March 28, 2006

Fruit Flies Zapped in Nuclear Pest War

By Mica Rosenberg

EL CERINAL, Guatemala -- Every week, Guatemalan scientists blast 2.7 billion fruit flies with radiation to make them sterile in a bizarre nuclear war against one of the world's most destructive farm pests.

The flies, a threat to the fruit and vegetable industry in California and Florida, are then dropped from planes to copulate with fertile females in Guatemala, Mexico and the United States.

Female medflies only mate once in their month-long lives but can lay up to 800 eggs so barren procreation with sterile males denies the chance of life for hundreds of potential offspring.

As a pest control method, it is easier than killing flies, which once they infect a crop can reduce yields by over 50 percent.

The MOSCAMED facility in Guatemala, which has a major medlfy problem, is on the frontline in the fight against the pest. It is the largest of 25 producers of infertile flies in the world.

"The irradiation destroys the male reproductive organs; there's no sperm," explained Oscar Zelaya, the director of MOSCAMED who said the nuclear rays emitted at the plant are about one-tenth the minimum needed to kill a human.

"The female feels satisfied after copulation but it's impossible for her to produce eggs," he said.

At the plant near the town of El Cerinal, the acrid smell of fly pheromones wafts through warehouses where millions of the bugs are bred then heated in a vat.

The female eggs, genetically engineered for sensitivity to temperature, will die at exactly 93 degrees Fahrenheit (34 degrees Celsius) so only the males remain.

They are grown on trays of sugar cane, wheat and yeast, a specialized diet that nourishes the eggs to hatch into larvae.


In a matter of days, thousands of teeming larva will form a cocoon called a pupa which is zapped with nuclear radiation to stunt their sexual development. The flies then hatch sterile.

The medfly originated in sub-Saharan Africa, but in the age of jet planes it can travel from an infested area like Guatemala to the United States within a matter of hours.

Medfly outbreaks are now common all over the world, from Albania to Zambia, but for the United States the biggest threat comes from Mexico and Guatemala where the pest is more common.

"If we don't catch them soon enough then an outbreak could cost us hundreds of millions of dollars," said Tomas Fasulo an insect expert at the University of Florida.

The United States is free of largest-scale medfly infestations but imports the sterile flies to keep the pest's population down.

The U.S. Department of Agriculture orders coordinated fumigations to rid the country of the fly whenever there is sign of an outbreak.

Although smaller than a housefly, the medfly is known for particularly aggressive destruction of citrus, mangoes, pears and other fruits.

Females will lay more than 75 eggs under the skin of a soft, vulnerable fruit. When the larvae hatch, they burrow deep into the fleshy interior of their new home, reducing it to an inedible mass.

The fly then passes from fruit to fruit, tree to tree where one female medfly can lay up to 22 eggs per day and hundreds in her entire lifetime.

That is why the U.S. government helps fund Guatemala's MOSCAMED facility.

The plant exports about 408 million flies a week to the United States and 650 million to Mexico, but more than 70 percent of the bugs from the facility are dropped in Guatemala.

The whole operation is funded jointly by the three governments and MOSCAMED officials say there's no commercial profit in the impotent fly business.

Daily flights release bags of the chilled, irradiated pupa into the wild, but confused farmers who have rarely been told about the program are often surprised by the unusually large number of flies falling from the sky.

"The people would say, 'Before this used to be a clean area," said Ana Gonzalez a biologist who worked in Lachua, an agricultural region in northern Guatemala. "But that was until the planes came and dropped bags full of worms all over our crops."'