habit in an insect species, as in the case of the screwworm, is not an 
essential requirement for the application of the sterility principle. 
Research has been conducted on several other species of tropical fruit 
flies. Tests have shown that the reproductive potential of the Mediterranean 
fruit fly, the Mexican fruit fly, and Drosophila fruit flies also can be ad- 
versely affected by the sustained release of sterile insects. The boll weevil 
has been eliminated in a smallisolated field by the release of large numbers 
of chemically sterilized males. 
In laboratory investigations the reproductive potential of caged insect 
populations has been reduced by introducing sterile insects of a wide range 
of species, including certain mosquitoes, the house fly, face fly, pink boll- 
worm, codling moth, European corn borer, and gypsy moth. Canadian 
entomologists have shown that the reproductive potential of the codling moth 
can be greatly reduced bythe use of sterile males introduced into field cages 
containing populations of normal moths. 
Much research must be conducted on each insect problem to determine 
if the release of sterile insects will be useful in practical control or eradi- 
cation efforts. Field experiments are usually difficult and costly. However, 
sufficient progress has already been made to justify a continuation and 
intensification of research both in the laboratory and in the field on such 
species as the oriental, Mediterranean, melon, and Mexican fruit flies, the 
boll weevil, pink bollworm, codling moth, tobacco hornworm, and Drosophila 
fruit flies. 
Sterilizing Insects in the Natural Population 
The sterility principle has its greatest potential when used in ways that 
will induce continuing sterility within the natural insect pest population. 
Research in this area has not advanced to a stage that the method can be 
used in practical insect control. However, because of the great potential of 
the method, intensive exploratory research is under way by USDA entomolo- 
gists and chemists. 
It has been shown that when sterile insects are released and compete 
with the normal insects for reproduction, the biotic potential of the natural 
population can be greatly reduced. A scientist of the Department then 
reasoned that if it were possible to sterilize instead of killing a given per- 
centage of the insects in the natural population, it should be possible to 
achieve a double effect on the reproductive potential of the total number of 
insects in that population. The insects sterilized could not reproduce. Thus 
the immediate effect on the population and its potential for reproduction 
would be the same as if an equal number of the insects had been killed by 
an insecticide. However, if the method of producing the sterility did not 
seriously interfere with the normal behavior and competitiveness of the 
insects that have been made sterile, the sterile insects in turn would be able 
to adversely affect the reproductive potential of the normal insects remain- 
ing in the population. 
The great advantage and potential of producing sterility in a population 
of insects or other pests instead of killing portions ot the population can be 
illustrated by the following theoretical situation: If the natural population of 
an insect within the area of competition consists of 1,000 individuals and 
900 are killed with an insecticide, 100 insects will survive to reproduce. If, 
however, in a similar area 900 of the 1,000 insects are sterilized, those 
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