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United States Department of Agriculture

Agricultural Research Service

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The Life and Vision of Edward F. Knipling Concerning the Eradication of the Screwworm
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Presented by Dr. E. B. Knipling
  Slide featuring photograph of Dr. E.F. Knipling

Good afternoon. I am delighted to be here on behalf of the U.S. Department of Agriculture on this important anniversary celebration. It is also a great honor on behalf of the entire Knipling family and to the memory of my father, Edward F. Knipling.
Today, I’d like to tell you a little about my father, his values and vision, and what I believe to be his legacy to agricultural science. I will provide perspectives from two vantage points, one from a personal view, and the other as Acting Administrator of the USDA Agricultural Research Service (ARS), the same agency my father worked for more than 40 years before he retired about 30 years ago.
He is often credited as the originator of the Sterile Insect Technique which is the principal technology used to eradicate the screwworm from the U.S., Mexico, and now all of Central America.
If he were here today, I know he would display considerable modesty at such expressions of credit directed solely at himself. I recall very clearly that he always acknowledged the important roles and contributions of a large number of other people and organizations in this remarkable achievement, many of whom are at this celebration.

Life and Family



Edward Fred Knipling, was born near Port Lavaca, Texas in 1909. He was the ninth of ten children who grew up on a farm of 150 acres. The family grew cotton and corn, raised cows, hogs, and chickens and produced almost all of their own food.
As a young man working the fields and tending the family livestock, he witnessed the devastating effects of screwworms on living animals and of boll weevils on cotton, as well as that of many other insect pests. His reputation as a keen and thorough observer of nature no doubt started as a boy on the farm.
In college he became interested in entomology while studying agriculture at Texas A and M University. He was struck by the realization of the enormous impact insects had, both good and bad, on the welfare of humanity, not only from the standpoint of food production but also with respect to human health.
Harkening back to his observations on the farm, he also formulated the vision early on of the need to manage insects to prevent damage rather than control the pests or treat their hosts after the damage had already occurred.
My Dad continued his college education at Iowa State University where he met my mother, also a doctoral student in the life sciences. They were married in 1934 and eventually had five children of which I am the third or “middle” one.

USDA Career


Other than working on his family’s farm, my father spent his entire working life having just one employer—the U.S. Department of Agriculture. He began this career in 1930, after graduating from Texas A & M, when he took a temporary job as a field hand in Mexico studying the pink boll worm on cotton.
While at Iowa State University, my father met Dr. E.W. Lockey from the USDA. Lockey offered him a job on screwworm trapping and population monitoring at Menard, Texas, beginning in 1931. He worked at Menard on an intermittent basis over a period of nine years that was punctuated with continued graduate studies and duty assignments on screwworm in Georgia and other livestock insect pests in Illinois and Iowa.
In 1935, at Menard, my father first met and began work with his long-time friend and colleague, Dr. Raymond C. Bushland. At the time, their research concentrated on treating cattle for screwworm maggots, or “wormies” as ranchers called them, after they had already invaded open wounds. Such treatments were called “smears”. My Dad realized that you could never really control screwworms that way; what was needed was some measure to prevent adult flies from infecting the animals in the first place. It would take a number of years, however, before this idea would take form and be realized. More on this later.
In addition to studying the screwworm, during the early years of his career he also directed research on mosquito biology and control in Pacific Northwest during the period 1940-1942.
When World War II began, he was transferred from Portland, Oregon, to Orlando, Florida. There he led a USDA research team assembled to work with the U.S. Army to develop repellents and controls for biting insects (e.g., flies, mosquitoes, lice) that vectored diseases such as typhus and malaria, which posed a threat to U.S. and Allied forces. This work led to the development of the insecticide DDT, which we all know has a legacy of its own. Although DDT is credited with saving millions of lives and doing much good for agriculture throughout the world, its adverse environmental effects which came to light in later years stimulated my father to continually envision more selective and environmental-friendly insect control strategies.
After the war, my father moved to Washington D.C. to become the Director of Research on Insects Affecting Livestock and Man. In 1953, he became the Director of Entomology Research for ARS. He served in that position until 1971. Following his retirement in 1973 he remained professionally active for the next 27 years as a scientific collaborator, up to the time of his death about two and one half years ago just a few days shy of his 91st birthday.


