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It's one of the greatest entomological success stories of all times and also one of the least well-known peaceful uses of atomic energy: perfection of an effective control for screwworm, Cochliomyia hominivorax (Coquerel), using x-radiation.

Obnoxious and destructive, the screwworm is the only insect known to consume the living flesh of warm-blooded animals. It has caused immeasurable suffering and losses in livestock, wildlife, and even human populations the world over.

In the 1930's ARS scientists Edward F. Knipling and Raymond C. Bushland turned their attention to alternative screwworm control measures. They concluded that reducing or eliminating the insect population would be a better solution than treating the pests topically after entry into hosts via skin wounds, as was then commonly done.

Though World War II's pressing entomological needs intervened, Knipling never gave up thinking about using genetic means to control screwworms. In 1946, he was named chief of the Insects Affecting Man and Animals Division of USDA's Bureau of Entomology and Plant Quarantine. Four years later, colleague Arthur W. Lindquist recommended to Knipling a book by Nobel laureate H. J. Muller titled "Drosophila," which discussed use of radiation to alter the genetic material of insects. Knipling immediately began a correspondence with Muller exploring the possible use of radiation to sterilize screwworms.

Convinced that the approach could work, Knipling reordered priorities to provide funding for Bushland to carry out tests at Kerrville, Texas. Bushland secured the cooperation of a nearby U.S. Army medical unit with suitable x-ray equipment. In just 6 months, it was handily demonstrated that 2,500 to 5,000 roentgens of x-rays would sterilize screwworm pupae without disrupting their adult mating behavior.

Knipling's theory was simple: Fertile females would mate with sterilized males mass-reared in insectaries and released into infested areas. With offspring resulting only from matings with native, unsterilized males, the screwworm population would gradually become insignificant and perhaps disappear.

But could it really work? First, a field test on Sanibel, the 20-square-mile Florida island, confirmed the theory. Though encouraged, scientists knew that a larger test was needed to verify those early findings. By chance, a routine request from a veterinarian from Curacao, Netherlands Antilles, alerted them to the screwworm's presence on the 170-square-mile island. The Dutch government was eager to assist in its elimination.

So a thousand sterile flies per square mile were released each week by airplane. After just three weeks--the length of one screwworm reproductive cycle--about 70 percent of new egg cases found were sterile. After the next 3 weeks of releases, sterility was 84 percent. And by the end of the third 3-week period, very few egg cases were to be found and all were sterile!

The speed with which screwworm eradication was achieved on Curacao demonstrated the great potential of this control method. Since then, strategic deployment of sterile flies has been used effectively in many locales--most recently, northern Africa--to protect vast areas from the horrific screwworm's predations.

Ever the visionary, Knipling believes that the sterile fly technique can be a successful management tool for many other insects of economic importance. "It's just a matter of working out a few more details," he says. He and Bushland were recently honored for their screwworm research by the United Nations' Food and Agriculture Organization in Rome, Italy.--By Linda R. Tokarz, ARS Information Staff.

[NOTE: The The sterile-insect approach eradicated the screwworm from the U.S. in 1966. Since 1991, Mexico and several countries in Central America have been declared free of screwworm: Belize, Guatemala, El Salvador, Honduras and Nicaragua.]

from the FAO article - "The New World Screwworm in Mexico and Central America"

Program Priorities

  • USDA Secretary Sonny Perdue Visits Japan

    May 13, 2019 — U.S. Secretary of Agriculture Sonny Perdue was in Japan as part of a meeting of Western Hemisphere agriculture leaders meeting on the margins of the G-20 Agricultural Ministerial in Niigata, Japan. On Monday, Secretary Perdue stopped to meet with U.S. and Japan trade negotiators in Tokyo.  Secretary Perdue urged Japan to move swiftly to finalize a trade deal with Washington on farm products and other goods, and to recognize that the U.S. is a “premier customer” for Japan.  Secretary Perdue took time to meet with U.S. Ambassador to Japan Bill Hagerty and the U.S. Embassy Team including APHIS-International Services staff.


  • APHIS Opens New Market for U.S. Exports of Used Cooking Oil

    Apr. 30, 2019  APHIS met with officials from the Portuguese Ministry of Animal Health and representatives of the border inspection posts (BIPs) in Lisbon, Portugal. At the last such meeting held in 2014, Portugal informed APHIS they did not allow the import of used cooking oil, and APHIS presented the case for why Portugal should allow the import of used cooking oil intended for the manufacture of biodiesel as allowed by certain other EU Member States. At the April 23 meeting, Portugal verified that they had decided to open the market for used cooking oil from the United States under favorable conditions that do not require government certification. The estimated value of this market accomplishment is $25 million per year.

  • APHIS Meets with Thailand on Animal Health

    Sept. 18, 2019   APHIS met with Thailand’s Department of Livestock and Development (DLD) in Bangkok, Thailand. APHIS and DLD discussed ongoing issues including U.S. turkey meat access, avian influenza regionalization, rendered meals, and inedible beef offal. In 2018, U.S. trade in animal and animal products reached $196 million.

  • U.S. Announces Trade Deal Reached with Japan

    August 25, 2019 On the margins of the G-7 meeting, President Trump announced that the United States and Japan have agreed “in principle” to a bilateral trade deal involving agriculture and digital products. The deal would focus on lowering tariffs on a wide range of agricultural commodities such as beef, pork, ethanol, DDGs, and soymeal. This agreement will aid exporters who seek to compete with exports from other countries who have partnered with Japan through finalized free trade agreements (FTA). 

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