Absence of the Parasite Escovopsis in Fungus Garden Pellets Carried by Gynes of Atta sexdens

Abstract

Before preparing for the mating flight gynes of leaf-cutting ants (Hymenoptera: Formicidae: Attini) harvest and store in an infrabuccal pocket a small fragment of their fungus gardens. This pellet is the start culture of the mutualistic fungus when mated gynes establish a new colony. The ant fungal cultivar is threatened by the specialized microfungal parasite Escovopsis, which are exclusively associated with the fungus gardens of attine ants. Reports suggest that Escovopsis transmission between colonies is horizontal, i.e. the parasite is transferred from infected to healthy nests. However, such studies analyzed a relatively small number of fungal pellets or were restricted to a few leaf-cutting ant colonies. Here, we carried out a complementary study on the possible vertical transmission of Escovopsis by sampling a large number of fungus pellets from gynes of Atta sexdens L., a leaf-cutting ant species not studied from this perspective. Gynes were collected during the mating flights in 2009 and 2010, and were left in containers upon regurgitation of the fungal pellets. Each pellet was inoculated on potato dextrose agar and incubated at 25°C. Our results indicate that not signs of Escovopsis were found in pellets. On the other hand, the mutualistic cultivar was prevalent in addition to other fungal species that occurred at lower proportions in the fungal pellets. Our study corroborates results of previous work that Escovopsis vertical transmission does not exist or is negligible, and therefore he parasite transmission can be defined as horizontal.