NEW NEARCTIC SPIDER MITES OF THE FAMILY 

 TETRANYCHIDAE. 



By H. E. Ewing, 



Of the Bureau of Entomology , United States Department of Agriculture. 



Interest in the taxonomy of the spider mites (Tetranychidae) in 

 the United States has been increased during the last few years for 

 several reasons: First, because of the realization of their great 

 economic importance; second, because of the danger of introducing 

 many of the most injurious exotic species; and, third, because of the 

 difficulty found in determining correctly the most common of our 

 species. Following the earlier work of Banks and the later work of 

 the present writer, McGregor undertook a systematic review of the 

 American species, and examined more critically than had been done 

 before those characters which alone are of real specific value. As a 

 result of his investigations several mooted questions in regard to 

 synonymy have been cleared up. Yet the task of revision has in 

 no way been completed, for one is constantly finding new characters 

 and new differences which change previous judgments in regard to 

 many points. New species also exist within our borders, and foreign 

 ones are constantly being brought to our shores. Hence the present 

 writer has again taken up the difficult task of taxonomic investiga- 

 tion of the different species, and as a result of this work here offers 

 the description of eight new species. 



Genus OLIGONYCHUS Berlese. 



The genus Oligonychus Berlese (1886) is based upon a species 

 represented as having the tarsi each provided, in addition to the 

 tenent hairs, with a simple claw and a deflexed plumose, claw-like 

 structure. This type of tarsal armature must be very rare in the 

 spider mites, for recent workers have dropped the genus Oligonychus 

 because they knew of no species having the tarsal appendages of the 

 type shown by Berlese. During the last year the writer has observed 

 two species with a deflexed, plumose, claw-like appendage to each 

 trasus. These species also show other characters which allies them 

 with the type species of Oligonychus. They are here described. 



Proceedings U. S. National Museum, Vol. 59— No. 2394. 



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