Tropical Ants Detect Differences in Trees

A tropical ant species with keen chemical detection can distinguish between its host tree and plant interlopers – and the ant uses this ability to aggressively protect its host tree to help ensure survival of the ants, a team of Colorado State University researchers has found.

The ant’s ability to detect and respond to its host’s chemical signals is central to maintaining the tight symbiotic relationship, according to the CSU team’s study, published in the May 12 online edition of “Biotropica,” a scientific journal focused on tropical ecosystems.

“The ants are like gardeners, weeding out competitors to their host plant,” said Tiffany Weir, lead author and assistant professor in the CSU Department of Horticulture and Landscape Architecture. “This allows other trees of the same species to grow, allowing the ant colony to expand by gardening their host trees.”

Weir was part of a CSU research team based at Explorer’s Inn, an ecolodge and research station in the Tambopata National Reserve in Peru. Deep in the Peruvian rainforest, the team examined the interconnection between the tropical ant, Pseudomyrmex triplarinus, and the host tree, Triplaris americana.

The research team, led by Jorge Vivanco, a professor in CSU’s Department of Horticulture and Landscape architecture, looked specifically at the chemical signals involved in the symbiotic relationship that allows the ant species to receive shelter and sustenance from the host tree in return for its defensive activity.

“The ants inhabit hollow channels inside the tree and aggressively fight off any invaders, including other plants. Yet how these ants recognize their host tree, compared to other plants, had not been studied,” Weir said. “We found that the ants distinguish between their host trees and encroaching species through recognition of chemicals in the plant’s surface waxes.”

The team used a series of experiments to demonstrate that ants recognize chemical signals embedded in the leaf surface.

Scientists harvested and replanted tropical grasses and ferns near T. americana trees; the ants systematically pruned away the invaders. The researchers then used sewing pins to attach leaves from several trees, including T. americana, to the host trees; the ants distinguished between unrelated tree leaves and those from T. americana and effectively removed leaves from potentially competing trees.

These and other experiments demonstrated the high degree of specificity involved in this particular symbiotic relationship as well as the involvement of a chemical signal in leaf surface waxes that allows ants to accurately distinguish between their host and other plants, Weir said.

The study sheds more light on symbiotic relationships within rainforest ecosystems and could help to inform rainforest conservation efforts, Weir said.

The work was supported by awards to Vivanco from the Fulbright Scholar Program and the John Simon Guggenheim Memorial Foundation. “Plant-Inhabiting Ant Utilizes Chemical Cues for Host Discrimination” is available at

Team collaborators represented Pontifical Catholic University of Peru, Max Planck Institute of Chemical Ecology and the University of Florida.