430 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 3 



of the northwestern occidentalis (surely not, if occidentalis is really to 

 be united with vitis), then a distinct species. I use a varietal name 

 here, as I have in many other cases, to indicate a form the taxonomic 

 position of which is uncertain. 



LIFE HISTORY NOTES AND CONTROL OF THE COMMON 



ORCHARD MITES TETRANYCHUS BIMAC- 



ULATUS AND BRYOBIA PRATENSIS 



By G. P. Weldon, Grand Junction, Colorado 



Little is known about the wintering habits of the various species 

 of mites belonging to the genus Tetranychus. It may be of interest 

 to some of the readers of the Journal of Economic Entomology, if in 

 this article a brief account is given of the hibernation of one of the 

 more common species found in Colorado. 



During the summer seasons of 1908, 1909 and 1910, T. bimaculatus 

 has been of general occurrence throughout the orchard sections of the 

 Western Slope of Colorado, and in many cases their numbers have 

 become so abundant and their attacks so severe, that considerable 

 injury to trees and fruit has been the result. 



Hibernation of T. bimaculatus. — In the spring of 1908 a number 

 of apple trees were banded with " tree tanglefoot " to trap the woolly 

 aphis as it migrated from the roots to the branches of the trees. On 

 April 27, quite a number of the above species of mite were found in 

 the lower margin of a band, which indicated that they had hibernated 

 in the soil close to the tree. During the early fall of the same year, 

 Mr. 0. B. Whipple, who was at that time Field Horticulturist of the 

 Colorado Experiment Station, at Grand Junction, sent me some red 

 mites of this species for identification, which he had collected on the 

 ground where they had migrated in abundance from some peach trees, 

 upon the foliage of which they had been feeding. During the summer 

 of 1909, T. bimaculatus was very plentiful on orchard trees at Pali- 

 sade, Colo., and I had an opportunity of observing the same thing. 

 On August 9, the mites were found to be leaving the trees in great 

 numbers. There were so many of them that the ground was literally 

 red in places, and their silvery webs were everywhere to be seen. An 

 examination of clods of earth in the orchard, showed that the mites 

 had sought shelter beneath them, and they were found going into the 

 soil at distances up to fully eight feet from the nearest tree. Upon 

 breaking open small clods hundreds of the mites would often be found 

 within. Webs were found in the little soil spaces, and a careful search 



