of insects (3, 61, 69a), and modern electron- 
ics equipment has been employed in analyses 
of these sonic and ultrasonic signals (3, 61, 
69a, 82). Sounds of different species were 
found to have specific characteristics (3) and 
can be used for identification purposes (82). 
Possible applications of acoustic energy 
for insect-control purposes have recently been 
reviewed (15, 57). Some insect species have 
been attracted with artificial sounds and re- 
cordings of their own calling songs (15, 57, 
61). In attempts to control mosquitoes, males 
were successfully attracted and killed with 
electric grids, using recordings of the female 
flight sounds (61), but the method was not 
successful for control because few males are 
required tc maintain the reproductive capa- 
bility of the population (57). Other studies in 
attracting. mosquitoes showed. that..a- funda-.. 
mental sine-wave tone attracted males as well 
as recorded flight sounds of the female mos- 
quito when the sine-wave frequency matched 
the dominant tone of the female flight sounds 
(151). Studies by the same investigators also 
indicate that the mosquitoes use a phase 
principle in orienting to a sound source rather 
than a Doppler principle or an intensity- 
gradient-sensing method (152). 
There has been speculation that flies may 
react to sound, but studies have been very 
limited and inconclusive (22, 57). Because of 
insecticide problems with dairy cattle, studies 
of the influence of sound on flies have recently 
been initiated by the Agricultural Research 
Service, U.S. Department of Agriculture. 
Still other insect reactions to sound have 
been observed. Swarms of certain Diptera 
respond to sound (59). Swarms were startled 
by sounds with frequencies between 80 and 
800 c.p.s. and gathered around the sound 
source only at frequencies near 125 and 250 
c.p.s. Sound of sufficient intensity between 
300 and 1,000 c.p.s. transmitted through bee- 
hives caused the insects to remain almost 
motionless, so that apiculturists could per- 
form their work without using bee smokers 
(62). 
No practical control measures using sound 
to attract insects have yet been developed, 
but there is need for further research on 
acoustical behavior of insects, from which 
practical methods for control might evolve 
(57). 
184 
Another acoustic response that is being 
investigated for control possibilities stems 
from the observation of evasive flight maneu- 
vers that some moths perform when threatened 
with capture by bats, Bats emit sequences of 
ultrasonic pulses when flying and use the 
echoes to locate obstacles in their flight path. 
They also use this sonar system to locate and 
track flying insects. Studies have shown that 
bats emit these high-pitched chirps at the 
rate of about 10 per second and that the 
frequency of vibration is about 80 kc. (120). 
Extensive studies both in the laboratory and 
in the field have shown that certain moths 
detect the ultrasonic pulses of the bats and 
take evasive flight action to avoid capture by 
bats (120). The nature of tympanic nerve 
responses in moths was studied when the 
moths..were subjected. both -to.. artificially 
produced sounds and those from flying bats. 
Flight patterns of moths in the field were 
photographed as the moths were exposed to 
batlike ultrasonic pulses. Reactions included 
abrupt and bewildering changes in direction, 
tight turns, climbs, loops, and dives to the 
ground. These observations have been con- 
firmed by other scientists (15). 
Further evidence that the moth flight re- 
actions were due to acoustic stimuli was ob- 
tained by equipping insect light traps with 
ultrasonic sources and comparing insect 
catches with those of identical light traps that 
had no ultrasound equipment (15, 139). Re- 
corded and imitated bat pulses and continuous 
ultrasonic energy at different frequencies 
were studied (15). Evasive flight of moths was 
observed due to the ultrasonic stimuli, and 
catches of moths in the ultrasonic traps were 
much lower. Among several factors noted in 
results of the experiments were differences 
in the repelling frequencies for moths with 
thoracic tympanic organs and those with ab- 
dominal tympana (139). In some studies the 
ultrasound appeared less effective in repelling 
insects during damp weather (15). 
Because of the dramatic’ effects of batlike 
sounds on moth flight activity, studies are 
now underway at two locations at least to 
evaluate the principle for practical use in 
protecting crops from certain insects, Ex- 
periments in Ontario (15, 16) showed that 
broadcasts of batlike ultrasound over a plot 
of sweet corn reduced infestation by the 
