SCREWWORM ERADICATION—KNIPLING 4\1 
most promise was the use of sterile males for release among a natural 
population of flies. Several entomologists and geneticians had dem- 
onstrated that X-rays would cause sexual sterility in insects. 
This approach to screwworm control was proposed to a number 
of scientists, but little enthusiasm for its posssibilities was gener- 
ated. The war years, which led to emphasis on medical entomology 
problems, delayed investigations. However, following the war more 
serious thought was given to the initiation of research on the prob- 
lem. Survey records of past years and published data on screw- 
worm incidence, particularly in the Southeast, were studied for the 
purpose of estimating the number of flies present in an area dur- 
ing periods of low population density. Potential costs of rearing the 
insect in terms of millions per week were calculated. ‘Theoretical 
trends in the screwworm population were calculated on the assump- 
tion that it might be feasible to dominate the wild male population 
with sexually vigorous but sterile males. There were many unknowns 
in screwworm behavior, ecology, population dynamics, and reaction 
to irradiation, and it was recognized that failure of any one of sev- 
eral seemingly plausible assumptions could demonstrate the imprac- 
ticability of the method. However, the results of the theoretical cal- 
culations were too impressive to ignore. 
The decision to commit limited research funds to this approach 
was made following communications in 1950 with H. J. Muller of 
Indiana University, noted geneticist, Nobel prize winner, and author- 
ity on the effects of X-rays on organisms. When the general pian 
for screwworm eradication by the release of sexually sterile males was 
outlined to him, he responded with enthusiasm and encouragement 
and also offered advice on procedures to follow in determining the 
effects of X-rays on the insect. 
A definite research program on the problem was initiated in 1950. 
The work was undertaken at the Kerrville, Tex., laboratory, under 
the able direction of R. C. Bushland. Before the X-ray studies were 
begun, G. W. Eddy, then with the Kerrville laboratory, made some 
observations on the frequency of mating among females of the screw- 
worms. These observations, later confirmed by Bushland, indicated 
that the females were monogamous in mating habits. At that time 
the frequency of mating by the females was regarded as a vital point 
in the potential feasibility of effecting control by the sterile-male 
approach. Information obtained since that time, however, indicates 
that although multiple mating may reduce the effectiveness of sterile 
males, this is not necessarily a limiting factor in the successful appli- 
cation of this method. 
Bushland and Hopkins (1951) established that screwworm males 
could be made sterile by exposing pupae near maturity to 2,500 roent- 
