SB 

 818 

 C578 

 ENT 



No. 65. 



Jnited States Department of Agriculture, 



BUREAU OF ENTOMOLOGY. 

 L. O. HOWARD, Entomologist. 



THE COTTON RED SPIDER. 



(Tetranychus gloveri Bks.) 

 By E. S. G. Titus, Special Field Agent. 



Injury to cotton by the red spider, or rust-mite as it is also called, 

 has been quite prevalent in some sections of the cotton-growing area of 

 tins country during the past two years. The cause of the injury is a 

 minute yellowish-red mite which feeds on the cotton plant, principally 

 on the under sides of the leaves, but at times attacking all parts of the 

 plant. The mites usually appear early 

 in the season, but do little appreciable 

 damage until midsummer or later. The 

 injuries rarely become serious unless 

 accompanied by long-continued dry 

 weather; in such an event the multipli- 

 cation of the mites is very rapid, and the 

 consequent injuries are often sufficient 

 to kill the plants. 



The early attacks of this mite are quite 

 characteristic; the leaves presenting on 

 the upper side near the base a scarlet 

 appearance, which, occurring at first be- 

 tween the larger ribs, gradually spreads 

 over the leaf as the mites multiply, then 

 dies out and is replaced by a dirty yellow, 

 the leaf finally shriveling and falling to 

 the ground. Larger and older leaves 

 show the effect of the attack before 

 younger leaves. 



The mites feed on the under side of the leaves, protected by a loose, 

 irregular web stretching at first from vein to vein, but later attached at 

 any point and in cases of severe injury sometimes covering both sides 

 of the leaf. 



Rarely have the red spiders been found feeding on the upper side of 

 the leaves, and then only when they are protected or shaded by the 

 leaves above, or when a leaf has begun to curl from their injuries. 



When present in considerable numbers almost all parts of the plant 



may be attacked — flowers, squares, bolls, and stems. Severely injured 



plants lo^e most of their leaves, flowers, and younger forms; quite often 



only the young unfolding leaves at the tips of the branches are left green. 



32376— No. 65—06 



Fig. 



1. — Tetranychus gloveri: Adult- 

 much enlarged (original). 



