sterilized cannot reproduce. From the standpoint of reproduction, this 
result is equivalent to killing the 900 insects. In addition, however, the 900 
sterile insects can now compete with the 100 normal fertile insects that 
remain in the population and theoretically prevent reproduction in 90 of the 
normal insects. Thus, only 10 of the normal insects would be expected to 
mate with fertile insects and be capable of reproducing. In addition, if some 
of the sterile insects survive to overlap the subsequent generation, further 
adverse effects on the reproductive potential of the population can be 
expected. No such "'time'' effect can result from the killing system. 
An important problem in connection with this type of insect sterility 
control is the development of safe and effective means for initially steriliz- 
ing a part of the natural insect population. The use of chemosterilants in 
conjunction with attractants that will lure insects in large numbers may be 
the answer. Research in that direction is in progress. 
USDA entomologists and chemists have screened 3,000 materials and 
have found that at least 50 of them produce sterility in insects. Of the mate- 
rials that have the ability to sterilize insects, three are most promising. 
They are apholate, tepa, and metepa. The materials that have shown most 
promise against both sexes of insects belong tothe same class of chemicals 
that possess activity against certain types of cancer. Our chemists and 
entomologists are therefore cooperating closely with scientists of the 
National Institutes of Health in the evaluation of materials that are of 
interest in research on cancer. 
Little is known about the hazards that may be associated with the use 
of chemicals that sterilize insects. Since these chemicals produce sterility 
comparable to that produced by gamma rays or X-rays, researchers working 
with them are proceeding with extreme caution. Investigators must take 
extra care in handling the materials in the laboratory just as they do in 
handling radioisotopes. Field tests must also be carried out with great 
caution. It is anticipated that safe use of a chemosterilant of the type now 
known to be active may be possible only when the chemical is employed in 
such a way that the target species of insect only will be exposed to it. Con- 
sequently, research on chemosterilants has given greater impetus to 
investigations on specific insect attractants. 
Even though practical ways of using chemosterilants have not yet been 
developed, much progress has been made in testing chemicals that will 
produce sterility when the materials are ingestedor contacted by the insect. 
The insects that have been sterilized under laboratory conditions by the use 
of chemosterilants include the stable fly, house fly, horn fly, face fly, 
screwworm, green peach aphid, boll weevil, pink bollworm, plum curculio, 
Mexican bean beetle, codling moth, citrus red mite, two-spotted spider mite, 
yellow fever mosquito, common malaria mosquito, oriental fruit fly, melon 
fly, Mediterranean fruit fly, Mexican fruit fly, cabbage looper, fall army- 
worm, locust borer, German cockroach, and Drosophila fruit flies. 
Limited field tests in semi-isolated areas have shown that house fly 
populations can be greatly reduced by using fly baits containing a chemo- 
sterilant. 
Sex Lures and Other Attractants 
Chemicals emitted from the body of the female of certain species of 
insects help the male in locating amate.Some structurally related synthetic 
HZ 
