for National Geographic News
Importing aliens to attack invading aliens may sound like a plot for a science fiction movie, but scientists believe the scheme is the best way to combat Brazilian fire ants that have taken over the southern U.S.
The red imported fire ant (RIFA), scientifically known as Solenopsis invicta, first arrived on U.S. shores over 60 years ago as stowaways aboard cargo ships from South America. Since then they have spread throughout the South, out-competing the native fire ants in their paths.
"RIFA has such high densities relative to its native counterpart and other native ants probably because it has escaped most of its specific natural enemies, mainly pathogens and parasites," said Larry Gilbert, an ecologist at the University of Texas at Austin.
With no natural enemies in the South, RIFAs have been on a rampage. They are stinging to death baby animals born in the fields, posing a health risk to humans, and laying nests in underground circuit boxes, where the ants cause short circuits and fires.
According to researchers with the U.S. Department of Agriculture, the invading ants ring up an estimated 1.2 billion dollars' worth of damage each year in Texas, where the RIFA takeover is particularly fierce.
Gilbert is exploring ways to control the fire ants. One solution that he believes shows promise is importing other insects from Brazilparasitic flies known as phorids. Phorids kill the ants by laying eggs in them.
Fire Ant Control
A female phorid fly hovers over ants at disturbed mounds or as the ants forage along a trail. She selects an individual in which to lay her egg. She then dives in, injects her egg inside the ant, and darts away. The egg develops in the ant's throat, killing the ant in about ten days.
The phorid larva then moves into the ant's head, which falls off. There, the larva develops into a pupa, more closely resembling an adult phorid. About 40 days later the phorid fly emerges into the world from a pile of dead ants.
Although the flies only kill a small fraction of ants this way, the ants seem to be so afraid of the flies that their mere presence is thought to disrupt the ants' foraging behavior. These interruptions slowly reduce the rate at which new RIFA colonies form.
Gilbert likens this process to a caterpillar eating the leaves of an oak tree. While the caterpillar will not kill the oak tree, the loss of leaves means the trees produce fewer acorns. Thus, over time, new oak trees sprout less frequently than do competing trees.
"I view ants in a parallel way and thus anticipate that the impact of phorids mostly likely will be a slow decline of fire ants relative to native ants," Gilbert said.
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