Cidália Gabriela Santos Marinho

β-eudesmol-induced aggression in the leaf-cutting ant Atta sexdens rubropilosa

Leaf‐cutting ants are highly polyphagous insects, but some plants escape their attack due to the presence of secondary metabolites that are toxic to the ant–fungus symbiosis. Previous studies have demonstrated that the terpenoid β‐eudesmol extracted from Eucalyptus species (Myrtaceae) is responsible for the deleterious behavior in colonies of leaf‐cutting ant species. The objective of this study was to evaluate the effect of β‐eudesmol on workers of the leaf‐cutting ant Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae). This chemical caused behavioral modification in the colonies, leading to mutilation and death of workers. It is suggested that β‐eudesmol interferes with colony nestmate recognition. As a consequence, colony cohesion may be disrupted by β‐eudesmol what could be used as an additional control tactic against this important pest ant.

Impacto de iscas formicidas granuladas sobre a mirmecofauna não-alvo em eucaliptais segundo duas formas de aplicacação

The effect of localized and systematic use of granulated bait for cutting ant control was assessed on a community of non-target ants in eucalyptus in the municipality of Bom Despacho, Minas Gerais State, Brazil. The ants were collected in Winkler traps on three occasions: eight days before bait distribution, eight and sixty days after distribution by removing the mirmecofauna from 50 1-m2 samples of litter. A total of 102 species was collected belonging to six sub-families. The seven most frequent ant species were analyzed in more detail to assess more precisely the consequences of insecticide treatments. The study showed that systematic control caused negative and more prolonged impact on the ant community than localized control.

Riqueza de espécies de formigas edáficas em plantação de eucalipto e em mata secundária nativa

This investigation was conducted to compare the soil ant fauna of an eucalypt plantation to that of a second growth forest; both areas located in the Zona da Mata of Minas Gerais, Brazil. Tuna fish, honey and cracker baits were used to collect ants along a transect and pitfall traps were distributed in central 900 m of each site. A total of 64 species belonging to 26 genera were collected in the 12 weekly samples; 54 species were captured in the forest and 45 in the Eucalypius granais plantation. A total of eight species presented frequencies above 10% in at least one area. Species richness was higher in the second growth forest. Additional studies should be considcred for further generalizations of the results.

Interference of β-eudesmol in nestmate recognition in Atta sexdens rubropilosa (Hymenoptera: Formicidae)

Leaf-cutter ant species (Atta spp.) are key pests of cultivated crops in the Neotropics, and recent studies have demonstrated that workers of Atta spp., particularly of Atta sexdens rubropilosa, exhibit aggressive behavior among nestmates when in contact with the sesquiterpene beta-eudesmol, found in leaves of Eucalyptus maculata. However, the underlying mechanism sparking this behavior pattern has yet to be investigated. This work aimed to elucidate the mechanism by which this substance elicits aggression in workers of A. sexdens rubropilosa. The results, thus obtained, showed that beta-eudesmol is able to modify the chemical composition of the workers cuticle, impairing nestmate recognition, triggering alarm behavior and leading to nestmate aggression.

Impacto das capinas mecânica e química do sub-bosque de Eucalyptus grandis sobre a comunidade de formigas (Hymenoptera: Formicidae)

O efeito das capinas mecânica e quimica do sub-bosque em plantacoes de eucaliptos e as consequencias desses tratamentos sobre a comunidade de formigas foram avaliados no municipio de Bom Despacho, Minas Gerais, Brasil. As formigas foram coletadas com o extrator de Winkler. Coletou-se um total de 86 especies, pertencentes a seis subfamilias. Oito dias apos as capinas, o numero de especies reduziu-se de um quarto para os dois tipos de capina. Sessenta dias apos, o numero de especies tendeu a retornar ao estagio inicial, verificando-se que a eliminacao do sub-bosque causa efeito deleterio imediato, de igual intensidade e de pouca duracao sobre a comunidade de formigas. As razoes das variacoes observadas serao discutidas.

Atratividade de Atta sexdens rubropilosa por plantas de eucalipto atacadas previamente ou não por Thyrinteina arnobia

The induced defense system of plants is activated after the occurrence of damage by a herbivore. The objective of this work was to evaluate whether plants of Eucalyptus grandis previously attacked by larvae of Thyrinteina arnobia become resistant to cutting by the leaf-cutting ant Atta sexdens rubropilosa. There was no significant difference in the lapse of time spent by the workers of this ant before they started cutting plants previously attacked or not. There was significant reduction in the size of leaf fragments cut by the ants. It was concluded that plants previously attacked were less attractive to the leaf cutter due to the activation of their induced defense system.