Activity of sesame leaf extracts against the symbiotic fungus of Atta sexdens L.

Abstract

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.

E fe i t o d e ex t r a t o s n a t u r a i s d e fo l h a s ve ge t a i s em Leucoagaricus gongylophorus (Möller) Singer, (Agaricales: Agaricaceae)

“…Bueno et al (2004), observaram que ninhos iniciais de laboratório, tratados exclusivamente com folhas do gergelim foram drasticamente afetados e que os compostos tóxicos para as formigas estariam concentrados nos extratos dessa planta. Ribeiro et al (1998) relataram que extratos dessa espécie adicionados em meio de cultura, pode causar até 60% de inibição no desenvolvimento in vitro do fungo simbionte.…”

“…O uso de plantas tóxicas sobre o fungo que vive em simbiose com formigas cortadeiras tem sido proposto como um método alternativo de controle (RIBEIRO et al, 1998). Segundo Cantarelli et al (2005), é possível obter novas formas de produtos com ação inseticida partindo da extração de compostos originados de metabólitos secundários presentes em algumas plantas.…”

Comparison of radial growth rate of the mutualistic fungus of Atta sexdens rubropilosa forel in two culture media

“…Leafcutting ants protect the mutualistic fungus from parasites and potentials competitors (7,8), while the fungus is an essential food source for the larvae and queen (17,20). Other ants in the nests have plant sap as an important food source (23 (14,21,22).…”

“…Studies using mutualistic fungi are difficult due to the very slow fungal growth in culture media (15,16,21,22 …”

Toxicity of Substances Isolated from Helietta puberula RE Fr. (Rutaceae) to the Leaf-cutting Ant Atta sexdens L. (Hymenoptera: Formicidae) and the Symbiotic Fungus Leucoagaricus gongylophorus (Singer) Möller

“…and Vismia baccifera (L.) showed toxic effects to Atta cephalotes L. (Hymenoptera: Formicidae) and to its symbiotic fungus. Like these terpenoids isolated from plants, other vegetal species also presented deleterious effects to leaf-cutting ants as well as to symbiotic fungus, for instance Sesamum indicum L. (Bueno et al 1995, Ribeiro et al 1998, Ricinus communis L. (Acácio- Bigi et al 1998, Bigi et al 2004, Ipomoea batatas (L.) (Hebling et al 2000), Canavalia ensiformis (L.) DC (Monteiro et al 1998, Takahashi-Del-Bianco 2002 and more recently for Cedrela fissilis Vell. .…”