Ants associated with fronds of the tropical bracken fern Pteridium esculentum subsp. arachnoideum

Pteridium is a cosmopolitan genus of ferns that possess nectaries on its fronds (fern leaves), thereby attracting ants. Foliar (or extrafloral) nectaries are nectar-producing glands that are not related to pollination, but rather attract ants and other arthropods. Foliar nectaries are found in 101 fern species, belonging to 11 genera and six families. The aim of the study is to characterize the community of ants that visit the fronds of Pteridium esculentum subsp. arachnoideum, as well as daily and seasonal ant abundance in different frond development stages. The study was conducted in the Atlantic Forest of Rio de Janeiro state, Brazil. Bimonthly collections were established, where 30 expanding fronds and 30 fully expanded fronds were randomly marked. In each 1-hour shift starting at 8:30 am and ending at 5:30 pm, the fronds were observed for the presence of ants. Thirty three ant species were recorded on the Pteridium esculentum subsp. arachnoideum fronds, distributed into six subfamilies and 13 genera. The most abundant species were Solenopsis sp.1 and Ectatomma tuberculatum. Eight ant species were observed foraging the nectaries of tropical bracken fern fronds. Ectatomma tuberculatum has been observed feeding on the nectaries and patrolling the fronds. Ant activity peak was on mid-day during the rainy season. The tropical bracken fern Pteridium esculentum subsp. arachnoideum has a rich (the highest recorded until now on Pteridium species) and diverse ant community on its fronds, mainly on the expanding fronds. The presence of generalist predatory ants (Ectatomma tuberculatum and Solenopsis sp.1) during the entire study period suggests a positive interaction between ants and Pteridium esculentum subsp. arachnoideum.