Extracts of Ageratum conyzoides, Coriandrum sativum and Mentha piperita inhibit the growth of the symbiotic fungus of leaf-cutting ants

Leaf-cutting ants live in symbiosis with the fungus Leucoagaricus gongylophorus (Singer) Möller that grows in their nests. This fungus is the main nutritional source for these ants that provide conditions for its development. Although plant extracts of Ageratum conyzoides L., Coriandrum sativum L. and Mentha piperita L. are known to cause mortality in ants in the laboratory, their effects on L. gongylophorus are still unknown. The aim of the present study was to determine the effects of the A. conyzoides, C. sativum and M. piperita extracts on L. gongylophorus. The biomass of the fungus grown by the leaf-cutting ants was assessed in culture medium with three concentrations (25, 50, and 100 mg/mL) of A. conyzoides, C. sativum and M. piperita extracts. The results showed that all the three extracts inhibited the growth of L. gongylophorus. At concentrations of 25, 50, and 100 mg/mL, the A. conyzoides extract exhibited 81, 93, and 100% reduction in the fungal biomass; the C. sativum extract showed 23, 27, and 100% reduction in the fungal biomass; and the M. piperita extract demonstrated 96, 99, and 100% reduction in the fungal biomass, respectively. Furthermore, the secondary metabolic compounds of these plants were found to have fungistatic and fungicidal properties, similar to that observed in other fungal species. In conclusion, the extracts of A. conyzoides, C. sativum and M. piperita inhibited the growth of L. gongylophorus in the laboratory, and should be further studied for their potential use in baits to control leaf-cutting ants.