circular area 12 miles in diameter, tobacco 
hornworm moth populations were reduced by 
more than 50 percent. Further reductions were 
observed during the last two seasons. 
Because of these promising results, light 
traps have been installed in several parts of 
the United States for field trials in controlling 
tobacco, cotton, and vegetable insects. Many 
of the installations do not include plans for 
scientific evaluation. At the present time, 
there is not sufficient evidence to assure that 
field installations of insect light traps will 
provide the desired control for any species, 
but indications are interesting, and additional 
research in these methods is certainly needed. 
Possibly more important than the applied 
research on visible and ultraviolet radiation 
for insect control is the basic research needed 
to develop.further understanding of phototaxis 
and the action spectra for various economic 
insects. Basic information of this type should 
point the way to development of more suitable 
radiant attractants and more efficient traps 
for use in insect control. The basic and applied 
research in this field should certainly be 
complementary and may well achieve direct 
practical insect-control methods of real sig- 
nificance. 
Very recent studies indicate other possible 
ways in which visible and ultraviolet radia- 
tion might some day be applied for insect 
control. These hopes stem from observations 
that light exposures as brief as a photoflash 
during a critical time in the normal dark 
period can upset the life cycle of an insect 
(161). Such flashes of light prevented normal 
diapause in insects held under laboratory 
conditions, which simulated diurnal changes 
in lighting. Much more research will be 
needed, but, if insects could be forced to bypass 
their normal diapause under field conditions, 
control may be possible, since their ''timing"' 
would be off schedule with respect to seasonal 
climatic conditions. 
Daily exposures of a few minutes to red and 
far red light were also found toinhibitin other 
ways the normal development of some insects 
(12). Photoperiodic phenomena are important 
aspects in insect and animal life as well as in 
plant life (1, 116), and as these become better 
understood possible control methods may be 
developed. 
X-Rays, Gamma Rays, and Other 
Ionizing Radiations 
181 
X-rays and gamma rays comprise the high- 
energy end of the electromagnetic spectrum. 
They are extremely penetrating types of ra- 
diation. X-rays are emitted when orbital 
electrons in the inner shells of atoms near 
the nucleus change from a higher energy 
level to a lower level. Gamma rays, on the 
other hand, are emitted from the nuclei of 
radioactive materials and arise from the 
nuclear disintegration and other reactions. 
They may also result from the annihilation 
of an electron pair (negative electron and 
positron). There is an overlapping in the 
spectrum of X-rays and gamma rays (fig. 1). 
The nature of the two in this regionis believed 
to be the same except for their origin. 
Effects of X- and gamma radiation on 
biological material arise from ionization of 
the atoms in the tissues, and can be very 
damaging if sufficient energy absorption re- 
sults from radiation exposure. Similar bio- 
logical effects are produced by particle radia- 
tions, such as alpha, beta (energetic electrons), 
neutrons, and accelerated electrons, but they 
have differing penetration characteristics and 
mechanisms of absorption. 
A considerable amount of research has been 
conducted and is continuing on the use of 
ionizing radiation for pest control. A classic 
example of radiation applied to solve a severe 
insect problem is furnished by the program 
that eliminated the screw-worn (Cochliomyia 
hominivorax (Coquerel)) menace in the South- 
eastern United States. The principle involved 
the sterilization of male flies with gamma 
rays from cobalt-60 and their release inlarge 
numbers to mate with normal females, which 
mate but once, thus producing nonfertile eggs 
and eventual elimination of the population 
(29, 80, 85, 86, 87). Similar methods eradicated 
the melon fly (Dacus cucurbitae Coquillett) 
on the Pacific island of Rota. Effects of ionizing 
radiation on reproductive ability of the Euro- 
pean corn borer (Pyrausta nubilalis (Hiibner)) 
have also been considered (142), 
Application of the ''sterile-male"’ control 
method is limited by certain environmental 
and biological factors. Control by direct ir- 
radiation appears to have wider potential 
