Pi eiaNOd'sS PAUID UiB.O NAB IeE THEN 7 
Egypt, and several places in this 
country. 
Recurrently, when such infesta- 
tions have been closely analyzed, 
it has been found that they were 
triggered by the elimination of the 
natural enemies which normally 
restrain or completely repress 
pests and potential pests. 
The significance of naturally 
occuring biological control is il- 
lustrated by its role with certain 
crops. Take alfalfa, for example. 
In California there are about 1.25 
million acres of irrigated alfalfa, 
which approximates one-sixth of 
the state’s total irrigated crop 
acreage. California alfalfa has an 
annual cash value of about $180 
million, which makes it a massive 
crop. 
Alfalfa teems with insects. It 
has been determined by research 
that about 1,000 species occur in 
California alfalfa. Yet less than 
half a dozen of these are pest 
which significantly affect the crop, 
and these cause damage only spor- 
adically. Naturally occurring bio- 
logical control is a major factor 
in keeping most potential alfalfa 
destroyers at nondamaging levels. 
We know this from experimenta- 
tion and observation, and because 
certain insecticide uses cause erup- 
tions of a considerable spectrum 
of pests. 
This is not only true for alfalfa. 
Similar data is also available from | 
other crops, including cotton, 
grape, strawberry, citrus, peach, 
pear, almond, and walnut. Collec- 
tively these comprise a major por- 
tion of California’s enormous ag- 
ricultural wealth. It is no exag- 
geration to say that these crops 
probably could not be economical- 
ly produced if it were not for nat- 
urally occurring biological con- 
trol which affects their pests and 
potential pests. 
This points up a basic anomaly 
in modern pest control, wherein 
synthetic organic insecticides, de- 
signed to be effective insect kil- 
lers, have lost much of their po- 
tential because they disrupt nat- 
urally occurring biological control. 
Adverse Feedback of 
Insecticide Usage 
Because of this, there is reason 
to question whether, with many 
crops and under prevailing prac- 
tice, an overall benefit results from 
insecticide use. The doubt is par- 
ticularly applicable in the case of 
cotton in California’s San Joaquin 
Valley. 
The cost of insect control in 
San Joaquin Valley probably ap- 
proaches $15 million per year. 
Much of this expense appears to 
be unnecessary. This is indicated 
from the results of a large num- 
ber of experiments in which the 
writer has been a_ participant. 
These have shown that frequently 
there is little or no gain in yield 
and/or dollar return where such 
key pests. as lygus bug and _ boll- 
worm are controled with insecti- 
cides. Extrapolation from these 
experimental results leads to the 
conclusion that, in commercial 
practice, insecticides are often ap- 
plied to pest populations which 
are either non-injurious or only 
minimally so. 
Our studies also indicate that 
much of the “pest” insect problem 
in San Joaquin Valley cotton de- 
velops. directly from insecticide 
use iteslf. That is, treatments ap- 
plied against one pest trigger out- 
breaks of others which, in turn, 
require their own chemical treat- 
ments. 
