even if only one key insect pest out of 10, 20, 
or 30 succumbs to the magic of overflooding 
with sterile males, the prize is worth all 
research effort. Think back to the screw-worm 
profits. Nearly $400 million in savings! Less 
than $20 million expended in application of 
the sterilization principle? 
I have not yet discussed the use of sterile 
insects to control insect pests without com- 
plete eradiation as the goal. With many pest 
insects, we would only have to delay develop- 
ment for one or two generations to permit the 
crop to be harvested without serious damage. 
The release of sterile insects may be the 
ideal way to accomplish this purpose. When 
crops appear in the spring, the numbers of 
insects present are often few. Restricting 
development of these with comparatively small 
numbers of sterile insects may give control, 
especially when the insects do not fly long 
distances. This use of sterile insects deserves 
much research attention. 
I have also failed to discuss the use of 
chemosterilants to sterilize populations of 
insects in nature. We are making much prog- 
ress in our research on chemosterilants and 
have discovered numerous effective materials. 
Our hope is that we will soon find safe chemo- 
sterilants or ways of using them without 
hazard. The bonus effects possible from steri- 
lizing field populations directly without having 
to release insects sterilized in the rearing 
plant are a challenge for future research. 
CONCLUSIONS 
Progress made in research on sterilization 
procedures for insect population suppression 
permits the following conclusions: 
(1) Releases of sterile males in numbers 
sufficient to grossly overflood wild insect 
populations provide an ideal nonchemical means 
of combating key insect pests when the latter 
satisfy basic requirements of the method. 
(2) Eradication or control of a number of 
important insect pests should be feasible 
through application of the sterilization prin- 
ciple, no matter whether the insects are 
present in isolated infestations or have wide- 
spread continental distribution. 
(3) The sterile male release method will 
not be feasible for use on many insect pests 
because of incompatible mode of existence, 
behavior, method of reproduction, or the 
obstacle of excessive numbers unless the 
excessive numbers can be overcome with 
practical population thinning procedures. 
(4) Most effective use of the sterile male 
release method will be to snuff out or main- 
tain continuous control of low-density popu- 
lations achieved through application of other 
control procedures or resulting from natural 
causes, 
(5) Released sterile insects may serve an 
important role in regulatory, eradication, and 
control programs as barriers tothe establish- 
ment of introduced foreign pests or the spread 
of established infestations. 
(6) Although the cost of sterilization re- 
search and application of sterile insects may 
be high in contrast to that involved in de- 
veloping broad-spectrum insecticides, there 
is no end to the benefits that will result when 
eradication has been achieved. 
(7) The still largely untapped potential of 
sterilization methods for eradicating or con- 
trolling insect pests should be exploited fully 
in the years to come and receive all possible 
support. 
VETEBRATE PEST CONTROL BY BIOLOGICAL MEANS 
David K. Wetherbee, Massachusetts Cooperative Wildlife Research Unit, 
Fish and Wildlife Service, U.S. Department of the Interior, 
and College of Agriculture, University of Massachusetts, Amherst 
"Biological control" is really an indefinable 
label applied to fighting biology with biology, 
especially in limiting the growth of or in ac- 
tually reducing the size of populations. All 
animals and populations of animals are limited 
102 
and abetted in their success by that indivisible 
trinity of physics, chemistry, and biology that 
makes up their ecological niches and body 
physiologies. Biology never acts alone. 
a 
