samples. These exposures were not dam- 
aging to germination if wheat moisture con- 
tent was below 14 percent. Complete mortality 
for rice weevil adults (Sitophilus oryzae (L.)) 
was obtained with resulting grain temperatures 
of less than 38°, which indicated that selective 
heating of the insects was probably responsible, 
Higher field intensities were more effective 
for rice weevil adults, but influence of fre- 
quency and field intensity on general effective- 
ness of treatment was not clearly determined. 
Experimentally derived values for a differential 
heating factor agreed with theoretical predic- 
tion of differential heating between insects and 
grain due to exposure intheRF field. Costs for 
practical-scale treatment were estimated at 3.5 
cents per bushel, which considerably exceeded 
costs for chemical fumigants. 
Studies of wood disinfestation using RF elec- 
tric fields at 37.5 and 76 mc. (137) and 2,425 
mc. (141) demonstrated insect-control possi- 
bilities in structures where conventional heat- 
ing and chemical methods may beimpractical. 
The microwave frequencies appear to offer 
means of deeper penetration where only one side 
of the structural member is accessible. 
Use of RF energy has also been studied in 
attempts to control weed seeds by heating them 
to a lethal point (78, 91). For economic reasons, 
however, RF heating would be practical only 
if a rapid heating process was essential or if 
weed seeds mixed with crop seeds could be 
selectively devitalized. Many factors influence 
the exposure required for achievement of 
lethal heating by RF energy in seeds (104), 
and favorable conditions for selective heating 
of weed seedis are probably not very likely. 
A highly successful application of RF di- 
electric heating for pest control was rep- 
resented by a120-kw. installation for sanitizing 
feed bags (157). Bales of bags on a conveyor 
were rapidly heated without damaging the bags 
to between 104° and 116°C. to kill any disease 
organisms or insects that might be present. 
Substantial savings were effected by safely 
reusing feed bags several times. 
Other practical applications of RF energy 
for pest control have not yet developed, but 
use of this type of electromagnetic energy 
certainly merits further study. Discovery of 
destructive nonthermal effects or other im- 
provements in efficiency of the method could 
make this type of energy available for prac- 
179 
tical use. Only a narrow part of the RF 
spectrum has received any appreciable atten- 
tion in pest-control studies. Most work has 
been done in the l- to 100-mc. frequency range. 
There is a need to explore the remainder 7f 
the RF spectrum, particularly the higher 
frequencies. 
Infrared 
Possibilities for pest control using infrared 
energy have not been studied as extensively 
as parts of the RF spectrum, but infrared 
energy has been applied commercially for 
insect control in grain (138, 153). Grain was 
simply heated by radiant energy from infrared 
lamps as it moved on a conveyor belt and was 
held at temperatures lethal for insects for 
the required time. Radiant energy from a 
gas-fired infrared heater has also been used 
in research on insect control in rough rice 
(123). The lesser grain borer (RhyZzopertha 
dominica (F.) was found more resistant than 
the rice weevil, with grain temperatures of 
68° and 56°C., respectively, reported nec- 
essary for control. 
Mosquitoes are attracted to insect traps 
using regular tungsten-filament incandescent 
lamps. While such lamps are used mainly for 
lighting, they emit most of their radiant 
energy in the near infrared region. A 500- 
watt quartz infrared lamp, which emits more 
infrared and a smaller percentage of visible 
radiation, was found more effective for attract- 
ing mosquitoes than a 200-watt incandescent 
lamp in tests comparing traps equipped with 
the two different lamps (30). Longer wave- 
length infrared radiation from a lamp dipped 
in black paint, however, was found no more 
effective for attracting mosquitoes than a 
nonenergized lamp of the same type (14). 
Warmth, however, is a recognized factor in 
attracting mosquitoes (24), and beliefs have 
been expressed that certain insects may locate 
warm-blooded animals by sensing infrared 
radiation. Interesting theories based onelec- 
tromagnetic radiation and reception in the 
infrared region have been advanced by ento- 
mologists and physical scientists to explain 
the long-range location of the female by male 
moths of night-flying Lepidoptera species 
(31, 46, 90). Evidence offered in support of 
these theories is largely circumstantial or 
