Little Flies Fulfill Big Dreams
by Tierra Layton

It's a bird, it's a plane, it's … Superfly! A South American parasitic fly may be coming to the rescue for many agricultural producers and Oklahomans by helping control the red imported fire ant population.

Fire ants infest more than 318 million acres in the southern United States, where they have become a considerable agricultural pest and a significant health hazard to people and animals, according to the Oklahoma State University Department of Entomology and Plant Pathology.

The U.S. Department of Agriculture's Agricultural Research Service is the lead agency for the Areawide Fire Ant Suppression Program, said Russ Wright, professor and former head of the OSU Department of Entomology and Plant Pathology.

Florida, Mississippi, Oklahoma, South Carolina and Texas work with the USDA-ARS to help with the parasitic fly research and establishment.

"There is a problem with fire ant populations in Oklahoma, and one of the reasons we are releasing the parasitic fly is to aid in control of the fire ants," Wright said. "This has been an ongoing program for four years, and we are starting to get some results from the release of the parasitic fly."

The parasitic fly being released and trying to gain establishment in Oklahoma is a type of Phorid fly called Pseudacteon curvatus. This fly is used because it is a natural enemy of the fire ant. The natural enemy can provide control because it affects only fire ants, not other species. P. curvatus also can improve and extend the effectiveness of insecticide treatments, according to the USDA-ARS.

"We have released two species of the parasitic fly in Bryan County, but the one that over-wintered was the P. curvatus, and it was released in late May and early June of 2004," Wright said. "Wayne Smith, OSU Cooperative Extension Integrated Pest Management educator for Bryan County, has performed and monitored all of the releases in the area."

Wright said the USDA-ARS suppression program has released parasitic flies on two sites: one site is in southern Bryan County, and the other is in northern Bryan County.

"Although Oklahoma has other types of Phorid flies, they are not the kind of flies that will attack the red imported fire ants," Smith said.

"One of the most important concerns with fire ants is the sting that is inflicted onto humans and wildlife," Smith said. "Given the high numbers of ants that attack, the volume of venom is greater than that of other ants found in the United States."

Fire ant venom is composed of alkaloids that are different from other ants and other stinging insects. Other insect venom is high in protein.

"Some people react severely to the fire ant sting and may go into shock, which can lead to death," Smith said. "There are one or two deaths every year related to fire ant stings and that's usually someone who has a medical condition."

In addition, fire ants are known to cause damage to Oklahoma pastures. In pastures, especially hay fields, the fire ants build large mounds of dirt. The large mounds can cause damage to hay equipment.

"In pasture, fire ants are detrimental toward wildlife," Smith said. "Ground-nesting birds and mammals are subject to ant stings on the newborns, which can lead to death. I have personally seen a nest of baby doves killed and have had reports in my office of people who have lost a litter of puppies or kittens killed by the ants. Even birds nesting in trees can have their hatchlings killed by fire ants."

Fire ants make it to the states

Red imported fire ants first came to the United States around 1930. More than 70 years later, there are five times more ants per acre in the United States than in their native land of South America, according to the USDA-ARS. Natural enemies of the fire ants keep most of the South American ants in check.

The red imported fire ant was recorded in parts of Oklahoma as early as 1985. Fire ants have been found in 39 Oklahoma counties as of late summer 2004.

In the past, eight counties in southern Oklahoma have come under federal quarantine, with special requirements for the shipment of certain goods out of those counties, according to the OSU Department of Entomology and Plant Pathology.

Until now, the primary method of controlling fire ants has been to use insecticides. The only way to maintain control has been to apply insecticides two to four times a year at a cost of at least $10 per acre for each treatment; thus, treating all infested land would cost $6 billion to $12 billion a year, according to the USDA-ARS.

 

They’re going into attack mode

Wright said part of the fire ants' control mechanism is to avoid the flies. When parasitic flies are around, fire ants do not forage well.

"The parasitic fly, which if you can imagine is actually only a half to a quarter of the size of the fire ant, stings the ant," Wright said. "It has been kind of interesting to watch the fire ants and parasitic flies interact with one another."

When the fly stings the ant, it is actually laying an egg into the abdomen of the ant. The fly stings the ant through the exoskeleton and into the side of the body.

"The egg goes through its lifecycle as a maggot," Smith said. "The maggot stays in the body of the ant and eventually migrates to the ant's head. While inside the head, it eats the membrane of the ant and the ant's head will eventually fall off."

That is why these flies are sometimes called "decapitating flies" because they cause the ant's head to fall off, Wright said.

"The adult fly emerges from the mouthparts of the ant's head," Smith said. "This process takes between 30 to 40 days to complete. Once the adult fly emerges from the fire ant, it will only live three to five days."

Smith said the parasitic fly can infect up to 200 ants per day, but, realistically, the fly will lay about 100 to 150 eggs in fire ants per day.

 

I’ve never seen a fly like that!

The first step to releasing the parasitic fly in Oklahoma was to get the parasitic fly into the state.

"All of the flies have to come through the USDA facility in Gainesville, Fla.," Wright said. "Right now, we have to send ants to Florida to get infected with this parasitic fly, and then those ants are reintroduced into their original mounds back here in Bryan County, Oklahoma."

Smith has assisted with all of the parasitic fly releases in Bryan County. He started by gathering ants from 112 mounds total from the northern and southern locations in Bryan County.

He said once the ants are infected with the parasitic fly, the process will begin and flies will be seen within 30 to 40 days.

"The flies over-wintered, which is the first time they have done so in this state," Wright said. "We found them at both sites in Bryan County in the early spring of 2005. The parasitic flies also were spotted three to five miles from each of the sites in Bryan County during the first two weeks of July 2005. We continued to look for them all summer. The extreme drought situation made it hard to find them, but they're there."

Wright said in late October and November 2005, the flies were still present near the sites where they were released.

"We are very hopeful that these flies are established and will continue to expand their range," Wright said. "If the flies follow the pattern of releases in Texas and Tennessee, they should expand 10 to 15 miles a year."

Smith said since the flies are established in Oklahoma, the USDA-ARS can try to relocate some of the flies to the surrounding areas of Bryan County.

 

The flies are here to stay

"The parasitic flies are not going to completely control the fire ants, but we've got big hopes for this little fly," Wright said. "Although they will not eradicate the fire ant population, they'll aid in keeping fire ants from foraging, and they'll aid in knocking down the population of fire ants."

Wright said the parasitic flies should make their way across the fire ant range in Oklahoma within four to five years.

The parasitic fly is bringing financial benefits to Oklahoma as well as to the nation.

Areawide suppression using baits and biological controls of fire ants is expected to save more than $4.6 billion a year in fire ant damage in the United States, according to the USDA-ARS.

The parasitic fly is expected to save money, time and resources for Oklahomans. It will reduce the stress for animals and producers by lowering livestock production costs and increasing farm-worker safety. It truly is a Superfly.

 

For more information, visit the USDA-ARS Areawide Fire Ant Suppression Web site at http://fireant.ifas.ufl.edu/ or the USDA Web site at http://www.ars.usda.gov. Or e-mail Wayne Smith at wayne.smith@okstate.edu.