European corn borer by greater than 50 per- 
cent. While this method repels the insects 
rather than destroying them, if applied over 
a large enough area, the population might be 
reduced by modification of the mating and 
ovipositing behavior (16). 
Laboratory and field studies on the effects 
of ultrasound similar to that used by bats are 
also underway in South Carolina to evaluate 
this principle for control of the cotton boll- 
worm (Heliothis zea (Boddie)) (2). Studies of 
tympanic nerve response indicate a maximum 
response to ultrasonic stimuli inthe frequency 
range from 21 to 27 kc. for this species 
(Taft, pers. commun., 1964). Responses of the 
tobacco budworm (Heliothis virescens (F.)) 
and the cabbage looper (Trichoplusia ni 
(Hiibner)) are also being investigated as to 
effects of sound stimuli duration, frequency, 
pulse shape, and pulse repetition rate. 
Further evidence that sound energy may af- 
fect ovipositing behavior of insects has been ob- 
tained recently in studies with stored-grain 
insects. Exploratory studies in which Indian- 
meal moths were continuously exposed to a 
low-level hum from loudspeakers during a 
4-day oviposition period indicated a much 
lower emergence and poorer survival for in- 
sects from eggs deposited during exposure to 
sound (84), 
The future of sonic or ultrasonic methods 
for insect-control purposes is difficult to 
predict. Certainly more research is needed 
in this area to better understand the effect 
of acoustic factors on the behavior of various 
species. Depending on the findings, sound and 
ultrasound may very well be among pest- 
control methods of the future. A phenomenon 
worthy of mention here has been reported on 
the auditory detection of modulated radio- 
frequency energy by humans (51). By some 
detection mechanism in the head, fairly weak 
RF electromagnetic fields were perceived as 
sound characteristic of the pulse modulation. 
To our knowledge this capability has not been 
observed nor looked for in insects. If some 
similar mechanism were active in insects 
whereby acoustic signals might be detected 
from modulated RF energy, the problem of 
transmission of acoustic stimuli would be 
greatly simplified. 
Control of Birds 
Sound also has been used experimentally 
and in practice to repel both mammals and 
birds (58); however, only work on birds is 
included in this paper. 
For many years, pyrotechnic devices, car- 
bide or acetylene exploders, and rifles and 
shotguns have been the principal sound sources 
used to repel birds. Research has shown that 
birds often can be repelled or crop damage 
lessened with use of pyrotechnic devices. 
Rockets, aerial flash bombs, and rope fire- 
crackers were useful in protecting ricefields 
against red-winged blackbirds (Agelaius 
phoeniceus), grackles (Quisalus quiscula), and 
cowbirds (Molothrus ater) (100). The rope- 
firecracker technique when properly employed 
has been very effective in protecting rice 
(100) and sweet corn (101). Rockets are not 
used much today in the United States, probably 
because of high costs; however, 300- and 600- 
meter rockets are used with some success in 
Germany and Switzerland to frighten starlings 
(Sturnus vulgaris) from roosts and vineyards 
(28; Keil, pers. commun., 1962). Rockets 
generally are used with other sound sources, 
for example, gunfire, or distress calls. In 
England, rockets and aerial bombs have been 
used with shotguns to disperse starlings from 
roosts. Intensive efforts have cleared a roost 
by the fourth night (19). 
The exploding shotgun shell (hereafter called 
the shell cracker), with a range of 100 yards, 
has been excellent for frightening ducks from 
grain fields (154). During the past 6 years, 
several hundred thousand shell crackers have 
been used in the United States to repel ducks 
and blackbirds from crop fields, starlings 
from roost sites, and many different species 
from airports (47, 125). In England, similar 
devices called ''smoke puffs'' have been used 
to frighten birds from airfields, but they usually 
have been combined with bird distress calls 
(23). Short-range shell crackers (60 meters) 
are used also in Germany at cherry orchards 
and vineyards, again usually with other de- 
vices (28). In Canada, 12-gage shell crackers 
have been compared with Very pistol flares 
and marine signal rockets, and though the 
tests were limited, the flares or rockets 
