By John Hawkins

MISSISSIPPI STATE -- Flies with larvae that burrow into the skulls of their prey may seem like characters in a science-fiction movie, but the phorid fly is actually one of the newest tools being used to counter the spread of imported fire ant populations in the Southeast.

The phorid fly, a native of South America, is being introduced to Mississippi as part of a new joint project conducted by the U.S. Department of Agriculture and Mississippi State University's Extension Service. The goal is to provide a biological alternative to the use of chemicals in fire ant control.

"Most of the research is currently taking place in Grenada and Clay counties. The project is set to take place over five years and should help determine how effective the flies will be in controlling fire ants, both with traditional chemical baits and without," said James Jarratt, entomology specialist for MSU's Extension Service.

Jarratt is working with James Vogt, USDA research entomologist with the Biological Control of Pests Research Unit in Stoneville. MSU Extension personnel are involved with educating the general public about the flies and assisting in identifying sites for phorid fly releases.

"We rely heavily on Extension personnel to assist with finding and selecting sites for releases, and establishing contact with the appropriate landowners," Vogt said. "As research progresses and we recruit additional fly species for the fight against fire ants, we hope that MSU Extension personnel will assist with releases and with monitoring for establishment of the flies."

Imported fire ants have proven to be major pests since their accidental introduction to North America in the early 1900s. The imported fire ant is also a native to South America and has no natural enemies in the southeastern United States where they have spread freely, crowding out or eliminating many native ant populations.

The three major breeds of the imported fire ant in the Mississippi region are the red imported fire ant, the black imported fire ant and a hybrid mix of the two.

"Our hope is that the introduction of the phorid fly will help to control the red and black imported breeds as well as the hybrid mix," Jarratt said.

Vogt said the phorid flies are deadly enemies of the fire ants, specifically the black imported fire ant and the hybrid.

"These tiny flies attack fire ants that are out of the nest foraging for food, defending the colony or responding to nest disturbances. The female fly quickly injects a single egg into a fire ant worker. When the egg hatches, the maggot migrates to the ant's head where it continues to develop and eventually eats the brain and muscles," Vogt said.

After the ant has died, the head will usually fall off the body.

The fly larva continues to grow and mature inside the head until it is ready to emerge as an adult fly and begin the cycle again.

Jarratt said one benefit of using phorid flies is that their presence has a dual effect on imported fire ant populations. The first, and most direct effect, is the death of the worker ants which serve as hosts for the fly's young. The second, and more subtle effect, is the response the ants have to the mere presence of the flies.

"When the flies are present, they put pressure on the ant mounds that restricts their ability to forage. The lack of food then causes the size and population of the mound to decrease. This adds to the damage already done to the mound population by the eggs of the flies," Jarratt said.

Vogt said the long term goal of the study is to be able to use natural controls, such as the phorid fly, to lower imported fire ant populations. Other natural controls that are being developed and introduced into ant populations in Mississippi include thelohania solenopsae, a microsporidian disease that is specific to the imported fire ants.

"By introducing natural enemies of fire ants that they escaped when they were introduced to the United States, we hope to reduce fire ant population densities to more acceptable levels, similar to those found in South America. The goal is not to eradicate fire ants, as this is probably not feasible," Vogt said.