The latest threat to tropical rain forests comes from one of its smallest inhabitants: ants.
U biology professor Diane “Dinah” Davidson is in the rain forests of Peru researching them.
Dolichoderine ants, named for their unique chemistry and lack of sting, have been secretly killing trees by indirectly feeding on tree sap. Loss of sap robs the trees of water, carbohydrates and amino acids-all of which are necessary to their survival.
Davidson initiated the study of the ants’ damaging tendencies and is currently researching the ants in Peru, at the Cocha Cashu Biological station, where she has been conducting research for the last 20 years.
It was previously believed ants only fed on other insects. However, Davidson and her colleagues recently discovered the majority feed on excretion from tree-eating insects.
These insects, such as tree-hoppers or scale insects, suck nutrient-rich sap from the trees. Loss of sap, coupled with drought, can result in a tree’s death.
By eating the excretion, or “honeydew,” the ants are indirectly feeding on the tree itself.
The problem may cause far more damage to rain forests than was previously believed, according to a recent statement about Davidson’s study.
This is mostly due to the fact that the ants are not eating the parasitic insects, but are instead protecting them.
The ants protect the tree-eating insects from birds, wasps and flies in order to eat their honeydew.
“This means the sap-suckers can become incredibly abundant,” Davidson said in the statement.
Davidson’s assistant at the U, doctoral student Steven Cook, pointed out the damage does not only affect mature trees.
“Hemipteran trophobionts [Sap-suckers] that are tended by ants are taking a lot of plant resources, thereby decreasing growth rates of the young trees [and] plants.,” he said.
This, Cook says, “may even be retarding ecological succession,” meaning the regeneration of the rain forest may be hindered by the ants.
Davidson and her colleagues studied nitrogen ratios of the ants using mass spectrometers, which weigh atoms and can distinguish rare forms of nitrogen.
They learned that Dolichoderine ants have a lower ratio of nitrogen than carnivorous ants.
In fact, their nitrogen ratios better resembled herbivorous insects.
This led Davidson’s team to believe that the ants were eating something other than dead insects. They then discovered that the ants were feeding on the honeydew of parasitic insects.
The parasitic insects are able to suck sap from the trees through their tiny straw-like mouths. Bacteria inside the insects transform the sap into essential amino acids. Once secreted, this nutrient-rich honeydew sustains the ants.
Although Cook says the extent of the ants’ damage to the rain forests is “not really known,” he said the loss of sap does “slow [tree] growth, and in extreme cases, may kill them.”
It seems the damage caused by these small inhabitants could exceed what was previously believed.
Davidson’s study was recently published in the May 9 issue of Science journal.