WHOLE VOL. APTLIED ENTOMOLOGY HOWARD S^S 



forms of the woolly root-louse of the apple, has heen taken from the 

 United States to France and distributed, either from the United 

 States or from France, to England, Switzerland, Germany, Italy, New 

 Zealand, Australia, South Africa, Uruguay, Argentina, and Chile, 

 with somewhat varying results l)Ut on the whole admirable ones. In 

 New Zealand and Australia especially, this species has spread rapidly 

 and has controlled the injurious forms. 



And there are many other instances. A great mass of work has 

 been done. Very many species have been tried out. Many importa- 

 tions have been unsuccessful. Some of these have been unsuccessful 

 because of faulty methods of one kind or another. Others again have 

 been successful in spite of what we are coming to know are faulty 

 methods. The whole subject of insect parasitism is being studied by 

 a rapidly increasing number of well trained men. The early work of 

 Fiske in his especial studies of the parasitism of the gipsy moth and 

 the brown-tail moth, as displayed in Bulletin No. 91, new series, of 

 the Bureau of Entomology, have been followed by the close and philo- 

 sophical study of the phenomena of insect parasitism especially as 

 relates to the parasites of the European corn borer by W. R. Thomp- 

 son ; and some of the men in Hawaii, notably Pemberton and Willard, 

 have developed points of much practical importance. We are finding 

 that the question is one which is infinitely more complicated than we 

 had supposed 20 years ago, and that the early views of the Cali- 

 fornians, based upon a single and very exceptional instance, were in 

 fact nothing less than absurd. Especial studies must be made in every 

 individual case, and these studies must be made by highly trained ex- 

 perts. There are always many dangers to be studied and avoided ; and, 

 while certain general principles hold, there are many facts connected 

 with each individual species which must be understood. I do not 

 waver in my unfailing belief in the basic value of the principle of 

 biological control, but my outlook becomes more or less confused when 

 I consider the complications. There can be no doubt, however, that 

 the subject deserves the most careful study in every case, and there 

 can be no doubt that many times great practical results may be reached 

 by the importation of the parasites of accidentally imported injurious 

 forms. 



In 1925 an important paper was published in Paris with the title 

 " LTmportation Pour les Besoins de I'Agriculture d'lnsects Entomo- 

 phages Strangers." It was written by Dr. B. Trouvelot, of the Station 

 entomologique de Paris, and was published in the Revue de Zoologie 

 agricole et appliquee, Nos. 6 and 7, 1925. In this paper the author 

 has listed chronologically international efforts in parasite introduction, 



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