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The red spiders of America and a few European species likely to be introduced

E. A. McGregor
1920 Proceedings of the United States National Museum  
The so-called red spiders or s{)innmomites (which were all included in the genus Tetranychus until within the last few years) are without doubt the most important economically of the mites, and cause gi-eat damage annually to many of the most valuable cultivated plants. The writer has previously estimated that at normal prices the cotton crop of the United States may suffer through the ravages of the common red spider (Tetranychus himacvlatus Harvey) to the extent of $2,000,000. Leading crops
more » ... 00. Leading crops in various parts of the world are Imown to suffer similarly. As Tragardh and others have pohited out, the systematic knowledge of the red spiders is by no means on a plane with the comprehension of their economic status. Moreovei-, not until the completion, recently, of the investigation of the red spider on cotton (23 )2 by the Bureau of Entomology, was much known as to accurate details of their biology. Banlcs in the United States and Berlese in Europe were the pioneers who undertook the taxonomic separation of the species of this group. As Zacher (13) and the present writer (20) have already pointed out, the ordinary microscopic equipment with which these mites previously have been studied was far too crude, and only on such grounds could the finer taxonomic details have escaped such excellent observers as the two above mentioned pioneer acaridologists. In Banks's Red Spiders of the United States (9) he separates the species chiefly through the palpal and tarsal characters. These are still very useful in the taxonomy of the group, but to them have been added the so-called collar tracheae and the penis. In order properly to examine these structures it is absolutely necessary to employ an ' Since this paper was written the author has resigned from the Bureau of Entomology. " The numbers in parentheses refer to " References " at the end of this paper.
doi:10.5479/si.00963801.56-2303.641 fatcat:kcdz4tvgsjhibjp7wcaivznp2u