THE LIFE HISTORY OF THE ALDER BLIGHT APHIS. 



INTRODUCTION. 



For many years past the writer has spent much time in studying 

 the insects of the famil}^ Aphidida^, or plant-lice, in the office and 

 laboratory and in the field. In jDerhaps no other group of insects is 

 a thorough knowledge of the life histories so necessary to correct 

 conceptions of the species and the differences between them. These 

 life-history studies are often rendered especially difficult from the 

 well-known fact that many of these aphides have a secondary or 

 alternate food plant. In the case of injurious species it sometimes 

 happens that the main injury is to the alternate food plant, and the 

 discovery of the primary food plant furnishes the key to the most 

 effective way of controlling the species. A notable example of this 

 is the hop aphis {Phorodon humuli Schrank) which lays its eggs 

 and passes the winter on the plum, and which is best combated by 

 destroying or spraying the wild or cultivated plum trees at the 

 seasons of the year when the aphis is present on this food plant, 

 rather than by measures directed against the insect during the 

 summer when it occurs on the hopvines. 



The writer has worked out the life histories of several of the 

 aphides which have alternate food plunts. Among these may be 

 mentioned Hormaphis hamamelidis Fitch and H aTnamelistes spino- 

 sus Shimer, which inhabit both the witch-hazel and the birch,^ the 

 hop aphis, just mentioned, and others. 



Investigations by the writer of the present species, which has 

 heretofore been confused under various names, were begim in 1878 

 and have been continued up to the year 1911. They have resulted 

 in straightening out the sjmonymy of the species and furnished con- 

 clusive proof that the Pemphigus acerifolii of Riley, described from 

 the maple, and the (Eriosonia) Pemphigus tessellata of Fitch, de- 

 scribed from the alder, are merely forms or series of one and the 

 same species, which should now be known as Prociphilus tessellata 

 (Fitch). 



1 Toch. Ser. No. 9, Div. Ent., U. S. Dept. Agr., 1901. 



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