Sterile Insect Technique



The time of the development of the sterile insect technique is hard to pinpoint because it evolved over a period of about 20 years during the 1930s--1950s. Several key observations and research developments by my father and others during this time were essential to its formulation. At first it was only a vision based upon my Dad’s feeling, as noted before, of the need to prevent screwworm flies from laying eggs in the first place rather than treating the animal wounds and the flesh-eating larvae. The actual development of such a preventative method of control was triggered by several observations he made in the 1930s of screwworm behavior, mating habits, and population trends. He knew that male flies were very aggressive and mated with multiple females, but a female fly mated only once before laying her eggs. Also he noted that the natural population of adult flies, although spread over very large geographic areas, was actually quite low on a unit area basis. Furthermore, during winter months, the natural population was confined to southern most parts of the U.S. and its density even lower, perhaps only on the order of 25-50 flies per square mile.
Simultaneous with but independent of these observations, Dr. Bushland and other co-workers developed a method for rearing screwworms in the laboratory on an artificial medium for the purpose of having a large number of screwworms available for various laboratory research studies. The availability of this mass production technology, coupled with the knowledge of fly mating behavior, gave rise to the idea of raising genetically defective flies that could be released into the field to mate with and transmit the detrimental character into the wild normal flies when their population was low. Thus, it was theorized this would diminish their survival and reproductive potential and reduce the size of the next fly generation.
But my Dad had no idea on how to induce such a genetic defect. However, he continued to develop his ideas of population control using simple mathematical models based upon laws of probability. For example, he theorized that if you could release 10 Xs as many genetically defective flies as the normal ones that occurred in the wild, and if their mating behaviors were equal, the probability of a defective male fly mating with a normal wild female would be 90 percent. In other words, only 10 percent of the matings would likely occur between normal wild male and female flies. A second release of a large number of defective flies would further weaken and lower the population of normal flies. And so on to extinction.
For the most part this concept lay dormant for nearly 10 years through the 1940s when my Dad’s research and that of many of his colleagues was directed to mosquitoes and other biting insects during the war effort. However, in 1950, after my father had moved to Washington, D.C. a key breakthrough occurred. One of his colleagues, Dr. Art Lindquist, read in the scientific literature about the work of the geneticist and Nobel Laureate, Dr. H.J. Muller of Indiana University. Dr. Muller had discovered that it was possible to sterilize Drosophila, or fruit flies, by exposure to x-rays without affecting their normal sexual behavior and competitiveness.

Influential Colleagues and Collaborators



So my father wrote to Dr. Muller (lower right) and outlined his theory. Following Muller’s enthusiastic response to the idea of sterilizing large numbers of laboratory-reared screwworms, Dr. Bushland (upper right), who was then back in Texas at Kerrville, put the idea to the test. D. F. Hopkins was a key co-worker in this research. Using x-ray equipment at a nearby Army hospital in San Antonio, they exposed screwworms of different life stages to radiation, and discovered that they could be sterilized at certain doses without affecting their mating behavior or causing other serious damage. The next step was cage studies using both sterile and normal flies in various ratios. These studies confirmed the theory that reproduction of the screwworm could be inhibited at levels consistent with the mathematical probability models.
Following these exciting and promising results, larger scale screwworm fly mass rearing and irradiation capabilities were established and field testing of the sterile insect technique was initiated in 1951 on Sanibel Island, just off the west coast of Florida. This initial test was only partially successful due to the proximity of the island to the mainland which allowed reinfestation. However, in 1953 the test was repeated at a more isolated location on the Dutch West Indies Island of Curacao, off the coast of Venezuela. Within just a matter of months and about three fly generations, the test proved highly successful, resulting in the complete elimination of the native screwworm population over the entire island.
Mr. Al Baumhover was the leader of the field tests on both Sanibel Island and Curacao. You can imagine the excitement that he, my Dad, and all their co-workers felt at this success and proof of concept. Years later my Dad often reflected back and said the success at Curacao was one of the most gratifying moments of his entire professional career. Not only had the concept been proven, but he and others had overcome much adversity that was present all along the way, including skeptics, critics, opponents, and difficulty in securing financial and policy support for their research and pilot tests. However, there were others who provided encouragement and support; he was very much indebted to these people.
My Dad’s persistent optimism and tenacity to overcome obstacles were among his greatest virtues. Curacao, however, was only the beginning. Word of the astounding success of the sterile insect technique in eliminating screwworms there created a ground swell of support among livestock producers in Florida who demanded an eradication program be initiated on the mainland. To make a long story short, soon afterwards, the technique was used to systematically eliminate the screwworm from all of the Southeastern United States by 1959.



