1961] 
Insect Control Programs 
99 
the flies can complete their larval growth. The pest has caused live- 
stock losses of 20-40 millions of dollars annually, about half of this 
figure in the Southeast. 
Eradication , Operations 
The story of screw worm eradication in the Southeast begins in 1936 
with the work of Melvin and Bushland, 3 who learned how to culture 
the insect in the laboratory en masse on ground meat, blood and water 
containing a small amount of formaldehyde to retard spoilage. Dr 
E. F. Knipling, now heading entomological research in the USDA, 
speculated in conversation in 1938 that the known habits of the 
females suggested that they might mate only once, which if true meant 
that laboratory-reared sterile males might be used to control isolated 
populations such as the one in Florida. The idea was not followed 
up until after the war, when Knipling directed that the mating habits 
and physiology of screwworm flies be studied in detail, and that 
attempts be made to find chemicals capable of rendering the males 
sterile. In 1950, a general paper was published by H. J. Muller, in 
which this famed geneticist pointed out that Drosophila fruit flies in 
the laboratory were sterilized by irradiation. A colleague, A. W. 
Findquist, passed this paper on to Knipling, who then contacted 
Muller about the possibility of employing radiation sterilization on 
screwworms. The reply encouraged Knipling to initiate experiments, 
and Bushland and Hopkins eventually established that screwworms 
were readily sterilized by irradiating pupae that had been held at 8o° 
F. for five days. A dose of 2,500 r sterilized males, and 7,5°° r pre- 
vented egg production altogether. Adult males emerging from irradi- 
ated pupae proved able to mate normally with untreated females, but 
the egg masses resulting were of course infertile. Determination of 
critical doses proved to be laborious and time-consuming, but coop- 
eration with cytogeneticists soon gave rise to important short-cuts in 
the process, because damage could be assessed by cytological examina- 
tion instead of waiting for the full life cycle to carry through in 
order to get results. 
Field tests run on Sanibel Island, two miles off the Florida coast, 
proved that its screwworm population could be reduced by the release 
of 100 sterilized males per square mile per week, a figure that sur- 
passed the number of native males. But Sanibel is so close to the 
mainland that it was easily reinfested, so eradication could not be 
attempted there. 
The conclusive eradication test was finally performed on the Dutch 
island of Curacao in the south Caribbean Sea. Screwworms were 
