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KELLY VIRELLAOur blood-sucking enemies may have met their match in the copepod, a creature that devours mosquito larvae.
Jorge Rey has spent the past two years studying the cat and mouse game between mosquitoes and one of their biggest predators, a tiny creature that at full size is no bigger than a short eyelash.
With West Nile virus spreading nationwide and infecting at least 25 Florida residents this year, the University of Florida professor wanted his research to lead to new ways to kill the blood-sucking insects.
Enter the copepod, a crustacean that spends its short, carnivorous life scavenging for mosquito larvae. When Rey puts a bunch of the copepods into a pool of water where wingless, wormlike mosquito larvae are growing, the copepods devour them. They rip some of the larvae apart with their jaws and swim away without bothering to eat the carcasses, Rey said.
"Sometimes they maim it so it's not going to live and drop it," he said. "We don't know why they behave this way - maybe it's a reflex reaction. Maybe they're just being mean."
Either way, Rey believes this animosity can be harnessed and used as a cheaper, safer and more effective alternative to many pesticides. All mosquitoes hatch in water, and the copepod is one of the most abundant organisms. Florida residents could pick up where nature left off and put copepods into every possible pool of water, especially the small ones where other mosquito predators like birds and fish cannot live, Rey says.
"The ideal situation would be to have a place where a homeowner could go to get a stock of copepods - you go there, you get them, you put them in your pond," Rey said. "This is not going to replace the use of pesticides altogether, but it can cut out the amount you have to use."
Killing mosquitoes with natural agents, including copepods, is an old idea that George O'Meara, president of the Florida Mosquito Control Association, said he likes.
"I still think it's in the developmental stage, but it's research that should be done," he said. "We need to figure out under what type of condition predation would be greatest."
The discovery in the 1960s that the widely used pesticide DDT destroyed bird eggs galvanized scientists' search for natural pesticides. Researchers soon discovered several new mosquito killers, such as BTI, a bacterial by-product that dices the stomachs of larvae.
BTI is the most popular larvicide used in America today, said Joe Conlon, the technical director for the American Mosquito Control Association, a group of academics and pesticide industry leaders.
Copepods could be cheaper than BTI in some situations because BTI has to be reapplied frequently. But Conlon cautioned against widespread application of a new agent like copepods.
"When you start to introduce large numbers of a species into the environment you get unpredictable results," he said. "The moral of the story is you have to know what you're doing." Copepods have been studied as a mosquito pesticide for nearly 20 years, starting at the Centers for Disease Control and Prevention in Atlanta.
The crayfish-like animals are essentially fish food and go through five to seven phases of life before they mature and begin eating mosquito larvae, said Eric Schreiber, an entomologist with the Sarasota County Mosquito Control District, who has also done copepod research.
Early breakthroughs in copepod research indicated the organisms were an effective and relatively inexpensive way to control mosquito larvae that grow in cisterns of drinking water in many poor countries.
Rey and other researchers have advanced the field by experimenting with species of copepods that are native to their habitats, said Greg Thompson, the director of a New Orleans laboratory that grew out of the CDC's early research. There are thousands of species of copepods worldwide, one of which is an intermediate carrier for River Blindness, Thompson said. That's why Rey's and other researchers' efforts to identify safe species are so important, he said.
"It's a lot better if they go through all the work and find the native species and figure out what they eat and how well they work," he said. "That way all we're really doing is introducing them into their native environment."
Rey, a professor of entomology, used to focus on wetland ecology until his colleagues got him interested in bugs. He calls copepods "little eating machines." But he said he could not foresee any problems with widespread human manipulation of the organism.
"You can't say it's impossible," he said. "But I just can't come up with any scenarios where this would cause a problem."
In two years of studies at the Florida Medical Entomology Laboratory in Vero Beach, Rey and Sheila O'Connell, a biological services technician at the laboratory, found that the Macrocyclops albidus species of copepods can kill up to 90 percent of the mosquito larvae in a pool of water. In one 24-hour period, one copepod kills an average of 32 larvae, he said.
Rey's research showed that copepods work well at tire dumps, which breed mosquitoes inside old, discarded tires, where water collects.
Rey and O'Connell put 15 pairs of tires - one with copepods, one without - into the wooded area behind his lab. Every three weeks they returned and found that the tires with copepods had 90 percent less larvae.
Most Florida counties including Hillsborough, Pasco and Citrus, have tire dumps. But many do not regularly spray for mosquitoes. When they do, they spray BTI, a more expensive agent than copepods, or Abate, a more toxic agent than copepods.
The New Orleans mosquito control board sprayed one of the city's tire dumps with copepods once, and seven years later the mosquitoes hadn't returned, Thompson said. "That's a perfect environment and probably something everybody should do," he said.
Still, many area mosquito control officials balked at the idea of using copepods at the dumps or anywhere else.
"Gee, this research has only been going on as long as I've been in the business," said Robert Ward, manager of Polk County's mosquito control division. "But the reality is that it has not proven itself to be commercially viable. There's still no really good method for getting them into tires."
"In order for us to use it, it would have to be developed in a way that's cost competitive with what we already use," said Doug Wassmer, the entomologist for the Pasco County Mosquito Control District. Rey agrees that more research would have to be done before copepods could be widely used, but said that's no reason to dismiss their potential. Instead, he'll experiment with more species of copepods in more habitats.
"I think to really know if this technique will be successful, it's going to have to be tried in a lot of places," he said.