growing concern over problems associated 
with insecticide usage, mostly those caused 
by objectionable residues. The sterility method 
is one of the most promising of new approaches 
that someday may permit us to reduce signifi- 
cantly the quantities of insecticide now re- 
quired to control insects. An adequate, healthy 
food supply for our people requires good 
insect control. 
PRACTICAL USES FOR STERILE 
INSECTS 
Thus far, the effectiveness of the sterile 
male release method has been demonstrated 
against five species of insects. All are strong- 
flying Diptera, The most notable success was 
achieved with releases of sterile screw-worm 
flies. This insect infests wounds of cattle and 
other animals, often causing their death. How- 
ever, equally significant in demonstrating the 
feasibility of the concept were successful 
western Pacific island tests involving the 
oriental fruit fly and melon fly. These are 
important tropical fruit fly species that infest 
a variety of fruits and vegetables and can 
cause great economic losses. Releases of the 
Mediterranean fruit fly, another major pest 
of tropical fruits, reduced natural infestations 
in partially isolated pilot tests in Hawaii and 
Costa Rica. 
A unique, practical use of sterile flies was 
the substitution, in 1964, of releases of sterile 
Mexican fruit flies for costly and objectionable 
spray programs to protect against the annual 
invasion of this fly into the Tijuana and adja- 
cent southern California areas. 
Research on methods of sterilizing insects 
by radiation is in progress, with field tests 
under way or planned, for the following insects; 
Gypsy moth (Porthetria dispar (Linnaeus)), 
codling moth (Carpocapsa pomonella (Lin- 
naeus)), pink bollworm (Pectinophora gossy- 
piella (Saunders)), tsetse fly (Glossina morsi- 
tans Westwood), boll weevil (Anthonomus 
grandis Boheman), cockchafer (Melolontha 
vulgaris F.), and vinegar fly (Drosophila 
melanogaster (Meigen)). Our prospects appear 
reasonably good for the practical application 
of the technique against these species, espe- 
cially when the method is integrated with other 
methods of control. 
97 
Insects that have been or are now the subjects 
of considerable sterilization research include 
the following: Corn earworm (Heliothis zea 
(Boddie)), tobacco budworm (Heliothis vires- 
cens (Fabricius)), tobacco hornworm (Proto- 
parce sexta (Johannson)), sugarcane borer 
(Diatraea saccharalis (Fabricius)), European 
corn borer (Ostrinia nubilalis (Hubner)), Orien- 
tal fruit moth (Grapholitha molesta (Busck)), 
olive fruit fly (Dacus oleae (Gmelin)), Medi- 
terranean flour moth (Anagasta Kuehniella 
(Zeller)), certain mosquitoes that may create 
disease or comfort threats in isolated areas, 
and Queensland fruit fly (Dacus tryoni (Frog- 
gatt)). 
It is unlikely that the sterile insect release 
technique will be feasible or practical for all, 
or even most, of these species. However, suc- 
cessful application of the method against even 
a few of the major species could contribute 
materially to the overall objective of developing 
ways to control insects with no adverse side 
effects. As yet, researchers are not investi- 
gating the potential value of the method against 
many other insect species, present in different 
parts of the world, that would be favorable 
candidates for its application. A breakdown in 
behavior caused by radiation dosages required 
for sterilization appears to be one of the most 
common limiting factors. We hope that means 
of avoiding radiation damage, such as sub- 
stitution of chemosterilants for radiation, 
fractionation of radiation dosage, or even 
selective application of radiation to only apart 
of the insect body, may ultimately provide 
solutions to the behavior breakdown problem. 
Research on the screw-worm fly, conducted 
under R. C, Bushland at the U.S, Department 
of Agriculture laboratory at Kerrville, Tex., 
established that a dosage of 5,000 roentgens 
of ionizing radiation from an X- or gamma 
ray source, applied to 7-day-old screw-worm 
pupae, would impart sterility to both sexes of 
emerging adults. Dosages up to 20,000 
roentgens did not appear to seriously affect 
the vigor of the flies. When normal females 
were mated with sterile males, the normal 
females laid only infertile eggs throughout 
their lifespan. Thus, whenever a sterile male 
mated with a normal female, the effect was 
equivalent to destruction of the female. 
After the soundness of the concept of over- 
flooding normal screw-worm flies with sterile 

