Mycoparasites isolated from Acromyrmex spp and Atta spp colonies: antagonism and mycoparasitism

NORMA GOROSITO; MATIAS CAFARO; DEBORAH COLMAN; PATRICIA FOLGARAIT

Congreso; VI Congreso Argentino de Microbiología General. Sociedad Argentina de Microbiología General (SAMIGE); 2009

Leaf-cutter ants belong to the New World, primarily distributed in the Neotropical region. This ant species have an obligate relationship with the fungus Leucoagaricus spp. (Basidiomycotina), which the ants cultivate to feed from it the structures called gongylidia. To cultivate the fungus the ants collect fresh material from a variety of plant species. The symbiotic relationship between leaf cutter ants and Leucoagaricus is threatened by a specific mycoparasite: Escovopsis spp (Ascomycotina: Hypocreales). This mycoparasite can completely destroy the colonies of the leaf cutters by parasitizing their food. The ant species that belong to the genera Atta and Acromyrmex are considered pests due to the high density they achieve and enormous amount of fresh biomass they cut. Usually these ant species are controlled with pesticides which can kill the ants, but also non target species, besides being toxic to humans and the environment. An alternative to reduce the leaf cutter ant numbers is the biocontrol. Our goals were: 1) to evaluate the performance of different strains of Escovopsis and Trichoderma against the symbiotic fungus f the leafcutter ant, and 2) to study the possible antagonism between two mycoparasites: Escovopsis and Trichoderma, which might be used for the biocontrol of these ants. To achieve our goals we used Leucoagaricus, Escovopsis and Trichoderma isolated from Acromyrmex heyeri, Escovopsis and Trichoderma isolated from A. lobicornis, and Escovopsis isolated from Atta vollenweideri. We challenged the three Escovopsis and two Thrichoderma strains against the Leucoagaricus, and two Escovopsis with the two Trichoderma strains. For the challenges we used PDA petri dishes, and the organisms were plated on them. In the challenges Escovopsis-Leucoagaricus, and Trichoderma -Leucoagaricus, Escovopsis and Trichoderma had overgrown the cultivar completely. In the challenges Trichoderma-Escovopsis, Thrichoderma had a higher rate of growth and overgrew the Escovopsis 100% of the times. Trichoderma was never negatively affected by the presence of Escovopsis, and in fact grew as fast as its control. Our results highlighted the negative effect of the mycoparasitism by Escovopsis and Trichoderma against the Leucoagaricus. Finally, we can conclude that in biological control programs of leafcutter ants, it will not be desirable to apply Escovopsis and Trichoderma simultaneously, due to the antagonistic effects found in this work.