Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: WEDNESDAY, July 25, 1990 TAG: 9007250127
SECTION: NATIONAL/INTERNATIONAL PAGE: A1 EDITION: METRO
SOURCE: PETER H. LEWIS THE NEW YORK TIMES
DATELINE: COLLEGE STATION, TEXAS LENGTH: Long
Government and private researchers have spent hundreds of millions of dollars in unsuccessful efforts to eradicate the ferocious little arthropod, which is no larger than the "G" at the start of this sentence.
Scientists are mapping its mitochondrial DNA and studying its most intimate chemical scents.
Frustrated homeowners spend tens of millions more on the counterattack, with tactics ranging from pesticides to electric prods, even fighting fire ants with fire.
Yet true to its name, Solenopsis invicta, from the Latin for "invincible," has marched through the South like General Sherman.
From its initial pincer-hold in Mobile, Ala., where it arrived on a ship from South America half a century ago, invicta now infests 250 million acres in 11 Southern states.
Researchers say it has just established a successful colony in Santa Barbara, Calif., its first foray into the country's richest agricultural state.
Entomologists say invicta also seems to be undergoing a fundamental evolution in its social system, establishing giant colonies with multiple queens instead of the smaller and more manageable single-queen colonies that had been characteristic.
"It's just a matter of time before we have fire ant infestations in California and Arizona that we cannot control," said Dr. William P.MacKay, a specialist in ant ecology and systematics at the Fire Ant Laboratory at Texas A&M University here. "It's going to go all the way up the West Coast, all the way to Washington State." Colonies have been found as far north as Virginia.
Four confirmed finds of fire ants were made last fall in the Newport News area: on a golf course, in a residential yard, in an industrial park, and at a Jiffy Lube.
All of those colonies have been treated with an improved insecticide, said John Tate, assistant state supervisor with the Virginia Department of Agriculture and Consumer Service's Bureau of Plant Protection. The locations are being monitored and no more fire ant activity has been observed, he said.
Virginia marks the northernmost range for fire ants because they have trouble surviving the colder winters, Tate said. Fire ants moved into southern North Carolina roughly 15 years ago but have spread little since then, he said.
A suspected source of the ants in Tidewater was a shipment of sod brought from Georgia to a city-owned golf course in Hampton.
The ant's inexorable spread has occurred not only in spite of, but partly because of, nearly four decades of determined campaigns to eradicate it with chemical pesticides.
Through it all, the fire ant has thrived because the pesticides destroyed its enemies and paved the way for far larger colonies than had previously existed.
An airborne pesticide assault in the 1960s and '70s, designed to eradicate the ant from American soil, has been described by the Harvard biologist Edward O. Wilson as "the Vietnam of entomology."
And even a more modest attempt to control the ant with pesticide applications on the ground failed to hold the insect in check.
The campaigns backfired, many entomologists say, because the efforts to kill invicta with the chemicals chlordane, heptachlor, dieldrin and mirex were effective only in wiping out the ant's natural enemies, principally other ant species, and parasites, thus making it easier for the ant to spread.
The pesticides also killed birds and other non-target species. Mirex, in particular, left significant residues in human and animal tissues.
Mirex was determined to be a possible human carcinogen in 1977, and the government's aerial spraying was halted in 1978.
In a draft report prepared for the Texas Fire Ant Advisory Board, the state Department of Agriculture estimated that fire ants caused $47 million in crop losses and pest control expenses in the state last year.
The prospect of peaceful coexistence with invicta is hard for many Southerners to accept, especially for those who know its sting, which is often mistakenly referred to as a bite.
The ant does bite, but only to anchor itself to a victim while it stings. Unlike bees, which eviscerate themselves with each sting, the fire ant stings repeatedly with a gusto that belies its diminutive stature.
The bite is sometimes felt as a minor irritation, but the sting is immediately sensed as a burning sensation, worse than a mosquito bite but not as painful as a bee sting.
It is common for people to be stung many times, since the ants are highly aggressive and swarm onto an intruder in seconds. Some victims have reported suffering hundreds of stings.
A sting later results in redness and swelling, and, because invicta injects bacteria along with its alkaloid venom, creates a small pustule on the skin.
