370 BIOLOGICAL CONTROL 



I. Parasite^ Introductions 



Biological control has been notably successful in certain cases 

 where injurious insects have become established in lands they did 

 not previously inhabit, and have there developed into persistent 

 pests. In such instances the noxious species have been free from 

 the attacks of the parasites which restrain them in their country 

 of origin. Biological control aims at restoring the condition of 

 natural equilibrium by the introduction of the missing parasite 

 factor. The first definite experiment of this character appears to 

 have been made in 1873, when Planchon and Riley introduced 

 an American predatory mite (Tyroglyphus phylloccerce Riley) into 

 France for the purpose of endeavouring to secure a measure of 

 natural control over the Phylloxera of the vine. Although the 

 mite became established, no appreciable restraint over the pest 

 resulted, and control to-day has to be exercised by other methods. 

 In 1883 Riley attempted the control of the cabbage white butterfly 

 (Pieris rupee L.) by importing into North America one of its chief 

 European enemies, the Braconid Apanteles glomeratus. This 

 parasite has become well established. 



The Introduction of Vedalia into California. Biological control 

 received its first stimulus in the subjugation of the fluted or 

 cottony-cushion scale (leery a purehasi) in California. In the 

 year 1886 the leery a became so virulent a pest in the orange and 

 lemon groves of that state that the matter attracted national 

 attention. Accidentally introduced on plants imported from 

 Australia, it multiplied to a degree which threatened the industry 

 concerned with extinction. The mission of A. Koebele, on behalf 

 of the U.S. Dept. of Agriculture, to study the natural enemies of 

 the fluted scale in its original habitat has often been recounted. 

 Suffice to say, he discovered in the small Coccinellid beetle, 

 Vedalia ^ cardinalis, an extraordinarily efficient predator. Its 

 successful transmission from Sydney to Los Angeles was speedily 

 followed by its liberation in the open, and in less than five years 

 the Icerya was so completely destroyed that the survivors became 



^ As a convenience, the word " parasite " is often used in this chapter in a 

 general sense which implies both parasites and predators. 

 - Now known as Rodolia cardinalis. 



