Ewing, H.E., 1913.
The taxonomic value of characters of the male genital armature in the genus Tetranychus Dufour.. Annals of the Entomological Society of America, 61 (4): 453-460.
Abstract
The red spiders of the genus Tetranychus Dufour have always offered a knotty problem for systematists working in the order Acarina. When these mites were first noticed they were found on such a multitude of host plants, and showed such a great variation in color that the early workers considered the genus as being made up of a great many species or varieties. Later it was found that certain well known forms could have a great variety of hosts, also that there was a considerable variation in size and color among individuals on a single host plant. Then there was a tendency to lump the forms together into a very few species, although confusion as to synonymy still remained. In 1877 Professor A. T. Tozzetti called attention to the systematic value of the characters of the mouth-parts and of the tarsal appendages. Later Professor A. Berlese made use of some very important characters, the variations of the specialized setae on the palpal thumb. In 1900 Mr. N. Banks in his, “Red spiders of the United States,” showed that the characters used by both of these authors were of special value in helping to separate our American forms. It is to Mr. Banks that we should give the credit for first straightening out many of the synonymous and wrongly determined species found in our country. But as yet, both in this country and in Europe, there is much confusion in regard to the identity and synonymy of some of our best known and most injurious species.
