IOO 
Psyche 
[June-September 
reared at Orlando, Florida, and irradiated in a cobalt-60 source 
built at Oak Ridge. At first, flies were released by air at a rate of 100 
males per square mile per week, but this proved only fractionally 
effective because the swarming, unattended goats and sheep of 
Curacao harbored a much larger screwworm population than had 
been encountered in Florida. The release rate was accordingly in- 
creased from 100-400 males per square mile per week, and the first 
saturation of the island with sterilized flies caused substantially more 
than half of the egg masses laid on test animals to be sterile. After a 
month of continued releases, when another generation of adults 
emerged, the native flies were so reduced in numbers that the percent- 
age of sterile matings increased greatly. The emergence of the second 
generation of wild flies saw the proportions so altered that practically 
all matings were sterile ones. By generation III, only two egg masses 
were found in goat pens on the island, and both of these were sterile. 
No more screwworm eggs were found during the additional two 
months that flies were released on Curacao, and release was terminated 
in January, 1955, less than six months after the first flies were let go. 
The Curasao experiment, heartening as it was, also showed the need 
for improved procedures for mass production of sterilized males. At 
a rate of 400 males per square mile, the 50,000 square miles of the 
overwintering area in Florida was estimated to require 20 million 
males weekly. The females produced equal the males in numbers and 
are not easily separated from them in practice, so these doubled the 
necessary weekly rate of release to 40 million flies. An additional ten 
million flies had to be reared to make up for mortality of pupae and 
to provide for breeding stocks. This came to a weekly grand total 
of 50 million flies, in contrast to the 170,000 larvae raised each week 
for the Curacao test. 
To meet this demand, experts on insect rearing, irradiation methods 
and mass production engineering cooperated to transform a large air- 
plane hangar near Sebring, Florida, into a wonderfully efficient plant 
capable of producing more than the needed number of sterile screw- 
worm flies each week. This plant employed fully modern production 
line techniques, with the larvae being carried through their feeding 
life and thence to the pupal stage and the irradiation chamber on a 
continually moving line of stacked trays suspended from a monorail. 
Full safeguards were provided against possible escape of unsterilized 
flies, and elaborate precautions set up to protect the employees from 
radiation and from: the odor of the meat-blood larval food. 
Designed, built and equipped on a “crash” basis in just nine months, 
and at a cost of under a million dollars, the plant moved into full- 
