Hongos simbiontes de hormigas cortadoras de hojas del género Acromyrmex en bosques secos del centro de Argentina

Fungi associated with leaf-cutter ants (LCAs) play a fundamental role in Neotropical ecosystems. The association with fungi allows LCAs to be the dominant herbivores and in this way influence ecological processes. In order to know the taxonomic diversity of fungal symbionts associated with LCAs, ten sampling sites were selected corresponding to the Chaqueño Serrano district and the Algarrobo district. Samples of fungi grown by leaf cutter ants were collected, a part of the fungal material was grown in potato agar culture medium with dextrose and another was stored in a CTAB buffer. Subsequently, amplifications of the ITS1, ITS2 and 5.8S ribosomal gene were carried out. A phylogenetic analysis (Maximum Likelihood and Bayesian) was performed with the sequences. Results show that the leaf cutter ants in the sampled region cultivate symbiotic fungi of two well-differentiated phylogenetic clades (known as A and B). The agar cultures showed a slow growth, with development of globose structures named gongylidia that are grouped together forming staphyla (clusters). Among the ants studied, Acromyrmex striatus is associated with fungi from both clades. In the Espinal forest (Algarrobo district) A. striatus was found associated with clade B fungi (Leucocoprinus sp.) and in the Chaco Serrano (Chaqueño Serrano district) with clade A fungi (Leucocoprinus gongylophorus). While Acromyrmex crassispinus and A. heyeri included in the study exclusively cultivate L. gongylophorus from clade A fungi regardless of the region they inhabit. In addition, the first molecular identification of the fungus L. gongylophorus cultivated by Acromyrmex silvestrii is reported.

Inhibition of symbiote fungus of the leaf cutter ant Atta sexdens by secondary metabolites from the bacterium Xenorhabdus szentirmaii associated with entomopathogenic nematodes

ABSTRACT: Leaf-cutter ants (Hymenoptera: Formicidae) have evolved as dominant herbivores on the American continent. These social insects remove the leaves of economically important plant species to maintain their colony’s food reserves, the symbiotic fungus Leucocoprinus gongylophorus, a basidiomycete. Such fungus can be used for applications of fungicide molecules from metabolites generated by symbiont bacteria (Xenorhabdus and Photorhabdus) from entomopathogenic nematodes (Steinernema and Heterorhabditis). Through isolation and multiplication in tryptic soy broth (TSB) medium of the bacteria Xenorhabdus szentirmaii isolated PAM 25, we conducted laboratorial tests using treatments with 10, 25, and 50% of the metabolites obtained in the sixth day of cultivation. The treatments were centrifuged and filtered to generate a supernatant, which was diluted in potato + dextrose + agar (PDA), to verify the consequences of exposure to the fungus L. gongylophorus in Petri dishes. To confirm metabolite efficiency, the control treatments in PDA only and mixed (PDA+TSB) media were conducted simultaneously for 14 days. We observed total inhibition of the symbiont fungus in both the 25 and 50% dilutions during the first days of the tests. Our results support that these metabolites have inhibitory effect on the development of symbiont fungus of leaf-cutter ants.

Toxicity of sesame extracts to the symbiotic fungus of leaf-cutting ants

Extracts of different sesame plant (Sesamum indicum) Linnaeus organs inhibited the in vitro growth of the fungus Leucocoprinus gongylophorus (Möller) (=Rozites gongylophora Möller), which is cultivated by the leaf-cutting ants of the species Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae). The presence of the factor responsible for this inhibition was detected in methanol or chloroform extracts and is constant in the plant.