To test this hypothesis, she and her colleagues conducted a series of experiments at the Madre Selva Biological Station in the Amazonian rainforest of Loreto, Peru. The research team located 10 devil's gardens for the study, ranging in size from one to 328 D.hirsuta plants.
Two saplings of a common Amazonian tree called Cedrela odorata, or Spanish cedar, were planted inside each garden near the base of a D. hirsuta tree actively patrolled by worker ants. A sticky insect barrier was applied to one cedar sapling to exclude ants, while the other sapling was left untreated. The researchers planted two additional saplings--one treated, one untreated--about 150 feet outside of each garden but within the primary rainforest.
The results were immediate. Worker ants promptly attacked the untreated saplings, injecting a poison called formic acid into the leaves, which began to die within 24 hours. "Most of the leaves on these saplings were lost within five days, and the proportion lost was significantly higher than on ant-excluded saplings," the authors write. On the other hand, cedars treated with Tanglefoot fared well, whether inside or outside devil's gardens.
"These results show that devil's gardens are produced by M. schumanni workers rather than by D. hirsuta allelopathy," the authors conclude.
Domatia
To find out if worker ants only attack non-host plants, the scientists decided to mimic D. hirsuta's hollow stems, called domatia, which are the ants' primary nesting sites. Artificial domatia were constructed out of foil-wrapped test tubes partially filled with cotton. Two cedar saplings, with and without artificial tubes, were planted in devil's gardens near two D. hirsuta saplings, one with and one without domatia. After 24 hours, there was significant leaf death on all of the cedar plants, but none on any D. hirsuta saplings. "We conclude that M. schumanni att
'"/>
Source:Stanford University