Dye Found Lethal to Medflies : Pests: Color used in Pepto-Bismol and lipstick shows promise for replacing malathion, researchers say. Two more years of study are expected.
A pink dye used to color Pepto-Bismol and lipstick kills Mediterranean fruit flies and shows early promise for eventually replacing the pesticide malathion in California’s costly and controversial war against the crop-destroying pest, federal researchers say.
Separate tests by two U.S. Department of Agriculture scientists show Medflies in Hawaii and Mexican fruit flies in Texas die when exposed to light after feeding on low concentrations of dye mixed with bait. Apparently when the dye catches light energy from the sun, oxygen turns into a destructive form that wipes out cells in the flies’ gastrointestinal tracts.
The findings by entomologists Nicanor Liquido and Robert Mangan are being presented today at a meeting of the Entomological Society of America in Dallas.
Since aerial spraying of malathion--used periodically to combat Medfly infestations in California--has evoked a public uproar for over a decade, discovery of a nontoxic and inexpensive alternative could be a major advance for farmers and agricultural officials.
“This is very encouraging because there is such public demand for more biologically safe and environmentally safe (substances) as well as ones that the public are more comfortable with,” said Liquido, a USDA research entomologist in Hilo, Hawaii.
Still, Liquido warned, “we try not to make a lot of promises” because larger-scale studies, expected to last at least two years, are necessary.
“We would like to be very sure because of the impact of this research on Medfly eradication programs not only in the U.S. but outside the U.S,” he said.
Henry J. Voss, secretary of the California Department of Food and Agriculture, said he was cautiously optimistic about the USDA’s new findings.
In laboratory tests that began in the fall of 1993, 65% of female flies died after they were fed a molasses or corn syrup mixture containing 0.1% of the dye for two days, Liquido said.
About 800 individual flies were fed each of 10 different dye concentrations and then exposed to artificial light.
Also, when a Medfly-infested 10-acre coffee field in Kauai was sprayed 20 times over a period of three months, about 50% fewer Medflies were counted in the treated field than in an untreated field nearby.
Even more encouraging results were reported on a related pest, Mexican fruit flies, during tests in Texas. “The flies have to seek out the bait station (in those trials),” Mangan said. “At least three-fourths of them did so--and died--in the first trials, and we hope to improve on that.”
Liquido said the dye mix, called SureDye, did not injure crops and has no known harmful effects on humans, wildlife or other plants. USDA officials say the dye had undergone rigorous testing required by the Food and Drug Administration before its use as a color additive in consumer products such as antacids and cosmetics.
“It is considered very, very, very safe,” Liquido said.
The dye is the medium-pink shade of hibiscus flowers, and when mixed with the brownish bait, it turns a maroon shade. The mixture, though, should not discolor the landscape when sprayed in an ultra-fine mist, Liquido said.
“California wouldn’t turn pink,” he said. “You wouldn’t even see the mist.”
The USDA will next test the dye mixture on a larger field in Hawaii. Voss said his department has also authorized research in California to resolve questions of whether it will work in the state’s dry climate.
