THE TAXONOMIC VALUE OF THE CHARACTERS OF THE MALE 

 GENITAL ARMATURE IN THE GENUS 

 TETRANYCHUS DUFOUR. 



By H. E. EwiXG. 

 Oregon Agricultural College, Corvallis, Or. 



INTRODUCTION. 



The red spiders of the genus Tetranychiis 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 

 Tariation 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. 



After examining hundreds of specimens from many parts of 

 the United States, with magnifications up to 2000 diameters, 

 and using an oil emersion lens, the present writer has found that 

 the genital armature of the male is excellently adapted for 

 systematic purposes. 



The genital armature of the male may be considered as being 

 composed of the penis, its attachments, and the slit-like opening 

 through which it is protruded. For our purposes the penis alone 



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