has become an enthusiastic customer of moth- 
proofed woolens, lawn and garden sprays, and 
the ubiquitous (90 million units per year) "bug 
bomb," 
With the increasing appreciation for and 
sophistication of the use of pesticides has 
come professional (35) and public (4) aware- 
ness of the problems inherent in their indis- 
criminate and overenthusiastic application. 
These problems may be grouped into three 
broad categories: 
(1) The lack of appropriate pesticide selec- 
tivity between pest and man and his domestic 
animals, between pest and wildlife, and between 
destructive and beneficial insects. 
(2) The selection by continued use of a pesti- 
cide of resistant races or strains, so that the 
pesticide ultimately loses much of its useful- 
ness, 
(3) The lack of environmental degradability 
for certain persistent pesticides, so that these 
accumulate in soil and within plant and animal 
tissues, where they are subject to ecological 
magnification by food-chain organisms. 
This symposium surveys current knowledge 
of the status of pest-control practices, with 
the goal of providing insight into nonchemical 
means to control pests of all descriptions. At 
the same time, it is unrealistic to imagine that 
it will be possible in the foreseeable future 
to feed and clothe the world's expanding popu- 
lation and to preserve present standards of 
health and hygiene without recourse to the use 
of chemical pesticides. Therefore, there are 
three important avenues of approach to the 
safe and proper. utilization of these 
chemicals: (1) Employment of pesticides only 
when required as emergency control measures 
for pest populations that are producing injury 
beyond the economic threshold; (2) establish- 
ment of conditions for pesticide usage based on 
minimal dosages and the most suitable formu- 
lations, timing, methods, and sites of applica- 
tion; and (3) development of new pesticides and 
methods of application that are far more selec- 
tive and far more free from problems of en- 
vironmental contamination than those presently 
in widescale use. 
SELECTIVE TOXICITY OF 
INSECTICIDES 
The definition of the word insecticide "an 
agent for destroying insects" clearly implies 
10 
selectivity of action, since the human user 
certainly does not intend to share equally with 
his intended arthropod victim in the hazards 
of unrestricted chemical warfare. Equally, he 
does not expect that his normal use of plant 
sprays will harm foliage or fruits or that ap- 
plications to livestock will be deleterious to 
animal health. Nevertheless, many substances 
used to kill insects are inherently hazardous 
to higher animals, and their selectivity is ap- 
parent only through careful application and 
confinement to the treated area. Examples in- 
clude hydrogen cyanide as a fumigant, para- 
thion as a dust or spray, and arsenic trioxide 
as a poisoned bait. 
Progress has been made in improving the 
selective action of these generally toxic in- 
secticides by localizing them precisely to the 
area needing treatment and by combining them 
in baits or with specific attractants so as to 
bring the pest to the poison. Examples include 
the use of lindane or dieldrin in seed treat- 
ment at 0.25 ounce per acre to replace a 
broadcast application of 2 pounds per acre; the 
incorporation of the specific attractant methyl 
eugenol with parathion in bait boxes to annihi- 
late male oriental fruit flies (Dacus dorsalis) 
and the incorporation of dichlorvos (dimethyl 
2,2-dichlorovinyl phosphate) or naled (dime- 
thyl 1,2-dibromo-2, 2-dichloroethyl phosphate) 
at 1 percent in granulated sugar as a bait for 
house flies to replace general residual sprays. 
The development of systemic insecticides, 
which when applied to seeds or as granular 
preparations about plant roots enter into the 
plant translocation stream and are concen- 
trated into leaves and fruits, has provided an 
important avenue for controlling plant-feeding 
pests without damage to their natural parasite 
and predator enemies and had led to the de- 
velopment of ecological selectivity. Much ad- 
ditional research remains to be accomplished 
in this general area of improving the selec- 
tivity of intrinsically nonselective materials 
by selective application and utilization. 
It is, however, in the discovery of insecti- 
cides that are truly selective in a physiological 
and biochemical way that the chemist and 
toxicologist have the greatest opportunity to 
produce the genuinely sophisticated and de- 
sirable insecticides of the future. We shall 
consider some of our present knowledge of 
selectivity as it relates to the development of 

