Sterile-Male Method—Past and Future 
Aside from its accomplishments in the Southeastern 
U. S., the sterile-male method of pest eradication has had 
successes elsewhere. It has been proposed for many 
problems and is being used for some of them. 
The first great success was elimination of the screw- 
worm fly on the island of Curagao in 1954. A pilot test 
reduced screwworm incidence by 70% in a 2,000-square- 
mile area of Florida in 1957 before the full-scale attack 
was launched. 
In cooperation with the government of Mexico, the 
U. S. Department of Agriculture has done some promising 
research work with this method against the Mexican 
fruit fly. 
Belgium is working on a program to apply the sterile- 
male method to eradication of the tsetse fly in its African 
colonies, and a facility in Hawaii is directed at several 
fruit flies. The females mate more than once, but the 
mathematics of the method show that if sterile males 
make enough eggs sterile, the method may work with 
such insects (2). It has also been stated that such pests 
as small rodents might surrender to this kind of as- 
sult (2). 
good for only a few days to a week at a time, and even if 
you clean up your herd completely, you can expect rein- 
festation from such animals as deer, raccoons and rabbits. 
Eradication is accomplished by causing females to mate 
with sterile males (2). Afterward the female lays her 
sterile eggs, unaware that she has been frustrated in her 
natural purpose and apparently satisfied; she does not 
breed a second time. 
The method depends for its success on rearing and steri- 
lizing adequate numbers. In the Florida operation this 
has required an average of 50 million flies a week. A 
maximum of 70 million a week was reached, and full plant 
capacity was 100 million a week. 
The fly factory is a converted World War II B-17 hangar 
at Sebring, Fla. It measures 160 X 200 ft and had oper- 
ations on two floors. The ground floor is shown in Fig. 1. 
Three million fertile flies in a darkened adult colony pro- 
duced larvae, which came to maturity on the upper floor 
and dropped through funnels into sand trays for pupation 
in the pupae-holding room. Pupation requires ~8 hr. 
After that pupae were held for 5.5 days at 80° F and 95% 
relative humidity to mature. 
During the maturing period the trays remained at body 
temperature and moved slowly along as food was added 
and waste removed. Food requirements indicate the 
magnitude of the operation: 40 tons of ground meat, 9,600 
gal of water, 4,500 gal of beef blood, 65 gal of plasma, and 
35 gal of honey were required each week. 
Sexual sterility was produced by exposing the pupae to 
8,000 r of Co® radiation two days before appearance of 
adult flies. Early research and tests showed that sterile 
males could be obtained with a dose of 5,000 r while 
10,000 r had no adverse effect on development of the pupae 
(3-5); 8,000 r sterilizes the females among the released 
flies as well as the males to assure that there is no inad- 
vertent contribution to the healthy population. 
Elaborate precautions assured that none of the fertile 
flies escaped from the fly factory. These included changes 
of clothes and showers for all employees as they left work. 
Distributing the Flies 
Once reared and sterilized the fly battalions traveled to 
their theatres of operation in small Cessna 172 airplanes. 
Each plane carried 1,000 boxes of flies and flew for 5-6 hr 
each day over prearranged patterns in Florida and parts of 
Alabama and Georgia. 
Pilots flew at 1,500 feet whilé insect dispersers loaded 
automatic ejectors. The ejectors dropped the boxes and 
opened them at a rate that dispersed 100-800 flies to each 
square mile of terrain. An air-conditioned station wagon 
carried flies to places that were hard to reach by plane. 
To relieve anxieties of the human population, each box 
was marked to indicate the harmlessness of box and con- 
tents. Screwworm flies don’t bite or look for picnic tables. 
Irradiators 
The radiation source used for early field tests was a 
cylindrical arrangement of Co® slugs designed and built by 
Oak Ridge National Laboratory (6). This source was 
quite satisfactory and served as the basis for an irradiator 
of greater capacity and somewhat more uniform field. 
Figure 2 shows one of the Co® units at Sebring. The 
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