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Knipling, Edward Fred

Published onJul 30, 2021
Knipling, Edward Fred

(March 20, 1909 – March 17, 2009)

Quick Facts

Edward Knipling was an entomologist who worked at the USDA and studied parasitic insects that often targeted cotton or farm animals.

1940s. Source:

Edward F. Knipling was born on a small farm in Port Lavaca, Texas. As a boy, he picked cotton (Gossypium species) in fields devastated by the boll weevil (Anthonomus grandis) and tended calves suffering from screwworm (Cochliomyia hominivorax), fly larvae that burrow into and eat flesh. Untreated infestations can be fatal. These experiences taught Knipling the need to control pests, stimulated his interest in the sciences, especially entomology, and spurred him early in life to pursue a career in the agricultural sciences with the aim of helping farmers overcome obstacles.

Knipling received a BS in 1930 and MS in 1932 in entomology from Texas A & M College (now Texas A & M University). While a student, he joined the U.S. Department of Agriculture (USDA) in 1930 as a field assistant in what was then the Bureau of Entomology and Plant Quarantine. Stationed in Mexico, he studied the pink bollworm (Pectinophora gossypiella), another cotton pest. In 1931 the USDA promoted Knipling to junior entomologist in Menard, Texas, where he rekindled his childhood interest in the screwworm, studying its biology in hopes of devising a method to control it.

Being a pest of livestock and humans in the tropics and subtropics, the screwworm had long been studied. Knipling brought to this inquiry an ability to examine an old, seemingly intransigent problem with fresh eyes. He understood what screwworm flies (and insects generally) do well—reproduce rapidly—determining to find a way of stymieing their fertility. In this work, Knipling concentrated on an overlooked aspect of screwworm reproduction, namely that a male mates throughout life whereas a female mates just once. This insight led him to wonder how he might impede her reproduction.

Knipling might have moved quickly toward a solution, but his talents were needed to combat various pests in Illinois, Iowa, and Georgia. In 1940, stationed in Portland, Oregon, he turned away from agriculture to combat mosquitoes in the Pacific Northwest. This work positioned him to undertake a large study of insects and mites that transmit diseases to humans in hopes of protecting U.S. military personnel from such afflictions during World War II. As director of an Orlando, Florida USDA laboratory, Knipling tested dichlorodiphenyltrichloroethane (DDT) and other insecticides against pests that harbor the microbes and microorganisms causing malaria, typhus, plague, and other killers. Winning national and international accolades, Knipling’s lab developed methods of vector and disease control that continue to be used worldwide, especially in the tropics and subtropics.

These duties forced him to investigate the screwworm as a side issue rather than as the priority. In his off hours, Knipling conceived of sterilization as the solution. Knowing that only fertile organisms can produce offspring, he developed mathematical models in the 1940s based on probability to demonstrate that the release of enormous numbers of sterile screwworms into the environment would overwhelm fertile screwworms, outcompeting them for mates. Recalling that males mate throughout life, Knipling decided that if he could sterilize them, they would copulate with many females. But because each female mates only once, every one that coupled with a sterile male would lay infertile eggs. By targeting the male, Knipling could achieve his aim of crippling female reproduction. As a matter of probability, the swamping of screwworm populations with infertile males would cause them to eradicate themselves, which the New York Times Magazine in January 1970 ranked “the single most original thought in the 20th century.” Knipling did some of this work at Iowa State University, earning a PhD in entomology in 1947.

Borrowing the techniques of other scientists, Knipling and colleague Raymond C. Bushland in the 1950s irradiated screwworms. The method was risky because large X-ray doses were necessary, but too much radiation was fatal. Moreover, without an X-ray machine, Knipling and Bushland had to use a San Antonio, Texas’ hospital machine. Through trial and error, the two determined that irradiation of pupae produced adults healthy but impotent. Being healthy, the males could compete with fertile males for mates, as Knipling had envisioned.

At this juncture, Knipling concentrated on calculating how many sterile males would need to be produced to overwhelm their fertile counterparts whereas Bushland labored to develop a method of rearing that number. Learning about their work, the Netherlands invited Knipling in 1954 to test his ideas on its Caribbean island of Curacao, where screwworms were killing goats and dairy cattle. Being an island, Curacao furnished an isolated experiment, allowing Knipling to translate his mathematics into action. Bushland churned out 170,000 sterile males per week in a Florida lab, sending them to Curacao for release into the wild. That year Knipling and Bushland rid Curacao of the screwworm for the first time in history. The pest has never since recrudesced.

Duplicating these successes, Knipling and Bushland eradicated the screwworm from the southeastern United States in 1959, from the entire United States in 1966, and from Mexico in 1991. Efforts in Central America have confined the screwworm no nearer North America than the Panama-Colombia border. The achievement has saved North American stockmen perhaps $1 billion per year. Entomologists have used the technique to control other pests, including the Mediterranean fruit fly in California.

Between 1953 and 1971, Knipling directed the USDA Agricultural Research Service Entomology Research Division. In addition to conquering the screwworm, he developed several techniques to combat the boll weevil, another childhood goal. Using his methods, cotton growers eliminated the weevil from Virginia and North Carolina in 1987, saving their cotton and the environment from costly and damaging pesticides.

Retiring in 1973, Knipling remained with the USDA as a volunteer consultant, publishing numerous articles and two books and urging scientists and farmers to abandon their overreliance on pesticides in favor of ecologically sound practices. “Knip,” as friends called him, was married sixty-six years to Phoebe Hall Knipling, who had a PhD in zoology from Iowa State College. The couple had five children, fourteen grandchildren, and nine great-grandchildren.

Knipling won many honors, including the United Nations Food and Agriculture Organization’s Medal for Agricultural Science in 1991 and General Foods Corporation’s World Food Prize in 1992. He died in Arlington, Virginia.

Selected Sources

Edward Fred Knipling Papers: Screwworm Eradication Program Records, National Agricultural Library, Beltsville, Maryland.

For secondary sources see Perry Adkisson and James Tumlinson, “Edward F. Knipling, 1909-2000,” National Academy of Sciences, Biographical Memoirs, 2003.

“Biographical Sketch,” Edward Fred Knipling Papers: Screwworm Eradication Program Records, National Agricultural Library, Beltsville, Maryland, April 19, 2018.

Eric Nagourney, “Edward Knipling, 90, Enemy of the Dangerous Screwworm,” New York Times, March 27, 2000.

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