138 



farmer and fruit-grower have gone, perhaps, to the other extreme of 

 too great faith. The case of leery a 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 Vedalia 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 for 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 exemplifications 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 



