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Electronic Pulses Zap Hitchhikers on Citrus

By Ben Hardin


WASHINGTON, Jan. 14, 1999--Microsecond bursts of high-voltage electrical current could be used to kill fruit fly larvae inside exported citrus, providing a possible alternative to fumigating the citrus with methyl bromide, scientists with the Agricultural Research Service say. ARS is the chief research agency of the U.S. Department of Agriculture.

Alternative methods of certifying U.S. citrus as pest-free are needed because of concerns that methyl bromide may deplete the earth’s ozone layer. The fumigant is scheduled to be phased out by 2005.

The discovery that Mexican fruit flies can be controlled with short electric bursts--called pulsed electric fields (PEF)--is the result of teamwork between an ARS scientist and a Ohio State University researcher.

“Research on alternatives to methyl bromide is an example of scientists in different organizations working together on solutions to issues affecting international trade and our farmers’ ability to compete in world markets,” said ARS Administrator Floyd Horn.

ARS is seeking an industrial partner to assess PEF’s effectiveness on a commercial scale.

Equipment limitations have thus far prevented the researchers from assessing PEF’s effect on fruit quality. Also, economic feasibility and efficacy of PEF must be researched thoroughly before the procedure could be approved by USDA’s Animal and Plant Health Inspection Service for citrus certification, said ARS entomologist Guy J. Hallman. “It’s imperative we examine a host of novel approaches. No single technology is expected to completely replace methyl bromide,” said Hallman, at ARS' Kika de la Garza Subtropical Agricultural Research Center in Weslaco, Texas.

The idea of using PEF to zap fruit flies came to Hallman when he read a technical report by Q. Howard Zhang, a food processing engineer at Ohio State University at Columbus. After finding an electrical pulse generator shelved by the National Aeronautic and Space Administration, Zhang used PEF to research inactivation of microbes such as Escherichiacoli in food.

While 25,000-volt pulses were needed to kill E.coli, Hallman and Zhang found that fruit flies succumbed to much lower voltages. Ten 50-microsecond pulses of 9,000 volts were enough to kill all but three percent of fly eggs. Of the few that hatched to become larvae, none survived to adulthood. Larvae proved even more vulnerable, as none exposed to 2,000 volts lived past the pupal stage to adulthood.

More information about the research is available on the World Wide Web at:


Scientific contact: Guy J. Hallman, ARS Kika de la Garza Subtropical Agricultural Research Center, Weslaco, Tex., phone (956) 565-2647, fax (956) 565-6652,