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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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1 - Presented by Dr. E. B. Knipling
2 - Life and Family
3 - USDA Career
4 - Sterile Insect Technique
5 - Influential Colleagues and Collaborators
6 - Eradication of the New World Screwworm
7 - Awards
8 - Post Retirement: Beyond Screwworm
9 - Area-Wide Pest Management
10 - Relevant USDA Research
11 - E.F.K's Vision and Legacy
12 - Leading America towards a better future through agricultural research and information
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.
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Last Modified: 1/10/2005
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