control recommendations in this publication. If you are going to 
use pesticides, remember: Because some States have restrictions 
on the use of certain pesticides, check your State and local regula- 
tions. Also, because registrations of pesticides are under constant 
review by the U. S. Department of Agriculture, consult your 
county agricultural agent or State Extension specialist. For fur- 
ther information on chemical control, in addition to U. S. Depart- 
ment of Agriculture Handbook No. 331, many publications are 
available. The following are of particular interest: Billings (65), 
Brown (109), Brown (110), Gorham (301), Hickey (350), Hoff- 
man, et al. (363), Hoffman and Merkel (362), Hoffman and 
Linduska (361), National Academy of Science (555, 556), Whit- 
ten (761), and Rudd and Genelly (625). 
OTHER APPROACHES TO CONTROL 
Many conventional methods of suppressing forest insect popu- 
lations are very effective, but they are all found wanting in many 
important respects. Insecticides are often entirely effective, but 
they usually cannot be applied to large areas without endangering 
other forms of animal life. Furthermore, they usually do not hold 
pest populations to subeconomic levels for long, nor do they reduce 
the vulnerability of stands to future outbreaks. Most forms of 
biological control cannot be depended upon to suppress an out- 
break before unacceptable damage has been incurred. They are 
also incapable of preventing outbreaks, although they may reduce 
their frequency of occurrence and their magnitude, intensity, and 
duration. Because of these deficiencies, as well as those of other 
current methods of control, intensive research is underway to 
develop new or improved methods which may be used as comple- 
ments, supplements, or substitutes for them. 
Sexual sterilization is receiving much current attention be- 
cause of its potential use as a new method of control. The effec- 
tiveness of releasing males sterilized by gamma radiation was- 
established in the mid-1950’s when they were used to eradicate the 
screw-worm from the West Indian island of Curacao and from the 
southeastern portions of its range in the United States. Knipling 
discussed the principal of sexual sterilization in several papers 
(425, 428, 426, 429, 427). Several authors reported the research 
that led to the method and its use against the screw-worm (456, 
457, 129, 180, 131). Some progress has also been reported in the 
sterilization cf a few important forest insects by gamma radia- 
tion (300, 401). Further research must be conducted before the 
possibilities of using the sterile male release technique for forest 
insect control can be determined. 
Chemically produced sterility also offers promise in control. 
The appropriate chemicals are called chemosterilants because of 
their capacity to deprive insects of the ability to reproduce (89). 
Most of the chemosterilants that offer promise for practical con- 
trol are mutagenic and can be used only in ways that will avoid 
all contact between them and non-target animals (557). Chemo- 
sterilants may be administered with the insect’s food or by apply- 
ing them to surfaces to which the insects are attracted. Those 
mixed with food appear to produce maximum effectiveness and 
minimum hazard. So far, none are available for use in forest 
insect control. 
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