Bsi Nutfall
p. 76 · Read in the full issue
Wars Among
Ants And
A FASCINATING little story, showing how the control of the wars between different types of ants may spell the progress or the ruin of an important in dustry, comes from the British Solomon Islands in a report by two scientists, Mr.
B. A. O’Connor (Fiji * Government ento mologist) and Mr. R. Leach (Cambridge School of Agriculture).
For years, BSI planters were troubled by “nutfall” —the premature falling from the palms of unripe coconuts. Then en tomologists discovered that the chief cause is a bug (Amblypelta Cocophaga China). The bug sucks the growing tis sues of a young nut, and either destroys or distorts it.
The patchiness of “nutfall” put other scientists on a hot trail; and, just before World War 11, it was discovered that a yellow tree-ant, Oecaphylla Smaragdina Subnitida, was a deadly enemy of the bug, and either destroyed it, or drove it off.
Where Oecaphylla flourished, there was no “nutfall.”
But that did not explain the patchiness.
Why did Oecaphylla flourish in one place and not in others?
World War II supplied the solution.
While the nations fought, the BSI plan tations were left to themselves, and be came choked with undergrowth and fallen fronds. After the war, the returning planters found that “nutfall” had largely disappeared from certain of their choked and “dirty” plantations. Again, the en tomologists found the answer to the puzzle.
Oecaphylla is a tree-ant. He rarely goes upon the ground. Upon the ground lives his mortal enemy, another kind of ant, Pheidole; and when Oecaphylla had to make the choice between staying on one tree, and going to another tree per medium of Mother Earth, he stayed on the one tree. But when secondary growth, or fallen fronds, or something like that provided an aerial bridge, from one tree to another, Oecaphylla spread rapidly through the plantation, with a corres ponding decrease in the bug population.
The “dirty” plantations of the war period were Nature’s own gift to the tree ant. It was noticed that one Lever plan tation in the Russells, kept clean through the war-years by cattle, was infested by “nutfall,” while adjoining “dirty” planta tions were free from the pest.
So far, so good. It may yet become sound plantation practice to leave some sort of undergrowth for the use of tree ants.
But the story is not finished. It seems that there is still another kind of ant. an even dirtier dog than the Pheidole. This is the ant Iridomyrme Myrmecodiae.
Pheidole lives upon the ground, and only eats Oecaphylla when the latter comes down out of the trees. But Irido etc., lives also in the trees, and he eats the bug destroying Oecaphylla there whenever he can catch him. So, even in “dirty” plan tations, there are patches of “nutfall,” because Oecaphylla is being caught in the trees by Irido.
The entomologists (Messrs Leach and O’Connor) now seem to have the prob lem clearly lined up. They find that they can control or get rid of Pheidole, on the ground, with DDT spray; but what are they to do with his unmentionable cousin, Irido, who lives, like Oecaphylla, in the tree-tops?