Science / Medicine : New Tool in Medfly War: Attractant Plus Malathion
Researchers at a U.S. Department of Agriculture laboratory in Hawaii have devised a new way to kill Mediterranean fruit flies that does not require widespread aerial spraying of the pesticide malathion, but three years of testing may be necessary before the approach can be used in Los Angeles.
The technique is based on the use of a new chemical attractant that would lure Medflies to malathion-laced corn syrup that would be placed on telephone poles and in treetops, where humans and animals would not readily come into contact with the pesticide.
The new lure, named Ceralure after the Medfly (Ceratitis capitata), could also be used in the traps now used to detect the presence of Medflies. Because the new attractant lasts much longer than the lure now used in 30,000 traps in the Los Angeles area, the traps could be replaced much less frequently, reducing labor costs involved in monitoring the pest’s presence.
The luring technique, using a different attractant, has already proven itself over the past 20 years in combatting infestations of a Medfly cousin, the Oriental fruit fly. “This has been an ideal approach,” said entomologist Roy T. Cunningham of USDA’s Tropical Fruit and Vegetable Research Laboratory in Hilo, “because it uses very little insecticide, doesn’t inconvenience people--like aerial spraying sometimes can--and kills males fast, before the population gets a chance to build into an outbreak.”
But before the approach can be implemented in Los Angeles, Cunningham and his colleagues will have to show that the new attractant is environmentally safe. They will also have to demonstrate on a small scale, probably in a remote area of Hawaii, that the approach will actually wipe out a Medfly infestation.
Medfly traps now in use contain a USDA-developed attractant called Trimedlure. That compound is unusual because, unlike attractants used for other insects, it is not the insect’s natural sex pheromone. Pheromones are chemicals released into the air by insects and animals to influence the behavior of other members of their species. For pest control, entomologists usually use a sex pheromone released by females to attract males to bait or traps.
Medflies have a sex pheromone, but researchers have not identified all its ingredients and thus have not been able to reproduce it in the laboratory.
Trimedlure is a totally synthetic compound, loosely related to chemicals found in many plants, that is highly attractive to male Medflies. Researchers have no idea, however, why the insects are attracted.
But the chemical has two drawbacks, Cunningham said. One is that it is highly volatile, so that it evaporates from the traps quickly. The second is that large quantities of Trimedlure, unlike the smaller quantities used as lures, actually repulse the Medflies. Baiting the traps therefore requires a delicate balance between having enough attractant present to last for days or weeks without having enough present to repel the flies.
If Trimedlure were to be used in the telephone-pole approach, the poles would have to be resprayed every two to four days, “which is not economically feasible in an area the size of Los Angeles,” Cunningham said.
In the search for a replacement for Trimedlure, chemist Terrence P. McGovern of the USDA’s research laboratory in Beltsville, Md., synthesized hundreds of chemicals and shipped them to Cunningham, who tested their attractiveness to Medflies in the lab.
Cunningham told an American Chemical Society meeting in Honolulu last week that one of the chemicals recently tested, Ceralure, fills the bill: it is chemically similar to Trimedlure and attracts male Medflies, but lasts two to four times longer.
There are still several hurdles researchers must overcome in order to use the lure for fighting Medflies. The first is obtaining more Ceralure. Cunningham has only a few precious ounces of the liquid to experiment with, but McGovern is experimenting with ways to produce larger quantities. Within two or three months, Cunningham said, he hopes to have several liters.
Next, researchers will have to test its toxicity, “which always takes several months,” he noted. No toxicity problems are expected, however, because of the chemical’s similarity to Trimedlure.
While these tests are being conducted, Cunningham will be developing a gel that will contain the lure and the pesticide, probably in a corn syrup base, testing various formulations to see which is most effective.
Finally, they will have to test its efficacy in the field. “If everything went beautifully, I’d say we could be using Ceralure (in Los Angeles) in three years,” Cunningham said.
