Biodiversity Pays

Biodiversity Pays: Study Shows Shade Trees Shelter Coffee from Ant Damage

Editors please note: Photos and video of the ants in action are available by contacting the authors.

MOSCOW—Damage by leaf-cutting ants is more extensive in coffee-only plantations than in those with shade trees intermixed.

The conclusion: ants avoid coffee when they can, a team of University of Idaho scientists found during studies in Costa Rica.

Proponents of plantations of intermixed coffee and shade trees say they provide better habitat for birds and other wildlife. The University of Idaho study by Edgar H. Varón and colleagues provided further evidence that the increased biodiversity in shaded coffee plantations can provide benefits, the authors say.

The team reported its findings in the latest issue of the journal Agricultural and Forest Entomology.

The evidence is strong that damage to coffee by leaf-cutting ants is greatest in coffee-only plantations, according to Sanford Eigenbrode, a University of Idaho Professor and Chair of the Division of Entomology, who oversaw Varon’s research and studies to earn a doctorate.

“The ants can be significant pests on citrus, coffee and other crops. They are capable of defoliating small trees overnight,” Eigenbrode said.

Individual ants carve a neat arch into a leaf, carrying the piece back to its nest. Workers there grow a specific fungus that thrives on the harvested leaf pieces. The fungus feeds the colony’s queen and her larvae.

“It’s been called nature’s example of agriculture,” said Nilsa Bosque-Pérez, the UI entomology professor who directs an international, interdisciplinary program in graduate education funded by the Integrative Graduate Research and Education Traineeship Program (IGERT) program of the National Science Foundation.

She and Luko Hilje of Costa Rica’s Tropical Agricultural Research and Higher Education Center also served as co-authors on the publication.

The IGERT project includes students working in Costa Rica and Idaho to understand how biodiversity conservation and sustainable agriculture can be complimentary.

In Idaho, for example, a team of doctoral students in the program is studying the interplay of insects from remnants of native Palouse prairie, the original ecosystem covering southeastern Washington State and adjacent Idaho, and cultivated fields.

Varon’s work was part of a larger interdisciplinary team effort assessing the potential role of coffee agroforestry systems for increasing environmental services, including pest management, conservation of biodiversity and hydrological services, Bosque-Pérez said.

In Costa Rican coffee-only plantations, Varon showed 40 percent of the plant material carried back to the ant nest was from coffee trees. In plantations shaded by the poro tree, ants preferred it and harvested less coffee.

In farms with complex shade from multiple tree species, the percentage of coffee leaves carried back to the nest dropped to just one percent.

The ant damage can pose a significant cost in coffee-only plantations grown without shade, although the yields overall in so-called ‘sun coffee’ tend to be higher. The economic analysis of pest control and other costs of sun- vs. shade-grown coffee were not part of the study, Eigenbrode said.

The leaf cutting ants do serve an important environmental function, Bosque-Pérez noted. They are among the most important recyclers of plant material in the Costa Rican lowland humid forests and elsewhere in Central America.

In all, 39 species of ants have evolved that harvest living plants to grow one specific fungus as the only food eaten by their larvae. The adult ants that harvest the plants primarily feed on sap.

In August, Varon was the first graduate of the joint doctoral program between the University of Idaho and Costa Rica’s Tropical Agricultural Research and Higher Education Center.

Founded in 2000, this program offers opportunities for doctoral students to take coursework towards their degrees in Idaho, then live and conduct their research on agriculture and natural resources, including sustainable production and biodiversity conservation in the American tropics. So far 15 students have participated and five have earned their degrees through this unique program.