Eradication of the New World Screwworm



Most of you know the rest of the story which is why we are here today. As this display map indicates, by 1966 the screwworm had also been eradicated from the southwest and all of the United States. The Southwest Animal Research Foundation (SWARF), a livestock producer organization, was a key supporter and player in this aspect of the program and is still active today.
On August 28, thirty years ago to this very day in 1972, the U.S. and Mexico signed an agreement to eradicate the screwworm from Mexico, which was achieved in 1991. The program, as you all know, subsequently progressed successfully through all of Central America and is nearing completion this year in Panama. Truly this is a remarkable achievement that has been made possible by the combined efforts and cooperation of literally thousands of individuals and organizations. Special recognition is extended to all those here today that played a role, particularly the Plant workers, other employees of the Mexican American Commission, members of Mexican livestock producer organizations, and contributing USDA personnel.
The benefits to livestock producers throughout the eradication zone are well over one billion dollars per year. The cumulative benefits over more than 50 years, including all the economic multipliers, environmental quality, and avoidance of animal and human suffering, are too large and staggering to even estimate. If my father were here today I know he would salute you all, as I do now on his behalf and for his memory.
At this point, I’d like to recognize Ms. Lynn Stewart, from our USDA National Agricultural Library in Beltsville, Maryland. Lynn is here today with a large scale version of this map on display. Lynn is also responsible for securing and maintaining an extensive collection of documents and other materials encompassing the entire history of the screwworm eradication program from the 1930s through the present, including my father’s personal papers. The collection is currently 165 linear feet long, “on the bookshelf” so to speak, and continues to grow. The screwworm collection illustrates the important contributions of individuals, private organizations, universities, state agencies, national governments, and the Commission. The collection includes correspondence, diplomatic agreements, scientific papers and manuscripts, raw research data and analyses, livestock producer materials, films, photographs, maps, public information materials, and artifacts. In addition to the collection and this display, the Library has made the story of the screwworm eradication program available to researchers and the public on the World Wide Web as well as on compact disc. Lynn Stewart is available and anxious to meet with and talk to any of you all this week about the collection and to solicit any additional relevant material that you might be able to contribute.




As a result of his long and fruitful career as an entomologist, my father received many awards and honors including from three U.S. Presidents, other heads of state, several universities, numerous farm organizations, professional societies, international organizations, and his peers. I’ve listed some of the prominent ones here. One not listed however, of which he was most proud, was being named the first inductee into the Calhoun County (Texas) Cattlemen’s Association Hall of Fame in 1994 in his home town of Port Lavaca, Texas.

Post Retirement: Beyond Screwworm


As already mentioned, my father continued to work and contribute to agricultural science well after his “formal” retirement. He wrote numerous scientific articles and also authored two books. The one on the left, “The Basic Principles of Insect Population Suppression and Management,” was published in 1979. This book provides a comprehensive story of the sterile insect technique and much more. In 1992, he published the book shown on the right, which he regarded as his favorite and most important work. It is entitled, “Principles of Insect Parasitism Analyzed from New Perspectives.”
In these books and other publications my father discusses the limitations of today’s conventional insect control strategies based on small area, farm to farm applications; continued heavy reliance on insecticides; and reactive treatments after pest populations reach high levels and damage occurs. His alternative theme is the proactive area-wide concept in which insect populations are suppressed and kept low to prevent them reaching damaging levels. The sterile insect technique is depicted as just one of many potential tools that could be developed and applied against a whole host of pest insect populations in addition to the screwworm, resulting in great economic, agricultural productivity, and environmental benefits.

