Circular No. 1 72. issued May 17, 1913. 



United States Department of Agriculture, 



BUREAU OF ENTOMOLOGY. 

 L. O. HOWARD, Entomologist and Chief of Bureau. 



THE RED SPIDER ON COTTON.^ 



{Tetranychu.s hii)iacii1(ttus Harvey.) 



By E. A. McGregor, 

 Entomological Assistant. 



INTRODUCTION. 



The minute reddish mite commonly known as the red spider appar- 

 ently is becomina: one of the serious enemies of the cotton plant in 

 the United States. It is now prevalent throughout the cotton belt, 

 and, especially in the last few seasons, has caused much alarm amon<j 

 the farmers in certain sections. Seasons of excessive drought are 

 favorable to the development of the mite, and at such times the pest 

 increases so rapidly that the damage often becomes severe before its 

 presence is detected. 



Red-spider infestation is frequently miscalled "rust" by farmers, 

 since infested leaves soon turn deep red on their upper surface. Such 

 leaves, hoAvever, if examined underneath, reveal the presence of the 

 red spiders and the inconspicuous webs behind which they are feed- 

 ing and laying their eggs. 



HISTORY AND DISTRIBUTION. 



With the exception of an outbreak in Louisiana, reported by Prof. 

 H. A. Morgan in 1893, severe occurrence of the red spider on cotton 

 had not been reported until 1003. at which time complaints of dam- 

 age came from South Carolina and Georgia. In 1904 Mr. E. S. G. 



1 This circular is based primarilj' upon work done at Batesburg, S. C, in 1911 and 1912, 

 under the direelion of Mr. W. D. Hunter, but also includes the results of observations by 

 Messrs. G. A. Runner and II. F. Wilson during the two preceding seasons. It is a revision 

 of and supersedes Circular No. 150. 



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