The tiny ants, about as long as a penny is thick, deliver painful, long-lasting stings. They were reported by a Maui farmer in October 2009 and were found to infest about a half acre of the farm in Waihee, about 3.6 miles north of the city of Wailuku.
Hawaii Department of Agriculture obtained a special permit from the U.S. Environmental Protection Agency to use an experimental ant bait developed by scientist Cas Vanderwoude with the Pacific Cooperative Studies Unit at the University of Hawaii at Manoa.
The poison, Indoxacarb, is not registered for use against little fire ants on fruit trees, although the EPA has labeled it for other uses.
Ants on the ground can be attacked with poison granules, but not little fire ants on trees. The first step, said Vanderwoude, was to develop a sticky vehicle to spread on the trees. He mixed in a protein-flavored substance to attract the ants to his tree bait and worked to make it suitable for Waihee's wet climate.
Until this new bait was developed, there were only ground treatments for little fire ants. The new bait provided treatment in trees and vegetation where little fire ants nest. The area was treated monthly and by February of 2010, no little fire ants were detected at that site.
But only Thursday did the Hawaii Department of Agriculture feel confident enough to announce success in eradicating the ants.
Little fire ant (Photo courtesy Cas Vanderwoude)
"We have been routinely monitoring the area and we are confident that the ants have been eradicated on the property," said Dr. Neil Reimer, manager of HDOA's Plant Pest Control Branch. "It's pretty clear that without the development of the experimental bait, we would not have been able to eradicate this pest so quickly, if at all."
Monitoring will continue for at least another year, said Dr. Reimer.
"The new pest control methods the state deployed were successful in part because the little fire ants were detected early," said Sandra Lee Kunimoto, who chairs the Hawaii Board of Agriculture.
"This incident serves as an example of why early detection is so important if we are to have any chance of eradicating a pest," Kunimoto said. "We need everyone to be on the lookout for potentially invasive species and, most importantly, to report it to us as soon as possible so appropriate action may be taken to minimize the impact to Hawaii's agricultural sector and environment."
Little fire ants first appeared in Hawaii in 1999 on the Big Island. Surveys determined that little fire ants had been on the east side of the island for several years before they were first identified and were widely distributed in the Puna district.
Attention was then focused on controlling the little fire ant populations and preventing them from spreading to uninfested areas on the island and to other islands.
Originally from South America, little fire ants are considered among the world's worst invasive species.
Pale orange in color, the tiny ants measure just 1/16th of an inch long.
Little fire ants are a different species from another type of ant found in Hawaii that is also called a fire ant.
"The red ants are also called Solenopsis geminata or the tropical fire ant," explains Vanderwoude, who serves as a state Department of Agriculture researcher on the Big Island. "It can be confusing because both species have a similar common name - fire ants - but they are very different."
Red ants are much larger than little fire ants, measuring about half as long as a penny. They move quickly while little fire ants move slowly.
Red ants are originally from the southern United States and they are most often found living in nests in lawns and other open spaces.
Little fire ants can produce painful stings and large red welts and may cause blindness in pets. They can build up very large colonies on the ground and in trees and other vegetation and completely overrun a property. They will also freely move into homes.
Any Maui resident who sees little fire ants is encouraged to report the infestation to the state's Pest Hotline at 643-PEST (7378), a toll-free call from all islands.
Vanderwoude has launched the Hawaii Little Fire Ant website where visitors can explore and download information on the control, eradication, and biology of this invasive species.
The successful bait for little fire ants developed by Vanderwoude at the University of Hawaii may prove popular elsewhere around the world. The state agriculture department has hopes of commercializing its approach, working with the manufacturer, DuPont, and the U.S. EPA.
Indoxacarb is designated by the EPA to be a "reduced-risk" pesticide and is considered an organophosphate replacement. It has moderate to low acute and chronic toxicity and does not cause mutagenic, carcinogenic, developmental, or reproductive effects, according to the EPA.
But there are obstacles to overcome before the new bait can be commercialized.
The EPA has approved Indoxacarb as water dispersible granules for use on apples, pears, cabbages, sweet corn, lettuce and fruiting vegetables. Labeling a pesticide for a new use costs many millions of dollars and the EPA wants a separate trial for each new variety of fruit tree the bait would be used on.
The little fire ant is a common ant species throughout northern and central South America, the West Indies, the warmer portions of Mexico and the southeastern United States.
This species is also found in the Galapagos Islands, West Africa (Gabon, Cameroon, and possibly the Republic of Congo and the Democratic Republic of Congo), Melanesia (New Caledonia, Solomon Islands, Vanuatu, and possibly Tuvalu), Polynesia (Wallis and Futuna and Hawaii), and on subtropical Atlantic islands (the Bahamas and Bermuda).
Little fire ants are also a greenhouse pest in more temperate regions, such as England and Canada.
Populations of little fire ants have been found in Los Angeles County, California. And in 2006, this species was discovered in Israel.
Little fire ants nest under leaf debris, rotten limbs, stones, and in the crotches of trees or clumps of grass. Nests are frequently found behind the sheaths of palms or palmettos. Little fire ants are highly adaptable, nesting in both open and shaded areas, seeming to thrive equally well under moist or dry conditions.
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