154 MASS. EXPERIMENT STATION BULLETIN 179. 



could be given, and in many cases the injury by these mites resulted in 

 serious losses. Thus it soon became evident that some line of investiga- 

 tion should be conducted on the control of this mite attacking greenhouse 

 crops, and in October, 1915, this problem was assigned to me. 



The investigations upon which this paper is based were carried on under 

 the direct supervision of Dr. H. T. Fernald. The thanks of the ^vTiter 

 are due Dr. H. T. Fernald, Dr. G. C. Crampton and Dr. W. S. Regan for 

 their interest throughout the progress of the work. Acknowledgments 

 are also due the chemistrj^ department of the station for its co-operation, 

 expecially to Dr. E. B. Holland for his interest and careful manufacture of 

 man}^ complicated spray materials which led to the discovery of an efficient 

 control for the greenhouse red spider. The writer is also under obligations 

 to Mr. H. F. Tompson, professor of market gardening, for suggesting 

 this research and for much valuable information concerning the efficiency 

 of control measures when used in commercial houses. To Mr. M. E. 

 Moore of Arlington and Mr. J. Winthrop Stone of WatertoAvn the writer 

 gratefully acknowledges his indebtedness for their kind co-operation in 

 allowing promising materials to be thoroughly tested on a commercial 

 scale in their greenhouses. 



As this paper has to deal primarily with the control of the greenhouse 

 red spider, other more biological phases will be discussed only briefly, 

 unless they have a direct bearing upon control measures. 



HISTORY AND DISTRIBUTION. 



The greenhouse red spider of New England was first described by 

 Harvey in 1893 as Tetranychus bimaculatus. He considered it distinct 

 from the European species Tetranychus telarius Linn., and later workers 

 have failed to prove conclusively the identity of these species. 



The first account of serious injury caused by this mite in the United 

 States came from the New England States, where it caused much damage 

 to greenhouse plants. In 1855 a mite, since described by Banks as T. 

 gloveri, but now known as T. bimaculatus Harvey, was reported bv Glover 

 as doing injury to the cotton plants of the south. This injury increased 

 in importance, and in 1900 the Bureau of Entomology, United States 

 Department of Agriculture, established a southern laboratory to work on 

 the control of this pest. With the development of greenhouses in the 

 west the ravages of the red spider soon appeared and caused serious 

 damage to greenhouse plants as well as to many cultivated garden plants 

 and fruit trees. A closely related mite has long been a serious pest of 

 hop plants in Europe; therefore it is not surprising that our species of 

 red spider assumes a great importance in seriously damaging hop fields 

 both in the east and far west. 



The red spider, therefore, is very generally distributed throughout the 

 United States, extending from Maine to Florida and westward to Texas 

 and California, only a few States in the western arid region being exempt 

 from the ravages of this pest. 



