458 An7ials Entomological Society of America [Vol. VI, 



Male: Similar to the male of T. telarius Linn., except for the penis. 

 Penis long, straight. Inner lobe about equal to basilar lobe in length. 

 Shaft shaped like a slender rod. Basilar lobe very pronounced, cone- 

 shaped, equal to about one fourth the length of the shaft. Hook absent. 

 Barb knob-like. 



From Coast Range Moutains, Benton Co., Oregon; on 

 Spirea sp. ; by the writer. 



This form is very closely related to another species, the 

 discription of which follows. 



Tetranychus flavus n. sp. 



For over a year I have been studying a form of red spider 

 which is a serious orchard pest in Oregon. It especially is injur- 

 ious to apples when they are growing above an elevation of 

 1000 feet above sea level. In Hood River Valley I have found 

 this form so serious as to discolor the leaves of whole orchards 

 of apples, and in some instances as to cause defoliation late in 

 the summer. When fall comes and the trees drop their leaves, 

 these mites all become a pale yellow in color and collect in masses 

 about the trunks of trees and the cracks of the ground for a 

 region of several feet from the tree bases. Here they pass the 

 winter, and become active again in the spring when the trees 

 put out their foliage. At first I considered this species as but 

 a form of our common T. telarius L. After studying these two 

 forms for two seasons in the laboratory, I find that they must 

 be considered as distinct species. This species is even more 

 closely related to the one just described, T. borealis n. sp. It 

 may be described as follows: 



General appearance similar to T. borealis n. sp.; also similar to T. 

 telarius Linn., but the individuals are smaller. Color of immature forms 

 green or yellow; of adults green or yellow, with black markings not 

 pronounced. Adults are never orange or red. In the winter when 

 deprived of food supply all instars yellow. General structures similar 

 to those of T. telarius Linn., but the tarsal claw in most instances is only 

 five-cleft, the two inner prongs being united. In T. telarius Linn., the 

 tarsal claw is, I find, six-cleft; however, it has been represented by 

 others as being four- cleft. In the case of the female of T. flavus the anal 

 spines are situated farther forward than in T. telarius Linn., and also 

 nearer the margins of the genital slit or opening. This species differs 

 from T. borealis n. sp. in the tarsal characters which are nearer those of 

 T. telarius Linn., and in having no barb to the penis. 



The penis of this species is entirely different from the penis of T. 

 telarius Linn. It is long and spine-like. In length it is equal to a third 

 or fourth of the entire length of the body. Inner lobe of penis not prom- 



