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farmer and fruit-grower have gone, perhaps, to the other extreme of 
too great faith. The case of Icerya and Vedalia, as I have frequently 
pointed out, was exceptional and one which can not easily be repeated. 
One of the humorous phases of the Yedalia experiment is, that the 
wide newspaper circulation of the facts — not always most accurately 
set forth — has brought me communications from all parts of the world 
asking &r supplies of the renowned little Ladybird for use against 
injurious insects of every kind and description, the inquiries being 
made, of course, under a misapprehension of the facts. 
While this California experience thus affords one of the most striking 
illustrations of what may be accomplished under exceptional circum- 
stances by the second method of utilizing beneficial insects, we can 
hardly expect to succeed in accomplishing much good in this direction 
without a full knowledge of all the ascertainable facts in the case and 
a due appreciation of the profounder laws of nature, and particularly of 
the interrelations of organisms. Year in and year out, with the condi- 
tions of life unchanged by man's actions, the relations between the 
plant-feeder and the predaceous and parasitic species of its own class 
remain substantially the same, whatever the fluctuations between them 
for any given year. This is a necessary result in the economy of 
nature ; for the ascendancy of one or the other of the opposing forces 
involves a corresponding fluctuation on the decreasing side, and there 
is a necessary relation between the plant-feeder and its enemies, which, 
normally, must be to the slight advantage of the former and only 
exceptionally to the great advantage of the latter. 
This law is recognized by all close students of nature, and has often 
been illustrated and insisted upon by entomologists in particular, as 
the most graphic exenrplifications of it occur in insect life, in which 
fecundity is such that the balance is regained with marvelous rapidity, 
even after approximate annihilation of any particular species. But it 
is doubtful whether another equally logical deduction from the prev- 
alence of this law has been sufficiently recognized by us, and this is, 
that our artificial insecticide methods have little or no effect upon the 
multiplication of an injurious species, except for the particular occa- 
sion which calls them forth, and that occasions often arise when it were 
wiser to refrain from the use of such insectides and to leave the field 
to the parasitic and predaceous forms. 
It is generally when a particular injurious insect has reached the 
zenith of its increase and has accomplished its greatest harm that the 
farmer is led to bestir himself to suppress it, and yet it is equally true 
that it is just at this time that nature is about to relieve him in strik- 
ing the balance by checks which are violent and effective in proportion 
to the exceptional increase of and consequent exceptional injury done 
by the injurious species. Now the insecticide method of routing this 
last, under such circumstances, too often involves, also, the destruc- 
tion of the parasitic and predaceous species, and does more harm than 