The pustule, typically the size of a pinhead, later causes itching, and sometimes the pustules leave small brown scars that last for months.
Fire ant stings are potentially fatal to people who are allergic to bee stings and other venoms.
Ryan Wingard, a 2-year-old in Anderson, Texas, nearly died in May when he was stung by fire ants in his yard. His mother noticed that he was having trouble breathing, and soon Ryan's lips turned blue, his tongue swelled and red blotches appeared on his body.
He was rushed to the hospital and treated for a severe allergic reaction to multiple fire ant stings. For Ryan and many other people in the South, playing or picnicking in the grass is now just a memory.
"I went to Willie Nelson's Fourth of July picnic and watched people popping up like popcorn, slapping their legs," said Dr. Edward Vargo, an entomologist studying fire ants at the University of Texas' Balcones Research Center in Austin.
Vargo noted that the multiple-queen colonies can be elaborate structures that comprise hundreds of mounds covering dozens of acres, allowing worker ants - sterile females - to forage with astonishing efficiency. "Basically, anything that stands still for longer than 15 or 20 seconds is fire ant food," he said.
Food, to a fire ant, is a broad term. Its diet includes everything from insects to germinating crop seeds to the rubber expansion joints on highway bridges. The ants feed day or night, as long as the temperature is 70 to 95 degrees Fahrenheit.
The impact on the environment is especially worrisome to researchers, who note that invicta drives out other ant and insect species, including native fire ants, which are less aggressive.
Increasingly, landowners say the ants are driving off ground-nesting birds, lizards, rabbits and larger wildlife. The Small Animal Clinic in the College of Veterinary Medicine at Texas A&M has treated 28 fawns this year for severe fire ant stings.
Because invicta is omnivorous, it also has some benefits. Invicta attacks corn worms, boll weevils and other costly agricultural pests, and is actually welcomed on cotton and sugar cane fields.
Fire ants do not live by food alone, MacKay at Texas A&M reported. He has determined that the ant is attracted to electrical fields, the stronger the better.
It is common for the ants to swarm on electrical relay switches inside air conditioning units, until their charred bodies cause a short circuit.
Municipal officials throughout Texas report that fire ants are the leading cause of traffic light failures. Telephone companies say the ants can knock out switching devices.
MacKay said the ants have been found in aircraft altimeters, in computers, and even in the electronic gear in boats and submarines.
Yes, the ants are even aquatic at times, stinging people in swimming pools and rivers. In flood conditions hundreds or thousands of workers will form a living raft to carry the queen and her larvae to safety. Some researchers suggest that such living rafts will help carry invicta west.
More commonly, the ants hitchhike in shipments of grass sod, trees and other nursery stock. They also spread as the queens seek new homes after their mysterious nuptial flights.
Only queens and males develop wings, and because fire ants do not mate in captivity, and because it is difficult to observe tiny insects frolicking at 500 to 800 feet in the air, researchers surmise that the mating is airborne.
On the first sunny day following rain, Southerners can see hundreds of winged male fire ants emerge from the soil and ascend on a sexual kamikaze mission.
They fly only once, rising to several hundred feet, where they compete to mate with a flying queen who has summoned them by some unknown chemical signal. Only one will succeed, and then all the males, perhaps exhausted, fall back to Earth to their deaths.
"If they mate they die happy, and if they don't, they die anyway," said Dr. Daniel Clair, an urban pest management specialist with the Texas Department of Agriculture.
The fertilized queen sheds her wings, burrows and either starts a new colony or joins an existing one. She stores the sperm from her nuptial flight, and for the next five or six years produces offspring - often laying her own weight in eggs each day.
Chastened by the failure of pesticides on invicta, researchers are focusing on two areas: chemical growth regulators and biological controls.
Vargo and others are trying to isolate and synthesize the chemical signals, or pheromones, given off by invicta queens. Pheromones are chemicals that act on other individuals, unlike hormones, which act within an individual.
Among the queen pheromones of particular interest to researchers are signals that cause workers to assassinate rival queens and signals that keep immature females from developing sexually. If such pheromones can be developed, they could disrupt communications in the colony and the ants would eventually die.
by CNB