THE RED SPIDER ON COTTON. 7 



should follow that the thick broadcasting of a narrow border strip 

 along the edge of a field adjoining a source of infestation would serve 

 as a trap crop to intercept the majority of migrating spiders. This 

 strip should be plowed in as soon as there seems to be danger of a 

 general movement to the main field. (For a practical test of this 

 idea, see under l*revention, p. 10.) 



NATURE OF DAMAGE. 



Cotton seedlings 2 inches high were found infested on May 1, but 

 not until June 1 did the work of the pest become noticeable. The 



Fig. 3. — a. Cross section of norm;il cotton leaf ; b, cross section of cotton loaf injured by 

 the red spider. The puncture is near lower ri,<;lit-liand comer. Highly magnified. 

 (Original. ) 



presence of the pest on cotton is first revealed bv the appearance on 

 the upper surface of the leaf of a blood-red spot. As leaves become 

 badly infested they redden over the entire surface, become distorted, 

 and drop. The lower leaves are first attacked, but infestation spreads 

 upward until often only the bare stalk and one or two terminal 

 leaves remain. Such plants almost invariably die. The injury tt) 

 the leaf and the discoloration which follows the feeding of the mites 

 are easily understood by referring to figure o, which represents {a) 

 the appearance of health}' cotton leaf-tissues and {!>) the condition 

 of the tissue after feeding by the pest. As previously intimated, the 

 worst spots of infestation are usually to be found in close proximity 



