Growth and conidiation response of escovopsis weberi (Ascomycota: Hypocreales) against the fungal cultivar of acromyrmex lundii (Hymenoptera: Formicidae)

Abstract

Leaf-cutter ants (Acromyrmex and Atta spp.) exhibit ancient and complex interactionswith the symbiotic fungus Leucoagaricus (Basidiomycetes: Agaricales) from which they feed, and withthe virulent and speciÞc fungus Escovopsis weberi J.J. Muchovej & Della Lucia (Ascomycetes:Hypocreales) that attacks the antsÕ fungal gardens. This system offers a unique opportunity to studypossible avenues for replacing polluting pesticides with a biological control agent against the ants. Weisolated both Leucoagaricus sp. and E. weberi from the gardens of Acromyrmex lundii Gue´ rin-Me´ nevillecolonies and confronted them with each other by growing Leucoagaricus on petri dishes and placinginoculated pieces of agar inoculated with E. weberi at the edges. Here we present growth curves ofLeucoagaricus sp. and E. weberi in the absence of each other, as a baseline to which we compare theeffect of the fungi on each other. As expected, we found a negative effect of E. weberi on the ant cultivarfrom different colonies of A. lundii. E. weberi increased its growth rate, as well as the levels ofconidiation, in the presence of the ant cultivar. We determined that a soluble and diffusible compound,released by the cultivar, triggered, was responsible for, or did both for the increased levels ofconidiation in E. weberi, and that this response was reversible. We discuss why our results areencouraging from a biological control perspective.