June, '11] WILSON: cotton red spider 337 



NOTES ON THE RED SPIDER ATTACKING COTTON IN SOUTH 



CAROLINA 1 



By H. F. Wilson, 



Oregon Agricultural College, Formerly Entomological Assistant, Bureau of Entomology, 

 United States Department of Agriculture. 



During the spring and summer of 1910 the writer, while an assistant 

 in the United States Bureau of Entomology, worked under the direction 

 of W. D. Hunter, in charge of Southern Field Crop Insect Investi- 

 gations, at Batesburg, S. C, for the purpose of investigating red spider 

 injury to cotton. At that time Tetranychus gloveri Banks was supposed 

 to be the pest in question and a project was planned under that 

 head. Later developments proved that Tetranychus himacula'ius 

 Harvey was the real pest. The circumstances which lead to this con- 

 clusion will be given below. 



With the idea of locating the winter stages of T. gloveri a number of 

 procedures were attempted. All evergreens and perennials were 

 examined, the first to find the plants upon which the mites might 

 remain feeding over winter and the second to locate the winter stages 

 about the roots. T. himaculaius was found February 5th in all stages 

 upon the under side of leaves of a bush {Thea japonica L.) in a door- 

 yard. A little later in the spring they were found on wild blackberry 

 canes and on cultivated violets. Little attention was paid to this 

 species at that time as T. gloveri was supposed to be the pest. By 

 May first, this species not having been located and T. bimaculatus 

 being very abundant on a number of weeds as Chenopodium botrys and 

 Datura sp. as well as on cotton, plans were made to carry on life history 

 work with the second species. These notes cover a period of from May 

 ■6 to August 16. 



Mites were transferred to potted cotton plants and these were set 

 in the insectary so that other mites could not reach them. From 

 time to time these mites were examined to determine whether they 

 were T. gloveri. They were all determined as T. bimaculatus by Mr. 

 Nathan Banks of the United States Bureau of Entomology. Single 

 leaves of Chenopodium botrys were used to carry on the work as they 

 would not wilt for from twelve to fourteen days when carefully handled. 

 In cases where the leaves wilted it was found that the mites would 

 migrate to fresh leaves and so each vial holding a single leaf was placed 

 in holders which were entirely surrounded with water. 



T. bimaculatus began to appear abundantly on cotton in the fields 



' Published by permission of the Chief of the Bureau of Entomology of the United States Department 

 of Agriculture. 