Area-Wide Pest Management

 In particular my father promoted, in his books and other writings, the use of nature’s own tools, such as host-specific parasites or other natural biological agents, to suppress pest insect populations. Much like the sterile insect technique, host-specific parasites would be reared in large numbers and released into the environment over a large geographic area to augment parasites already present and more importantly to overwhelm the wild pest insect population and reduce it to low numbers.
Furthermore, use of parasitoid technology, coupled with the sterile insect technique, would be highly synergistic and have a powerful effect on reducing or even eliminating the pest insect populations within several generations more effectively than either technology would achieve alone. Additional efficiencies could be achieved by integrating other technologies to suppress the total insect population, such as attractants, baits, resistant crops, and the like.
Again, the key to success of these approaches would be to apply them on an area-wide basis, as was done with the screwworm program. Broad-scale cooperation and coordination among governments, agencies, producers, and other organizations also are essential to the success of such programs, as we all know.
If my father had any regrets in his retired professional life, they were related to his frustration and disappointment that these area-wide principles and approaches were not being adopted and supported by the scientific community or agricultural leaders and policy makers to the extent he felt they should be.
However, he was also comforted by a feeling of optimism that some day they would be embraced and supported as the world faces ever increasing human population, food security, economic, and environmental pressures.

Relevant USDA Research


Consistent with some of my father’s visions, my colleagues in the USDA Agricultural Research Service and other research organizations are continuing to find improved and more environmental friendly ways to control insect and other pests.
In addition to further refining the sterile insect technique and developing the parasitoid technology, research is underway on pheromones and other attractants, innovative baits and trapping systems, host genetic resistance through biotechnology as well as conventional breeding methods, classical biological controls, insect mass rearing technology, aerial application technology, and even improved and safer pesticides.
Many of these technologies are being applied in various combinations for area-wide pest management programs or pilot tests now underway. All of these activities involve close partnering with the USDA Animal and Plant Health Inspection Service (APHIS), other Federal agencies, state and local governments, producer groups, universities, and/or other organizations.
One of the most prominent area-wide programs underway is the boll weevil eradication program in the U.S., hopefully to be successfully concluded in the current decade.
Other examples are area-wide pilot tests directed toward the codling moth in the pacific Northwest, the corn rootworm in the Mid-west, the leafy spurge weed control program in the Northern plains, and fruit flies in Hawaii. Additional area-wide pilot tests directed toward other pest species are being planned and implemented.

E.F.K's Vision and Legacy


In summary, I have itemized on this slide a few generic principles, already discussed, associated with my father’s values, visions, and legacy. These are:
  • Prevention rather than treatment
  • Total insect population suppression
  • Area-wide concept
  • Mathematical probability models
  • Sterile insect technique
  • Parasitoid augmentation technology
  • Pilot tests to validate and demonstrate
  • Persistent optimism and tenacity

Leading America towards a better future through agricultural research and information


 When my father presented me a copy of one of his books outlining insect management strategies, he wrote, “With my compliments and hope that you can help advance some of the concepts and principles in this publication.” I will consider myself successful when I can look back over my own career and feel that I have done this to the best of my abilities.
In this regard I hope that this presentation, as well as the occasion of this 30th anniversary celebration of the launching of the successful screwworm eradication program here in Mexico, will help promote a renewed awareness of the opportunities afforded by the sterile insect technique and other area-wide approaches to manage troublesome insect populations throughout the world.

It has been a true honor and privilege for me to be here today on behalf of both the USDA Agricultural Research Service and the Knipling family. Thank you for your attention.

Last Modified: 1/10/2005