Phytochemical characteristics of leaves determine foraging rate of the leaf-cutting ant Atta mexicana (Smith) (Hymenoptera: Formicidae)

Abstract

Atta mexicana is a polyphagous insect that can exploit a wide range of plant species to cultivate its main food source, the symbiotic fungus Leucoagaricus gongylophorus. In the present study, we evaluated the foraging rate of A. mexicana workers among leaves of three favored and three rejected plant species under laboratory conditions. In addition, we conducted a phytochemical characterization of leaves of these six plant species. Ants preferred leaf discs of Rosa × alba, Trema micrantha and Styrax glabrescens, but rejected those of Coffea arabica, Citrus reticulata and Psidium guajava. In a second behavioral experiment using plant extracts, the results suggest that in the case of C. reticulata, rejection was not due chemical composition, but may have been due to different foliar attributes that could modulate the ant’s foraging preferences in this species. Alkaloids, phenols, flavonoids, and tannins were present at different concentrations in all six plant species. Furthermore, C. arabica leaves presented significantly higher concentrations of alkaloids and this species, together with P. guajava, exhibited the highest concentration of phenols. Rejected plant species showed high concentrations of chlorogenic acid, (−)-epicatechin, quercetin-3, 4-di-O-glucoside (in C. arabica); shikimic acid, ellagic acid and (−)-epicatechin (in P. guajava), and scopoletin (in C. reticulata). Some of the identified compounds have been shown to possess antifungal effects and/or to dissuade leaf-cutter ants from defoliation. We discuss the likely implications on foraging on such plant species by A. mexicana, and on the growth of its symbiotic fungus.