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 From the News Desk...Natural predatorby John ReitmanA new weapon could be emerging in the ongoing battle against fire ants. But the answer does not come from a bottle or jug; instead it comes on the wing of a parasitic fly that deposits its eggs into the ant’s body where the larva hatches and develops before popping out, conjuring thoughts of scenes from a science fiction movie. The relationship between parasitizing phorid flies and their natural prey, imported red fire ants, is nothing new. Researchers from the U.S. Department of Agriculture and universities throughout the Southeast have been studying phorid flies and imported red fire ants – both from South America – since the early 1990s. Since 1997, researchers have released four species of the flies in 12 states. To date, they are found in more than half of the fire ant range in the United States, according to the USDA. Current work by researchers at in Texas and Florida could provide even more hope that phorid flies can help naturally control the imported red fire ant population. Until recently, phorid flies released in the United States have attacked fire ants only while they made repairs to disturbed mounds. But the species Pseudacteon obtusus, which was released in 2004 at sites in Florida and Texas, preys upon the ants while they forage for food and water – which occurs with much more regularity than does nest repair. Researchers at Texas A&M University hope Pseudacteon obtusus can help control fire ant populations, first by parasitizing some of then hosts, and second by scaring those who aren’t infected into staying in the mound rather than coming out to search for food and water to support the rest of the colony. The latter behavior was first observed and identified by Don Feener, Ph.D., professor of entomology at the University of Utah.  Nectar feeders, phorid flies only prey upon fire ants to propagate their numbers and are a virtual non-threat to native ant species. Although laying their eggs in fire ants is lethal to the host, the flies won’t replace chemical controls, but rather are viewed by researchers as a means of supplemental control, said Robert Puckett, Ph.D., assistant research scientist at Texas A&M.
Puckett has spent years observing behavior in ants, and says they go into panic mode when phorid flies are active. In fact, they become so sensitized to fly activity that they are reluctant to wander outside the mound to forage for resources. “Nobody expects this to completely control colonies with 100,000 workers. Our expectations are realistic,” Puckett said. “Once the flies are active and the ants are under attack, they spend less time out of their mound doing what ants do. Ants require some amount of nutrients, but if they’re spending time in the mound they can’t collect that. That’s the whole idea.” Much of the early work in phorid fly/fire ant research was conducted by Sanford Porter, Ph.D., research entomologist with the U.S. Department of Agriculture-Agricultural Research Service in Gainesville, Fla., and Larry Gilbert, Ph.D., director of the Brackenridge Field Station at the University of Texas. There are about 20 species of phorid flies in South America that prey upon fire ants, but only a handful of species have been studied in the United States. Pseudacteon tricuspis was released in Florida in 1997. As recently as late 2008, its range had spread to an estimated 270,000 miles, or half the range of imported red fire ants, according to the USDA. Pseudacteon curvatus was released in 2000 in 11 states. This species has spread very quickly, today occupying more than 320,000 square miles. Also released in the U.S. was Pseudacteon litoralis, which has been detected in Alabama. Pseudacteon obtusus is thriving in parts of Texas and Florida since first being released five years ago. “They have plenty of hosts,” Puckett said of the various species of phorid flies. “So their numbers are always growing.” Whether they attack ants that are rebuilding their mound or foraging for food, all phorid flies are attracted by pheromones secreted by their potential hosts. The female fly, about 1 mm in length, carries a clutch of about 200 eggs. She injects a single egg into the thorax of a fire ant worker through a hardened ovipositor capable of compromising the ant’s exoskeleton or the connecting tissue between the host’s head and thorax. Video of the process shows that despite its size, the fly hits the ant with a force capable of knocking the host of its feet. “It stuns them,” Puckett said. “At that point, the ant is doomed.” Like something from a move, the developing larva eventually migrates to the ant’s head, secreting enzymes along the way that weaken the connecting tissue between head and thorax. Within four to seven days the host’s head falls off and the juvenile fly feeds on the liquid inside. Eventually, an adult fly emerges starting the process all over again. The fly has developed the ability to control the ant’s mobility just before it lops off its head, forcing the host to involuntarily wander away from its mound – perhaps by as much as 50 yards, according to researchers. The parasite does this so that it can develop into an adult without being threatened by the rest of the ant colony, Puckett said. “It wouldn’t be a good idea for a soft, vulnerable (fly) larva to be exposed to a colony of 100,000 or 200,000 worker ants,” Puckett said. Video on the USDA-ARS Web site shows the ferocity of this relationship. It is plain to see the erratic behavior the presence of the flies cause in ants and the knockdown force of the egg-depositing process. It also shows that the ant, which is much larger than its predator, is perfectly capable of turning the tables on the fly and killing it if it manages to catch one.  Fire ants are an ongoing problem on golf courses throughout the Southeast and parts of the West, including New Orleans Country Club.
If it rains enough that Mayberry’s crew must skip mowing for a day or two, fire ant mounds emerge quickly in the fairways. “They can build a mound in a couple of hours,” Mayberry said. “They seem to pop up out of nowhere.” Imported red fire ants entered the United States in the 1930s aboard a cargo ship docked in Mobile, Ala. They are much more aggressive than native ant species, including two species of native fire ants. Scientists hope that any control provided by phorid flies not only will help control an unwanted pest, but also will be beneficial for native ant species. Phorid flies prey primarily on imported red fire ants, but on rare occasions might also target native fire ants species. However, the symbiotic relationship that exists between the flies and imported fire ants does not exist with native species. Therefore, flies could not support their own populations by parasitizing native ant species, according to Puckett. Predators that have been observed include spiders and dragonflies and probably purple martens, Puckett said. Conscientious scientists struggle with introducing non-native species of any plant or animal to a new environment for purposes of biological control, and the phorid fly is no different. But after years of study, researchers have deemed the fly to be so non-invasive to other species that introducing them to control imported red fire ants was a risk worth taking. “Any person who works in biological controls, if they don’t ask that question of themselves first, they shouldn’t be doing what they’re doing. Those who did the early research in this field were very conscious of this,” Puckett said. “These flies are very host specific. They are completely honed in on fire ant pheromones. “They are relatively benign, and they are beneficial in a lot of different ways.” Previously unaware of the fly-ant relationship, Mayberry also sees the benefit in a biological control that, according to researchers, is benign to other species. “Anything biological can potentially lessen the amount of chemicals we use,” Mayberry said. “If it works, that would be great.” |
In other news... Study examines spring pre-stress fertility programs Research finds no correlation between biostimulant applications before spring core cultivation and recovery. Posted: 09/02/2010 Read more » Aquatrols, TurfNet present Water Week The series of five Webinars is aimed at helping superintendents manage water and soils more efficiently. Posted: 09/01/2010 Read more » News and people briefs Registration opens soon for Irrigation Show, Briggs & Stratton elects new chairman, FMC taps new director for professional solutions division Posted: 09/01/2010 Read more » GCSAA selects firm in search for new CEO Kansas City-based company will open search process for Mark Woodward's successor in October. Posted: 08/31/2010 Read more » Water foul! Research shows that droppings from non-migratory geese on turf can result in nitrogen runoff into adjacent bodies of water. Posted: 08/26/2010 Read more » Complete news index » |
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