious pest for agriculture due to the high amounts of vegetal matter from crops used by them in order to cultivate a symbiotic fungus on which they rely for food and enzymes. The mutualism between the fungus and the ants is a point to be explored when alternative methods of control are being thought of. Considering that some plants are naturally resistant to phytophagous insects, some natural products (secondary metabolites) should be evaluated with respect to their insecticide and/or fungicide properties. In this paper we isolated eight coumarins from four different plant species and we determined their effect on the development of the symbiotic fungus of the leaf-cutting ant Atta sexdens. With the exception of clausarin, all the other coumarins were inhibitory from 64 µg mL-1 through 80 µg mL-1 and xanthyletin inhibited the fungus at 25 µg mL-1

Foi observada, pela primeira vez no Brasil, a produção de centenas de formas aladas em formigueiros de Atta sexdens rubropilosa Forel, mantidos em laboratório. Larvas de último instar de machos foram encontradas em 5 de agosto de 2000 em um formigueiro com quase seis anos de fundação, contendo aproximadamente 110 L de esponja de fungo distribuída em 21 panelas. Entre 30 e 40 dias mais tarde apareceram larvas de fêmeas aladas. Os adultos sexuados apresentaram tamanhos compatíveis com os encontrados em formigueiros de campo. Foram observadas duas aparentes tentativas frustradas de revoada na última semana de outubro, após o que começaram a aparecer machos e fêmeas mortos no lixo do formigueiro.

The production of hundreds of reproductive forms of Atta sexdens rubropilosa Forel in nests maintained in laboratory was observed for the first time in Brazil. Last instar male larvae were found on August 5, 2000 in a six-year-old colony with approximately 110 L of fungus garden distributed in 21 pots. Thirty to forty days later, queen larvae started to be seen. The adult sexual forms were comparable in size with those found in the field. Two apparent failed attempts of a nuptial flight were observed during the last week of October, followed by the appearance of dead males and females in the garbage piles of the colony.

O fungo simbionte Leucoagaricus gongylophorus (Möller) Singer, sin. de Rozites gongylophora Möller, cultivado pela formiga cortadeira Atta sexdens L. teve seu desenvolvimento fortemente inibido por frações obtidas das folhas de gergelim, Sesamum indicum L. (Pedaliaceae). Total inibição foi observada na concentração de 2,5 mg/ml, sendo verificada inibição de 50% com algumas frações na concentração de 1,25 mg/ml. A análise cromatográfica do extrato hexânico revelou a ocorrência de uma mistura de ácidos graxos, onde os componentes majoritários foram os ácidos tetradecanóico, hexadecanóico, octadecanóico, icosanóico, docosanóico e 9,12,15 octadecatrienóico. A separação desses compostos durante as várias etapas do fracionamento resultou em perda ou diminuição da atividade inibitória sobre o fungo, indicando que a inibição observada pode ser consequência da ação conjunta de alguns dos compostos presentes nas folhas e não de uma única substância.

The symbiotic fungus Leucoagaricus gongylophorus (Möller) Singer (syn. Rozites gongylophora Möller) cultivated by the leaf-cutting ant Atta sexdens L. had its development strongly inhibited by crude extracts obtained from leaves of sesame, Sesamum indicum L. (Pedaliaceae). With most of the fractions from these extracts total inhibition was observed at 2.5 mg/ml, whereas inhibition of 50% was observed with some fractions at 1.25 mg/ml. Chromatographic analysis of the hexane extract showed that it was composed by a mixture of fatty acids, of which tetradecanoic, hexadecanoic, octadecanoic, icosanoic, docosanoic and 9,12,15 octadecatrienoic acids were the major components. The separation of these compounds during the different steps of purification resulted in no or lower inhibitory effect for most of these fractions, indicating that the inhibitory activity observed could be due to the joint action of these compounds present in the leaf tissue, rather than to the action of a single substance.